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Genotypic and phenotypic spectrum of infantile liver failure due to pathogenic TRMU variants

Open AccessPublished:October 28, 2022DOI:https://doi.org/10.1016/j.gim.2022.09.015

      ABSTRACT

      Purpose

      The study aimed to define the genotypic and phenotypic spectrum of reversible acute liver failure (ALF) of infancy resulting from biallelic pathogenic TRMU variants and to determine the role of cysteine supplementation in its treatment.

      Methods

      Individuals with biallelic (likely) pathogenic variants in TRMU were studied through an international retrospective collection of de-identified patient data.

      Results

      In 62 individuals, including 30 previously unreported cases, we described 48 (likely) pathogenic TRMU variants, of which, 18 were novel. Of these 62 individuals, 42 were alive at a median age of 6.8 (0.6-22) years after a median follow up of 3.6 (0.1-22) years. The most frequent finding, occurring in all but 2 individuals, was liver involvement. ALF occurred only in the first year of life and was reported in 43 of 62 individuals, 11 of whom received liver transplantation. Loss-of-function TRMU variants were associated with poor survival. Supplementation with at least 1 cysteine source, typically N-acetylcysteine, improved survival significantly. Neurodevelopmental delay was observed in 11 individuals and persisted in 4 of the survivors, but we were unable to determine whether this was a primary or a secondary consequence of TRMU deficiency.

      Conclusion

      In most patients, TRMU-associated ALF is a transient, reversible disease and cysteine supplementation improved survival.

      Keywords

      Introduction

      The sudden onset of liver failure in an individual with no previous history of chronic hepatic dysfunction is termed acute liver failure (ALF). Knowledge of the underlying cause is key for decision-making about appropriate treatment, especially with regards to liver transplantation (LTX). Infections and inherited metabolic disorders are common causes of ALF and are typically confirmed using conventional diagnostic strategies for viral agents or metabolite screening. Increasingly, next-generation sequencing techniques have become the first-line diagnostic screening test and bridge the diagnostic gap in more than 30% of the cases that remain unsolved after the application of conventional diagnostics.
      • Narkewicz M.R.
      • Horslen S.
      • Hardison R.M.
      • et al.
      A learning collaborative approach increases specificity of diagnosis of acute liver failure in pediatric patients.
      TRMU is a nuclear gene encoding a crucial protein for mitochondrial translation, transfer RNA (tRNA) 5-methylaminomethyl-2-thiouridylate methyltransferase (TRMU), which catalyzes the important post-translation modification (thiolation) of mitochondrial tRNAs. Biallelic variants in TRMU underlie TRMU deficiency and were first described in association with infantile ALF.
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      In that original patient cohort of 13 individuals, 4 died of ALF, but the other 9 patients survived and showed no further hepatological or neurologic issues over the next 14 years of follow up. A further 23 cases have since been reported in the literature,
      • Schara U.
      • von Kleist-Retzow J.C.
      • Lainka E.
      • et al.
      Acute liver failure with subsequent cirrhosis as the primary manifestation of TRMU mutations.
      • Uusimaa J.
      • Jungbluth H.
      • Fratter C.
      • et al.
      Reversible infantile respiratory chain deficiency is a unique, genetically heterogenous mitochondrial disease.
      • Gaignard P.
      • Gonzales E.
      • Ackermann O.
      • et al.
      Mitochondrial infantile liver disease due to TRMU gene mutations: three new cases.
      • Taylor R.W.
      • Pyle A.
      • Griffin H.
      • et al.
      Use of whole-exome sequencing to determine the genetic basis of multiple mitochondrial respiratory chain complex deficiencies.
      • Grover Z.
      • Lewindon P.
      • Clousten A.
      • Shaag A.
      • Elpeleg O.
      • Coman D.
      Hepatic copper accumulation: a novel feature in transient infantile liver failure due to TRMU mutations?.
      • Indolfi G.
      • Iascone M.
      • Remaschi G.
      • et al.
      A child with ichthyosis and liver failure.
      • Gil-Margolis M.
      • Mozer-Glassberg Y.
      • Tobar A.
      • Ashkenazi S.
      • Zeharia A.
      • Marom D.
      [TRMU mutations – reversible infantile liver failure or multisystem disorder?].
      • Nicastro E.
      • Di Giorgio A.
      • Marchetti D.
      • et al.
      Diagnostic yield of an algorithm for neonatal and infantile cholestasis integrating next-generation sequencing.
      • Soler-Alfonso C.
      • Pillai N.
      • Cooney E.
      • Mysore K.R.
      • Boyer S.
      • Scaglia F.
      L-cysteine supplementation prevents liver transplantation in a patient with TRMU deficiency.
      • Kerr M.
      • Hume S.
      • Omar F.
      • et al.
      MITO-FIND: A study in 390 patients to determine a diagnostic strategy for mitochondrial disease.
      • Qin Z.
      • Yang Q.
      • Yi S.
      • Huang L.
      • Shen Y.
      • Luo J.
      Whole-exome sequencing identified novel compound heterozygous variants in a Chinese neonate with liver failure and review of literature.
      • Kose M.
      • Isik E.
      • Aykut A.
      • et al.
      The utility of next-generation sequencing technologies in diagnosis of Mendelian mitochondrial diseases and reflections on clinical spectrum.
      • Murali C.N.
      • Soler-Alfonso C.
      • Loomes K.M.
      • et al.
      TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.
      • Sala-Coromina J.
      • Miguel L.D.
      • de Las Heras J.
      • et al.
      Leigh syndrome associated with TRMU gene mutations.
      with TRMU deficiency now termed as transient, infantile liver failure (OMIM 613070).
      It is hypothesized that TRMU uses cysteine as the substrate for thiolation, and cysteine might be a conditionally essential amino acid in the first months of life.
      • Sturman J.A.
      • Gaull G.
      • Raiha N.C.
      Absence of cystathionase in human fetal liver: is cystine essential?.
      Therefore, L-cysteine or N-acetylcysteine (NAC) have been supplemented in individuals with TRMU deficiency, and anecdotal case reports showed beneficial effects.
      • Soler-Alfonso C.
      • Pillai N.
      • Cooney E.
      • Mysore K.R.
      • Boyer S.
      • Scaglia F.
      L-cysteine supplementation prevents liver transplantation in a patient with TRMU deficiency.
      ,
      • Murali C.N.
      • Soler-Alfonso C.
      • Loomes K.M.
      • et al.
      TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.
      However, many individuals with TRMU deficiency are reported to require LTX.
      • Gaignard P.
      • Gonzales E.
      • Ackermann O.
      • et al.
      Mitochondrial infantile liver disease due to TRMU gene mutations: three new cases.
      ,
      • Murali C.N.
      • Soler-Alfonso C.
      • Loomes K.M.
      • et al.
      TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.
      TRMU deficiency is a disorder of the mitochondrial transcript processing and mitochondrial transfer RNA modification category (international classification of inherited metabolic disorder
      • Ferreira C.R.
      • Rahman S.
      • Keller M.
      • Zschocke J.
      ICIMD Advisory Group
      An international classification of inherited metabolic disorders (ICIMD).
      ). Consequently, the synthesis of mitochondrial DNA encoded proteins is impaired and mitochondrial respiratory chain function is severely compromised, resulting in disease. Many mitochondrial diseases are characterized by multiorgan involvement, including severe and progressive neurologic deterioration.
      Hence, at least 4 important questions arise when a diagnosis of TRMU deficiency is made in an infant. What is the further course of disease? Is other organ involvement, especially neurologic involvement, to be expected? Will LTX be needed, and when should it be performed? Is supplementation with a cysteine source beneficial, and how long should this be continued?
      In this article, we present a multicenter study of 62 patients with biallelic TRMU variants identified via international collaboration and literature review and seek to answer these questions in an evidence-based manner.

      Materials and Methods

      Study design and data acquisition

      Individuals were included based on an international retrospective collection of de-identified data. Inclusion criteria were rare biallelic variants in TRMU classified as likely pathogenic or pathogenic according to the American College of Medical Genetics and Genomics/Association for Molecular Pathology guidelines.
      • Richards S.
      • Aziz N.
      • Bale S.
      • et al.
      Standards and guidelines for the interpretation of sequence variants: a joint consensus recommendation of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology.
      Eligible individuals were identified via literature review (eg, PubMed using the search term “TRMU”) and international collaborations. If individuals had been published previously, the respective authors were contacted for an update; if that was not received, only published data were included. All data were retrieved via standardized proformas agreed by participating centers.
      For phenotyping, the following variables were analyzed within this study: individual’s genetic ancestry, sex, age at last assessment, and clinical status. In addition, detailed data on liver disease, laboratory values, and clinical features of the main organ systems involved were scrutinized and recorded according to Human Phenotype Ontology terminology.
      • Köhler S.
      • Gargano M.
      • Matentzoglu N.
      • et al.
      The Human Phenotype Ontology in 2021.
      Regarding standards of evidence for therapeutic studies, we used the grading system from the Centre for Evidence-Based Medicine (http://www.cebm.net, ie, level 1c = all or none, which means [prolongation of] survival with therapy).

      In silico modeling of TRMU missense variant pathogenicity scores

      To assess the predicted effect of missense variants, commonly used prediction scores (mendelian clinically applicable pathogenicity v.3.5a and rare exome variant ensemble learner v.3.5a
      • Ioannidis N.M.
      • Rothstein J.H.
      • Pejaver V.
      • et al.
      REVEL: an Ensemble method for predicting the pathogenicity of rare missense variants.
      • Jagadeesh K.A.
      • Wenger A.M.
      • Berger M.J.
      • et al.
      M-CAP eliminates a majority of variants of uncertain significance in clinical exomes at high sensitivity.
      • Vaser R.
      • Adusumalli S.
      • Leng S.N.
      • Sikic M.
      • Ng P.C.
      SIFT missense predictions for genomes.
      ) were annotated for all biologically possible TRMU missense variants and mapped onto a linearized representation of the TRMU protein as previously shown.
      • Hebebrand M.
      • Hüffmeier U.
      • Trollmann R.
      • et al.
      The mutational and phenotypic spectrum of TUBA1A-associated tubulinopathy.
      ,
      • Lenz D.
      • Smith D.E.C.
      • Crushell E.
      • et al.
      Genotypic diversity and phenotypic spectrum of infantile liver failure syndrome type 1 due to variants in LARS1.
      We generated all biologically possible base substitutions in the TRMU coding sequence (transcript: NM_018006.5) and used the Mutalyzer Position Converter to match the resulting variant call format file to the GRCh37/hg19 reference genome. Scores were annotated using the Ensembl variant effect prediction tool. A generalized additive model was built using the geom_smooth function of the R ( R Core Team (2022). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. https://www.R-project.org/) ggplot 2 package to plot a smoothened line and CI.

      Statistics and software

      Kaplan-Meier estimates were calculated using R survival package. Bar and density plots were generated using the R ggplot2 package. Schematics and figures were compiled using Illustrator CS6 (Adobe).

      Results

      Study population

      A total of 62 individuals (24 female, 9 sex not available [NA]) from 56 families residing in 18 countries were included, of whom, 32 were previously published
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      • Schara U.
      • von Kleist-Retzow J.C.
      • Lainka E.
      • et al.
      Acute liver failure with subsequent cirrhosis as the primary manifestation of TRMU mutations.
      • Uusimaa J.
      • Jungbluth H.
      • Fratter C.
      • et al.
      Reversible infantile respiratory chain deficiency is a unique, genetically heterogenous mitochondrial disease.
      • Gaignard P.
      • Gonzales E.
      • Ackermann O.
      • et al.
      Mitochondrial infantile liver disease due to TRMU gene mutations: three new cases.
      • Taylor R.W.
      • Pyle A.
      • Griffin H.
      • et al.
      Use of whole-exome sequencing to determine the genetic basis of multiple mitochondrial respiratory chain complex deficiencies.
      • Grover Z.
      • Lewindon P.
      • Clousten A.
      • Shaag A.
      • Elpeleg O.
      • Coman D.
      Hepatic copper accumulation: a novel feature in transient infantile liver failure due to TRMU mutations?.
      • Indolfi G.
      • Iascone M.
      • Remaschi G.
      • et al.
      A child with ichthyosis and liver failure.
      • Gil-Margolis M.
      • Mozer-Glassberg Y.
      • Tobar A.
      • Ashkenazi S.
      • Zeharia A.
      • Marom D.
      [TRMU mutations – reversible infantile liver failure or multisystem disorder?].
      • Nicastro E.
      • Di Giorgio A.
      • Marchetti D.
      • et al.
      Diagnostic yield of an algorithm for neonatal and infantile cholestasis integrating next-generation sequencing.
      • Soler-Alfonso C.
      • Pillai N.
      • Cooney E.
      • Mysore K.R.
      • Boyer S.
      • Scaglia F.
      L-cysteine supplementation prevents liver transplantation in a patient with TRMU deficiency.
      • Kerr M.
      • Hume S.
      • Omar F.
      • et al.
      MITO-FIND: A study in 390 patients to determine a diagnostic strategy for mitochondrial disease.
      • Qin Z.
      • Yang Q.
      • Yi S.
      • Huang L.
      • Shen Y.
      • Luo J.
      Whole-exome sequencing identified novel compound heterozygous variants in a Chinese neonate with liver failure and review of literature.
      • Kose M.
      • Isik E.
      • Aykut A.
      • et al.
      The utility of next-generation sequencing technologies in diagnosis of Mendelian mitochondrial diseases and reflections on clinical spectrum.
      • Murali C.N.
      • Soler-Alfonso C.
      • Loomes K.M.
      • et al.
      TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.
      • Sala-Coromina J.
      • Miguel L.D.
      • de Las Heras J.
      • et al.
      Leigh syndrome associated with TRMU gene mutations.
      (Tables 1 and 2). For 13 individuals, solely the published data were available (L-TRMU-49 to L-TRMU-62
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      ,
      • Uusimaa J.
      • Jungbluth H.
      • Fratter C.
      • et al.
      Reversible infantile respiratory chain deficiency is a unique, genetically heterogenous mitochondrial disease.
      ,
      • Indolfi G.
      • Iascone M.
      • Remaschi G.
      • et al.
      A child with ichthyosis and liver failure.
      ,
      • Gil-Margolis M.
      • Mozer-Glassberg Y.
      • Tobar A.
      • Ashkenazi S.
      • Zeharia A.
      • Marom D.
      [TRMU mutations – reversible infantile liver failure or multisystem disorder?].
      ,
      • Qin Z.
      • Yang Q.
      • Yi S.
      • Huang L.
      • Shen Y.
      • Luo J.
      Whole-exome sequencing identified novel compound heterozygous variants in a Chinese neonate with liver failure and review of literature.
      ,
      • Sala-Coromina J.
      • Miguel L.D.
      • de Las Heras J.
      • et al.
      Leigh syndrome associated with TRMU gene mutations.
      ).
      Table 1Overview of TRMU variants of all individuals in this study
      No.IndividualNucleotide Change NM_018006Predicted Protein ChangeGenomic Position: hg19_updateLoFACMG/AMP RatingDetails of ACMG/AMP RatinggnomAD Allele FrequencyReference
      1TRMU-16c.2T>Cp.?46335766T>CYesPTHPVS1, PM2, PP50
      2L-TRMU-54, L-TRMU-55, L-TRMU-59c.2T>Ap.?46335766T>CYesPTHPVS1, PP5, PM20Zeharia et al,
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      Sala-Coromina et al
      • Sala-Coromina J.
      • Miguel L.D.
      • de Las Heras J.
      • et al.
      Leigh syndrome associated with TRMU gene mutations.
      3L-TRMU-57c.34_35dupp.Gly13ProfsTer1346335798–TCYesLPTHPVS1, PM20Qin et al
      • Qin Z.
      • Yang Q.
      • Yi S.
      • Huang L.
      • Shen Y.
      • Luo J.
      Whole-exome sequencing identified novel compound heterozygous variants in a Chinese neonate with liver failure and review of literature.
      4TRMU-15c.37_48dupp.Gly_Asp16dupchr22-46335800--CG…GA (12 bp)LPTHPM2, PM4, PP30.00003575Murali et al
      • Murali C.N.
      • Soler-Alfonso C.
      • Loomes K.M.
      • et al.
      TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.
      5TRMU-8, TRMU-38c.40G>Ap.Gly14Ser46731701G>ALPTHPS3, PM1, PP3, PP46.47E-5Zeharia et al
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      6TRMU-7c.44T>Gp.Val15Gly46731705T>GLPTHPM1, PM2, PP3, PP40
      7TRMU-30, TRMU-31c.117G>Ap.Trp39Ter46733710G>AYesPTHPP5, PVS1, PM20Soler-Alfonso et al,
      • Soler-Alfonso C.
      • Pillai N.
      • Cooney E.
      • Mysore K.R.
      • Boyer S.
      • Scaglia F.
      L-cysteine supplementation prevents liver transplantation in a patient with TRMU deficiency.
      Murali et al
      • Murali C.N.
      • Soler-Alfonso C.
      • Loomes K.M.
      • et al.
      TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.
      8L-TRMU-58c.162_163delp.Cys54Ter46337856-TGYesPTHPVS1, PM20Sala-Coromina et al
      • Sala-Coromina J.
      • Miguel L.D.
      • de Las Heras J.
      • et al.
      Leigh syndrome associated with TRMU gene mutations.
      9TRMU-19, TRMU-33, TRMU-34, TRMU-35, TRMU-36, TRMU-37, TRMU-47, TRMU-48, L-TRMU-49, L-TRMU-50, L-TRMU-51, L-TRMU-61, L-TRMU-62c.229T>Cp.Tyr77His46733822T>CLPTHPM1, PM2, PP3, PP4, PP50Zeharia et al,
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      Gil-Margolis et al
      • Gil-Margolis M.
      • Mozer-Glassberg Y.
      • Tobar A.
      • Ashkenazi S.
      • Zeharia A.
      • Marom D.
      [TRMU mutations – reversible infantile liver failure or multisystem disorder?].
      10L-TRMU-57c.244T>Gp.Phe82Val46733837T>GLPTHPM1, PM2, PM3, PP40Qin et al
      • Qin Z.
      • Yang Q.
      • Yi S.
      • Huang L.
      • Shen Y.
      • Luo J.
      Whole-exome sequencing identified novel compound heterozygous variants in a Chinese neonate with liver failure and review of literature.
      11TRMU-14c.246C>G
      Transcript annotation NM_001282782.
      p.Phe82Leu46337942C>GLPTHPM1, PM2, PP3, PP40Murali et al
      • Murali C.N.
      • Soler-Alfonso C.
      • Loomes K.M.
      • et al.
      TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.
      12TRMU-5c.248+1G>Ap.?46337945G>AYesPTHPVS1, PM20Gaignard et al
      • Gaignard P.
      • Gonzales E.
      • Ackermann O.
      • et al.
      Mitochondrial infantile liver disease due to TRMU gene mutations: three new cases.
      13TRMU-22, TRMU-23, TRMU-27, TRMU-46c.287A>Gp.Asn96Ser46739197A>GLPTHPM1, PM2, PP3, PP40Taylor et al
      • Taylor R.W.
      • Pyle A.
      • Griffin H.
      • et al.
      Use of whole-exome sequencing to determine the genetic basis of multiple mitochondrial respiratory chain complex deficiencies.
      14L-TRMU-60c.304A>Gp.Asn102Asp46343317A>GLPTHPM2, PP3, PP50Indolfi et al
      • Indolfi G.
      • Iascone M.
      • Remaschi G.
      • et al.
      A child with ichthyosis and liver failure.
      15TRMU-40c.339T>Gp.Tyr113Ter46739249T>GYesPTHPVS1, PM2, PP40
      16TRMU-42c.383A>Gp.Tyr128Cys46742346A>GLPTHPM1, PM2, PP3, PP40Nicastro et al
      • Nicastro E.
      • Di Giorgio A.
      • Marchetti D.
      • et al.
      Diagnostic yield of an algorithm for neonatal and infantile cholestasis integrating next-generation sequencing.
      17L-TRMU-59c.491delp.Leu164ProfsTer2246350303-TYesLPTHPV1, PM20Sala-Coromina et al
      • Sala-Coromina J.
      • Miguel L.D.
      • de Las Heras J.
      • et al.
      Leigh syndrome associated with TRMU gene mutations.
      18TRMU-29c.493C>Ap.Gln165Ter46746202G>AYesPTHPVS1, PM20
      19L-TRMU-53c.500_510delp.Ala167GlufsTer3646350312-CT…TT (11 bp)YesPTHPV1, PM20Zeharia et al
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      20TRMU-27c.521C>Tp.Thr174Ile46746230C>TLPTHPM1, PM2, PP3, PP40
      21TRMU-14c.525_527delp.Phe176del46350334-CTTLPTHPM2, PM4, PP3, PP50.00001193Murali et al
      • Murali C.N.
      • Soler-Alfonso C.
      • Loomes K.M.
      • et al.
      TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.
      22TRMU-24c.530T>Ap.Leu177His46746239T>ALPTHPM1, PM2, PP3, PP40
      23TRMU-44c.581delp.Gly194AspfsTer246746284-TG-TYesPTHPVS1, PM2, PP50.00002475
      24TRMU-1c.589A>Cp.Lys197Gln46746298A>CLPTHPM1, PM2, PP3, PP40Kerr et al
      • Kerr M.
      • Hume S.
      • Omar F.
      • et al.
      MITO-FIND: A study in 390 patients to determine a diagnostic strategy for mitochondrial disease.
      25TRMU-44c.611C>Tp.Ala204Val46746320C>TLPTHPM1, PM2, PP3, PP40
      26TRMU-40c.646_648delp.Lys216del46350458-AAALPTHPM2, PM4, PP30
      27TRMU-11c.649G>Ap.Glu217Lys46746358G>ALPTHPM1, PM2, PP3, PP40Gaignard et al
      • Gaignard P.
      • Gonzales E.
      • Ackermann O.
      • et al.
      Mitochondrial infantile liver disease due to TRMU gene mutations: three new cases.
      28TRMU-39, TRMU-41c.653G>Tp.Ser218Ile46748019G>TLPTHPM1, PM1, PM2, PP3, PP4, PP50
      29TRMU-10c.664T>Gp.Cys222Gly46748030T>GLPTHPM1, PM2, PP3, PP40
      30TRMU-45c.671T>Gp.Ile224Ser46748037T>CLPTHPM1, PM2, PP3, PP4, PP50
      31TRMU-30, TRMU-31, L-TRMU-58c.680G>Cp.Arg227Thr46748046G>CLPTHPM1, PM2, PP3, PP4, PP50Soler-Alfonso et al,
      • Soler-Alfonso C.
      • Pillai N.
      • Cooney E.
      • Mysore K.R.
      • Boyer S.
      • Scaglia F.
      L-cysteine supplementation prevents liver transplantation in a patient with TRMU deficiency.
      Murali et al,
      • Murali C.N.
      • Soler-Alfonso C.
      • Loomes K.M.
      • et al.
      TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.
      Sala-Coromina et al
      • Sala-Coromina J.
      • Miguel L.D.
      • de Las Heras J.
      • et al.
      Leigh syndrome associated with TRMU gene mutations.
      32TRMU-6c.697C>Tp.Leu233Phe46748063C>TLPTHPS3, PM1, PM2, PP40Zeharia et al
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      33TRMU-47, L-TRMU-49c.706-1G>Ap?46748160G>AYesPTHPVS1, PM2, PP50.000003976Zeharia et al
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      34TRMU-32c.711dupp.Gln238AlafsTer1446748166_46748167insGYesLPTHPVS1, PM20Schara et al
      • Schara U.
      • von Kleist-Retzow J.C.
      • Lainka E.
      • et al.
      Acute liver failure with subsequent cirrhosis as the primary manifestation of TRMU mutations.
      35L-TRMU-52c.815G>Ap.Gly272Asp46353809G>ALPTHPP2, PM5, PM20Zeharia et al
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      36TRMU-20c.827C>Tp.Pro276Leu46749718C>TLPTHPM1, PM2, PP3, PP40
      37TRMU-2, TRMU-3, TRMU-4, TRMU-5, TRMU-11, TRMU-17, TRMU-25, TRMU-26, TRMU-28, TRMU-42, TRMU-43, TRMU-45, L-TRMU-53, L-TRMU-56, L-TRMU-60c.835G>Ap.Val279Met46749726G>ALPTHPM1, PM2, PP3, PP4, PP50Zeharia et al,
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      Uusimaa et al,
      • Uusimaa J.
      • Jungbluth H.
      • Fratter C.
      • et al.
      Reversible infantile respiratory chain deficiency is a unique, genetically heterogenous mitochondrial disease.
      Gaignard et al,
      • Gaignard P.
      • Gonzales E.
      • Ackermann O.
      • et al.
      Mitochondrial infantile liver disease due to TRMU gene mutations: three new cases.
      Grover et al,
      • Grover Z.
      • Lewindon P.
      • Clousten A.
      • Shaag A.
      • Elpeleg O.
      • Coman D.
      Hepatic copper accumulation: a novel feature in transient infantile liver failure due to TRMU mutations?.
      Indolfi et al
      • Indolfi G.
      • Iascone M.
      • Remaschi G.
      • et al.
      A child with ichthyosis and liver failure.
      38TRMU-8c.878C>Tp.Pro293Leu46751345C>TLPTHPM1, PM2, PP3, PP40
      39TRMU-3c.936G>Ap.Trp312Ter46751403G>AYesPTHPVS1, PM20
      40TRMU-18, TRMU-28c.954dupp.Ala319ArgfsTer8746751418-T-TCYesPTHPVS1, PM2, PP50.00004395
      41TRMU-21c.1005C>Gp.His335Gln46751472C>GLPTHPM1, PM2, PP3, PP40
      42TRMU-2c.1041_1044delp.Asn347LysfsTer746356008-TCAAYesPTHPVS1, PM20Grover et al
      • Grover Z.
      • Lewindon P.
      • Clousten A.
      • Shaag A.
      • Elpeleg O.
      • Coman D.
      Hepatic copper accumulation: a novel feature in transient infantile liver failure due to TRMU mutations?.
      43TRMU-9, TRMU-24, TRMU-32, TRMU-39, TRMU-41c.1073_1081dup
      Indicates referred to in literature as: c.1066_1074dup (c.1073_1081dup), c.1073_1081dup, c.1081_1082insAGGCTGTGC.
      p.Gln358_Val360dupg.46751934_46751942dupLPTHPS30.00002477Schara et al
      • Schara U.
      • von Kleist-Retzow J.C.
      • Lainka E.
      • et al.
      Acute liver failure with subsequent cirrhosis as the primary manifestation of TRMU mutations.
      44TRMU-1c.1081C>Tp.Arg361Cys46751949C>TLPTHPM1, PM2, PP3, PP43.23E-5Kerr et al
      • Kerr M.
      • Hume S.
      • Omar F.
      • et al.
      MITO-FIND: A study in 390 patients to determine a diagnostic strategy for mitochondrial disease.
      45TRMU-12, TRMU-13c.1084G>Ap.Ala362Thr46751952G>ALPTHPM1, PM2, PP3, PP40Murali et al
      • Murali C.N.
      • Soler-Alfonso C.
      • Loomes K.M.
      • et al.
      TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.
      46L-TRMU-56c.1102-3C>Gp.?46356839C>GYesPTHPP3, PP5, PM20.000007093Uusimaa et al
      • Uusimaa J.
      • Jungbluth H.
      • Fratter C.
      • et al.
      Reversible infantile respiratory chain deficiency is a unique, genetically heterogenous mitochondrial disease.
      47TRMU-9c.1108G>Ap.Val370Met46752745G>ALPTHPM1, PM2, PP3, PP40
      48TRMU-4, TRMU-15c.1142G>Ap.Gly381Glu46752779G>ALPTHPM1, PM2, PP3, PP40Murali et al
      • Murali C.N.
      • Soler-Alfonso C.
      • Loomes K.M.
      • et al.
      TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.
      49TRMU-12, TRMU-13del 22q13.31 46,730,453-4,673,227YesMurali et al
      • Murali C.N.
      • Soler-Alfonso C.
      • Loomes K.M.
      • et al.
      TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.
      Variants presented in bold are novel.
      ACMG, American College of Medical Genetics and Genomics; AMP, Association for Molecular Pathology; bp, basepair; gnomAD, Genome Aggregation Database; LoF, loss of function; LPTH, likely pathogenic; PTH, pathogenic.
      a Transcript annotation NM_001282782.
      b Indicates referred to in literature as: c.1066_1074dup (c.1073_1081dup), c.1073_1081dup, c.1081_1082insAGGCTGTGC.
      Table 2Detailed individual characteristics of all TRMU-deficient individuals in this study
      PatientAliveCause of DeathAge of Death (mo)Age at First Symptoms (mo)Age at Diagnosis (mo)TRMU Variant 1 (NM_018006)TRMU Variant 2 (NM_018006)Age at Last Follow Up (mo)Hepatic SymptomsNumber of ALF EpisodesLTXSupplementationFailure to ThriveLactic AcidosisNeurodevelopmental DelayNeurodevelopmental Delay ResolvedMuscular HypotoniaGrowth AbnormalityOthersReference
      TRMU-01Yes7.5108c.589A>C; p.Lys197Glnc.1081C>T; p.Arg361Cys190x2NoAAxxYesx
      TRMU-02
      Loss of function variant.
      Yes413c.835G>A; p.Val279Metc.1041_1044del; p.Asn347LysfsTer7144x1NoNACGrover et al
      • Grover Z.
      • Lewindon P.
      • Clousten A.
      • Shaag A.
      • Elpeleg O.
      • Coman D.
      Hepatic copper accumulation: a novel feature in transient infantile liver failure due to TRMU mutations?.
      TRMU-03
      Loss of function variant.
      NoRC668c.835G>A; p.Val279Metc.936G>A; p.Trp312Ter6x1NoNox
      TRMU-04NoHF41.256c.835G>A; p.Val279Metc.1142G>A; p.Gly381Glu4x1NoNoxDeceased
      TRMU-05
      Loss of function variant.
      NoHF80.1pmc.835G>A; p.Val279Metc.248+1G>A, p?8x3YesNACxxGaignard et al
      • Gaignard P.
      • Gonzales E.
      • Ackermann O.
      • et al.
      Mitochondrial infantile liver disease due to TRMU gene mutations: three new cases.
      TRMU-06Yes0.148c.697C>T; p.Leu233Phec.697C>T; p.Leu233Phe157x0NoNoxxxGaignard et al
      • Gaignard P.
      • Gonzales E.
      • Ackermann O.
      • et al.
      Mitochondrial infantile liver disease due to TRMU gene mutations: three new cases.
      TRMU-07Yes24c.44T>G; p.Val15Glyc.44T>G; p.Val15Gly107x1NoNAC, SelxxxYes
      TRMU-08NoMOF734c.40G>A; p.Gly14Serc.878C>T; p.Pro293Leu7x1YesAA, NACx
      TRMU-09Yes832c.1073_1081dup; p.Gln358_Val360dupc.1108G>A; p.Val370Met96x0NoAAxx
      TRMU-10NoMOF0.10.1pmc.664T>G; p.Cys222Glyc.664T>G; p.Cys222Gly0.1x0NoNoxx
      TRMU-11Yes424c.649G>A; p.Glu217Lysc.835G>A; p.Val279Met120x0NoNoxxxGaignard et al
      • Gaignard P.
      • Gonzales E.
      • Ackermann O.
      • et al.
      Mitochondrial infantile liver disease due to TRMU gene mutations: three new cases.
      TRMU-12
      Loss of function variant.
      Yes1.526c.1084G>A; p.Ala362Thrdel 22q13.31 46,730,453-4,673,22760x0NoL-Cys, NACxxxYesxMurali et al
      • Murali C.N.
      • Soler-Alfonso C.
      • Loomes K.M.
      • et al.
      TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.
      TRMU-13
      Loss of function variant.
      Yes6Fetalc.1084G>A; p.Ala362Thrdel 22q13.31 46,730,453-4,673,22727x0NoL-Cys, NACxMurali et al
      • Murali C.N.
      • Soler-Alfonso C.
      • Loomes K.M.
      • et al.
      TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.
      TRMU-14Yes22.5c.246C>G
      Transcript annotation NM_001282782.
      ; p.Phe82Leu
      c.525_527del; p.Phe176del53x1YesNACxxxNoMurali et al
      • Murali C.N.
      • Soler-Alfonso C.
      • Loomes K.M.
      • et al.
      TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.
      TRMU-15NoHF30.52.5c.1142G>A; p.Gly381Gluc.37_48dup; p.G13_D16dup3x2NoNACxxxEncephalopathyMurali et al
      • Murali C.N.
      • Soler-Alfonso C.
      • Loomes K.M.
      • et al.
      TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.
      TRMU-16
      Loss of function variant.
      Yes1.752.5c.2T>C; p.?c.2T>C; p.?7.5x3NoL-Cys, NACxxNoEncephalopathy
      TRMU-17Yes214c.835G>A; p.Val279Metc.835G>A; p.Val279Met91x2YesNoxxYesx
      TRMU-18
      Loss of function variant.
      NoMOF21pmc.954dupC; p.Ala319ArgfsTer87c.954dup; p.Ala319ArgfsTer8720NoNoxxxDeceasedxCardiomyopathy
      TRMU-19Yes46c.229T>C; p.Tyr77Hisc.229T>C; p.Tyr77His104x0NoNACxxYesxx
      TRMU-20NoHF32pmc.827C>T; p.Pro276Leuc.827C>T; p.Pro276Leu3x2NoNoxx
      TRMU-21NoHF3.50.1pmc.1005C>G; p.His335Glnc.1005C>G; p.His335Gln3.5x2NoAAxxxDeceasedx
      TRMU-22Yes0.10.1c.287A>G; p.Asn96Serc.287A>G; p.Asn96Ser49x1NoNoxxxNox
      TRMU-23NoRC1.751pmc.287A>G; p.Asn96Serc.287A>G; p.Asn96Ser2x1NoNoxxxDeceasedxxCardiomyopathy
      TRMU-24Yes2NAc.530T>A; p.Leu177Hisc.1073_1081dup; p.Gln358_Val360dup11x2YesAA, L-Cys, NAC, Selxxx
      TRMU-25Yes30.1c.835G>A; p.Val279Metc.835G>A; p.Val279Met72x1NoNACxxAnemia, hyperechogenic kidneys
      TRMU-26Yes20.1c.835G>A; p.Val279Metc.835G>A; p.Val279Met54x1NoNACx
      TRMU-27Yes7.510c.287A>G; p.Asn96Serc.521C>T; p.Thr174Ile49x0NoNoxNox
      TRMU-28
      Loss of function variant.
      Yes25c.835G>A; p.Val279Metc.954dup; p.Ala319ArgfsTer8777x3YesNoxxxLost to follow up
      TRMU-29
      Loss of function variant.
      Yes36c.493C>A; p.Gln165Terc.493G>A; p.Gln165Ter96x1YesNo
      TRMU-30
      Loss of function variant.
      NoHF20.251c.117G>A; p.Trp39Terc.680G>C; p.Arg227Thr2x1NoNoxxxDeceasedxEncephalopathy, epileptic seizuresSoler-Alfonso et al,
      • Soler-Alfonso C.
      • Pillai N.
      • Cooney E.
      • Mysore K.R.
      • Boyer S.
      • Scaglia F.
      L-cysteine supplementation prevents liver transplantation in a patient with TRMU deficiency.
      Murali et al
      • Murali C.N.
      • Soler-Alfonso C.
      • Loomes K.M.
      • et al.
      TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.
      TRMU-31
      Loss of function variant.
      Yes2Fetalc.117G>A; p.Trp39Terc.680G>C; p.Arg227Thr45x1NoAA, L-Cys, NAC, SelxxLost to follow upxxSoler-Alfonso et al,
      • Soler-Alfonso C.
      • Pillai N.
      • Cooney E.
      • Mysore K.R.
      • Boyer S.
      • Scaglia F.
      L-cysteine supplementation prevents liver transplantation in a patient with TRMU deficiency.
      Murali et al
      • Murali C.N.
      • Soler-Alfonso C.
      • Loomes K.M.
      • et al.
      TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.
      TRMU-32Yes417c.711_712insG; p.Gln238AlafsX14c.1073_1081dup; p.Gln358_Val360dup105x1NoNoxSchara et al
      • Schara U.
      • von Kleist-Retzow J.C.
      • Lainka E.
      • et al.
      Acute liver failure with subsequent cirrhosis as the primary manifestation of TRMU mutations.
      TRMU-33Yes116c.229T>C; p.Tyr77Hisc.229T>C; p.Tyr77His157x1NoNoxxYesxxZeharia et al
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      TRMU-34Yes1.524c.229T>C; p.Tyr77Hisc.229T>C; p.Tyr77His172x1NoNoxxZeharia et al
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      TRMU-35Yes46c.229T>C; p.Tyr77Hisc.229T>C; p.Tyr77His93x1NoNACxxxYesxxLower limb edema
      TRMU-36Yes33c.229T>C; p.Tyr77Hisc.229T>C; p.Tyr77His73x0NoNoxx
      TRMU-37Yes3120c.229T>C; p.Tyr77Hisc.229T>C; p.Tyr77His270x1NoNoxCardiomyopathyZeharia et al
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      TRMU-38Yes0.160c.40G>A;p.Gly14SerNo maternal cDNA expression204x5NoNoxCardiomyopathyZeharia et al
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      TRMU-39Yes0.11c.653G>T; p.Ser218Ilec.1073_1081dup; p.Gln358_Val360dup40x1NoNoxxxYesEpileptic seizures
      TRMU-40
      Loss of function variant.
      NoSepsis30.1pmc.339T>G, p.Tyr113Terc.646_648del; p.Lys216del3x1NoNoxxxDeceased
      TRMU-41Yes2NAc.653G>T; p.Ser218Ilec.1073_1081dup; p.Gln358_Val360dup161x5YesAAxxxYesxHypothyroidism
      TRMU-42Yes27c.383A>G; p.Tyr128Cysc.835G>A; p.Val279Met45x1NoAAxxxNicastro et al
      • Nicastro E.
      • Di Giorgio A.
      • Marchetti D.
      • et al.
      Diagnostic yield of an algorithm for neonatal and infantile cholestasis integrating next-generation sequencing.
      TRMU-43Yes428c.835G>A; p.Val279Metc.835G>A; p.Val279Met66x0NoNoxxYesMicrocephalyKose et al
      • Kose M.
      • Isik E.
      • Aykut A.
      • et al.
      The utility of next-generation sequencing technologies in diagnosis of Mendelian mitochondrial diseases and reflections on clinical spectrum.
      TRMU-44
      Loss of function variant.
      Yes56c.581del; Gly194AspfsTer2c.611C>T; p.Ala204Val17x1YesNACxxx
      TRMU-45
      Loss of function variant.
      Yes24.5c.671T>G; p.Ile224Serc.835G>A; p.Val279Met36x0NoAA, L-Cys, NACxxxx
      TRMU-46NoMOF10.1pmc.287A>G; p.Asn96Serc.287A>G; p.Asn96Ser1x0NoNoxxxDeceasedxCardiomyopathy, encephalopathyTaylor et al
      • Taylor R.W.
      • Pyle A.
      • Griffin H.
      • et al.
      Use of whole-exome sequencing to determine the genetic basis of multiple mitochondrial respiratory chain complex deficiencies.
      TRMU-47
      Loss of function variant.
      Yes33c.229T>C; p.Tyr77Hisc.706-1G>A; p.?49x1YesNACxxxx
      TRMU-48Yes2.578c.229T>C; p.Tyr77Hisc.229T>C; p.Tyr77His223x1YesNACxx
      L-TRMU-49NoMOF43NAc.229T>C; p.Tyr77Hisc.706-1G>A; p.?4x1NoNoxZeharia et al
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      L-TRMU-50Yes4NAc.229T>C; p.Tyr77Hisc.229T>C; p.Tyr77His96x1NoNoxZeharia et al
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      L-TRMU-51Yes4NAc.229T>C; p.Tyr77Hisc.229T>C; p.Tyr77His168x1NoNoxZeharia et al
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      L-TRMU-52Yes6NAc.815G>A; p.Gly272Aspc.815G>A; p.Gly272Asp24NANANoNoxZeharia et al
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      L-TRMU-53
      Loss of function variant.
      NoMOF1NAc.835G>A; p.Val279Metc.500-510del; p.Ala167GlufsTer362x1NoNoxZeharia et al
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      L-TRMU-54
      Loss of function variant.
      NoMOF30.1NAc.2T>A; p.?c.2T>A; p.?3xNANoNoxZeharia et al
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      L-TRMU-55
      Loss of function variant.
      NoMOF40.1NAc.2T>A; p.?c.2T>A; p.?4x1NoNoxZeharia et al
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      L-TRMU-56
      Loss of function variant.
      Yes5NAc.835G>A; p.Val279Metc.1102-3C>G, p?48x0NoNoxxBulbar involvmentUusimaa et al
      • Uusimaa J.
      • Jungbluth H.
      • Fratter C.
      • et al.
      Reversible infantile respiratory chain deficiency is a unique, genetically heterogenous mitochondrial disease.
      L-TRMU-57
      Loss of function variant.
      NoRC0.10.1pmc.34_35dup; p.Gly13ProfsTer13c244T>G; p.Phe82Val0.1x1NoNoxxxQin et al
      • Qin Z.
      • Yang Q.
      • Yi S.
      • Huang L.
      • Shen Y.
      • Luo J.
      Whole-exome sequencing identified novel compound heterozygous variants in a Chinese neonate with liver failure and review of literature.
      L-TRMU-58
      Loss of function variant.
      NoHF633c.162_163del; p.Cys54Terc.680G>C; p.Arg227Thr6x1NoNoxxxDeceasedxEncephalopathySala-Coromina et al
      • Sala-Coromina J.
      • Miguel L.D.
      • de Las Heras J.
      • et al.
      Leigh syndrome associated with TRMU gene mutations.
      L-TRMU-59
      Loss of function variant.
      NoHF10.11c.2T>A; p.?c.491del; p.Leu164ProfsTer221x1NoNoxxxDeceasedxEncephalopathySala-Coromina et al
      • Sala-Coromina J.
      • Miguel L.D.
      • de Las Heras J.
      • et al.
      Leigh syndrome associated with TRMU gene mutations.
      L-TRMU-60Yes39c.304A>c; p.Asn102Aspc.835G>A; p.Val279Met60x1NoNoxxxYesxIchtyosisIndolfi et al
      • Indolfi G.
      • Iascone M.
      • Remaschi G.
      • et al.
      A child with ichthyosis and liver failure.
      L-TRMU-61Yes4NAc.229T>C; p.Tyr77Hisc.229T>C; p.Tyr77HisNAx1NoNoxAnemia, hypothyroidism, microcephalyGil-Margolis et al
      • Gil-Margolis M.
      • Mozer-Glassberg Y.
      • Tobar A.
      • Ashkenazi S.
      • Zeharia A.
      • Marom D.
      [TRMU mutations – reversible infantile liver failure or multisystem disorder?].
      L-TRMU-62Yes5NAc.229T>C; p.Tyr77Hisc.229T>C; p.Tyr77HisNAx1NoNoxAnemia, hypothyroidism, microcephalyGil-Margolis et al
      • Gil-Margolis M.
      • Mozer-Glassberg Y.
      • Tobar A.
      • Ashkenazi S.
      • Zeharia A.
      • Marom D.
      [TRMU mutations – reversible infantile liver failure or multisystem disorder?].
      Unpublished individuals are presented in bold. L-TRMU nomenclature reflects cases with only published data available. X marks the presence of a phenotypic feature.
      AA, ascorbic acid; ALF, acute liver failure; cDNA, complementary DNA; HF, hepatic failure; L-cys, L-cysteine; LTX, liver transplantation; MOF, multiorgan failure; NA, not available; NAC, N-acetylcysteine; pm, post mortem; RC, respiratory and circulatory failure; Sel, selenium.
      a Loss of function variant.
      b Transcript annotation NM_001282782.
      Of note, we did not include 1 previously published individual with compound heterozygosity for variants c.697C>T, p.(Leu233Phe) and c.28G>T, p.(Ala10Ser) (benign, found 1230 times in homozygous state in Genome Aggregation Database).
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      Data pertaining to respiratory chain enzyme activities, serum amino acid levels, organic acid profiles, and further laboratory findings are documented in Supplemental Table 1.

      Genetics

      A total of 48 different variants were identified, of these, 18 have not been reported previously (Table 1, Figure 1A). In 2 siblings (TRMU-12 and TRMU-13), a deletion encompassing more than 1 exon in phase with a recognized missense TRMU variant was detected.
      Figure thumbnail gr1
      Figure 1Genetics and clinical findings. A. All TRMU variants reported in this study are indicated by black lines above the corresponding amino acid position. TRMU protein domains and regions of important protein function are highlighted. B. Density plot of the frequency of TRMU variants reported in this study with respect to the affected protein domains. C. In silico pathogenicity prediction of all potential TRMU missense variants using REVEL score. D. LoF variants (red) influence survival probability of individuals with TRMU deficiency as compared with Kaplan-Meier estimate. E. Most prevalent clinical symptoms of the study cohort using Human Phenotype Ontology terminology. These include the following presentations: liver failure, cholestasis, and jaundice (abnormality of the liver); lactic acidosis; failure to thrive (abnormality of body weight), vomiting and diarrhea (abdominal symptom); motor delay, neurodevelopmental delay, and encephalopathy (abnormality of the nervous system); hypotonia (muscular hypotonia); and growth retardation (growth abnormality). ATP, adenosine triphosphate; LoF, loss of function; REVEL, rare exome variant ensemble learner; tRNA, transfer RNA.
      Variants were distributed throughout the gene (Figure 1A), with a higher density in the catalytic domain near the site of interaction with the target base in tRNA and in the β-barrel (Figure 1B). The most frequent variants were the missense variants c.835A>G, p.(Val279Met) and c.229T>C, p.(Tyr77His), which were detected in 15 and 13 individuals, respectively. As expected, variants showed comparable rare exome variant ensemble learner scores throughout the gene with fewer variants in the C-terminal region of the protein (Figure 1C). The 18 loss-of-function (LoF) variants and the intragenic deletion predicted to lead to loss of protein were detected at least in monoallelic state in 24 individuals. Presence of a LoF variant strongly affected on overall individual survival (P = .016) (Figure 1D). Overall survival did not differ between individuals having a LoF variant in 1 allele only and those having it in both alleles. (P = .6) (Supplemental Figure 1A).

      Phenotypic spectrum

      The cohort comprised 62 individuals, of whom, 42 were alive at the time of data collection (median age 6.8 years, range: 0.6-22.5 years, interquartile range [IQR] = 8.2 years). The median age of death was 3 (range: 0.1-8, IQR = 2) months. First symptoms were recognized at a median age of 2 (IQR = 3) months, and the genetic diagnosis was made at a median age of 6 months (IQR = 13.8). In 2 individuals, the diagnosis was made prenatally, both alive at inclusion, and in 9 individuals post mortem. The total duration of follow up of the cohort was 302 years, individually ranging from 0.1 to 22 (median = 3.6, IQR = 2.18) years.
      The most frequent finding in all but 2 individuals (60/62, 1 NA) was liver involvement (HP:0001392). Lactic acidosis (HP:0003128, 45/62), abnormal body weight (HP:004323, 39/62, 8 NA), emesis and/or diarrhea (HP:0011458, 29/62, 8 NA), abnormality of the nervous system (HP:0000707, 26/62, 5 NA), muscular hypotonia (HP:0001252, 22/62, 5 NA), and abnormal growth (HP:0001507, 21/62, 7 NA) were further commonly reported symptoms (Figure 1E). Cause of death was most frequently reported to be multiple organ failure (8/20) or hepatic failure (8/20) (Figure 2B).
      Figure thumbnail gr2
      Figure 2Individual survival and hepatic phenotype. A. Supplementation therapy (red) influences survival probability of individuals with TRMU deficiency as compared with Kaplan-Meier estimates. B. Cause of death for the 14 deceased individuals with TRMU deficiency. C. Most common features of the hepatic presentation of individuals with TRMU deficiency. D. Density plot indicating the occurrence of ALF episodes over the first 15 months of life. E. Frequency of ALF episodes per individual across the cohort. F. Survival probability of individuals with TRMU deficiency with LTX therapy (red) and without LTX therapy (blue) is compared using Kaplan-Meier estimator. ALF, acute liver failure; LTX, liver transplantation.
      The detailed metabolic findings in blood and urine, as well as respiratory-chain enzyme activities analyzed in available tissues, did not show a specific pattern and can be found in Supplemental Table 1.
      Oral supplementation of a cysteine source was reported in 40% of individuals (25/62), with NAC being most frequently used (19/25) at a median dosage of 150 (IQR = 62.5) mg/kg/d. The overall individual survival was significantly better (P = .0052) in individuals using any kind of cysteine supplementation than in the ones without cysteine supplementation (Figure 2A). This was even more significant (P = .0033) for the subgroup of 22 individuals with LoF variants (Supplemental Figure 1B).

      Abnormalities of the liver (HP:0001392)

      The most common hepatic feature reported was elevated hepatic transaminases (HP:0002910, 52/62, 5 NA). ALF (ORPHA: 90062), defined according to a recent consensus definition (ie, acute onset of liver disease without evidence of chronic liver disease and biochemical evidence of severe liver injury: prothrombin time of ≥15 seconds or international normalized ratio of ≥1.5 with evidence of hepatic encephalopathy or prothrombin time of ≥20 seconds or international normalized ratio of ≥2 with or without encephalopathy
      • Squires J.E.
      • Alonso E.M.
      • Ibrahim S.H.
      • et al.
      North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition position paper on the diagnosis and management of pediatric acute liver failure.
      ), was reported in 43 of 62 (2 NA) individuals.
      Further hepatic involvement included jaundice (HP:0000952, 34/62, 8 NA) and hepatomegaly (HP:0002240, 14/62, 4 NA) (Figure 2C). ALF episodes were reported earliest at age 2 weeks, peaking between age 1 and 5 months but were not reported after the first year of life (Figure 2D). Of 43 individuals with episodes of ALF, 33 had a single episode; although, recurrence of up to 5 episodes was reported (Figure 2E). Hepatic encephalopathy was reported in 13 individuals.
      A total of 11 individuals received LTX, which was performed during the first episode of ALF in 4 individuals and on recurrent episodes in 6 individuals. Of note, 1 individual, who received LTX because of hepatoblastoma at age 11 years was excluded from this analysis. Median age at LTX was 4 (IQR = 1.75, range 3-10) months. There was no difference in overall individual survival based on LTX (P = .079) (Figure 2F). Two individuals died despite LTX: one during surgery due to variceal bleeding and the other one shortly after LTX due to multiple organ failure. Despite its benefit on overall individual survival, supplementation therapy (eg, NAC) did not avert LTX (native liver survival, P = .24) (Figure 3A). Analysis of hepatic biopsies, performed in 31 individuals, revealed fibrotic/cirrhotic changes of hepatic parenchyma as the most frequent finding (62%), followed by macrovesicular steatosis (41%), cholestatic changes (41%), and microvesicular steatosis (43%) (Figure 3B).
      Figure thumbnail gr3
      Figure 3Native liver survival, liver histology, clinical presentation, and course of TRMU-related symptoms. A. Supplementation therapy (blue) does not influence native liver survival, ie, the need for liver transplantation, as compared with Kaplan-Meier estimates. B. Most prevalent findings in liver histopathology. C. Common clinical presentation of individuals with TRMU deficiency besides hepatic symptoms. D. Course of individuals with neurodevelopmental delay over time. Note, that 1 individual was lost to follow up. E. Less common clinical findings in individuals with TRMU deficiency.

      Nonhepatic phenotypic spectrum including neurodevelopmental outcome

      Further commonly reported symptoms of individuals with TRMU deficiency were failure to thrive (HP:0001399, 39/62, 8 NA), neurodevelopmental delay (HP:0000707, 26/62, 9 NA), muscular hypotonia (HP:0001252, 22/62, 5 NA), growth retardation (HP:0001510, 21/62, 7 NA), and motor delay (HP:0001270, 5/62, 4 NA) (Figure 3C). Neurodevelopmental delay resolved in 11 of 26 and persisted in 4 of 26 individuals to varying extents (3/4 severe, 1/4 only motor delay persisted). Another 9 of 26 individuals were reported deceased and 2 lost to follow up (Figure 3D). In the study cohort, individuals were also reported of developing encephalopathy (HP:000129, 6/62, 4 NA), cardiomyopathy (HP:0001638, 5/62, 4 NA, follow up: 1/5 resolved, 1/5 mild left ventricular dilatation, 3/5 unknown because they deceased), epileptic seizures (HP:0001250, 4/62, 4 NA), and further rare presentations (Figure 3E).

      Discussion

      The list of monogenetic diseases associated with pediatric ALF is expanding owing to the increasing availability and applicability of next-generation sequencing technologies. Within this patient group, pathogenic variants in genes pivotal for mitochondrial function are separately recognized because ALF can be the first symptom of a future multiorgan disease. Particularly, the risk of coexisting cardiomyopathy and cerebral involvement must be excluded when LTX is considered as rescue therapy for ALF. TRMU-associated ALF has been first described in 13 individuals in 2009.
      • Zeharia A.
      • Shaag A.
      • Pappo O.
      • et al.
      Acute infantile liver failure due to mutations in the TRMU gene.
      Subsequently, another 23 cases were described.
      • Schara U.
      • von Kleist-Retzow J.C.
      • Lainka E.
      • et al.
      Acute liver failure with subsequent cirrhosis as the primary manifestation of TRMU mutations.
      • Uusimaa J.
      • Jungbluth H.
      • Fratter C.
      • et al.
      Reversible infantile respiratory chain deficiency is a unique, genetically heterogenous mitochondrial disease.
      • Gaignard P.
      • Gonzales E.
      • Ackermann O.
      • et al.
      Mitochondrial infantile liver disease due to TRMU gene mutations: three new cases.
      • Taylor R.W.
      • Pyle A.
      • Griffin H.
      • et al.
      Use of whole-exome sequencing to determine the genetic basis of multiple mitochondrial respiratory chain complex deficiencies.
      • Grover Z.
      • Lewindon P.
      • Clousten A.
      • Shaag A.
      • Elpeleg O.
      • Coman D.
      Hepatic copper accumulation: a novel feature in transient infantile liver failure due to TRMU mutations?.
      • Indolfi G.
      • Iascone M.
      • Remaschi G.
      • et al.
      A child with ichthyosis and liver failure.
      • Gil-Margolis M.
      • Mozer-Glassberg Y.
      • Tobar A.
      • Ashkenazi S.
      • Zeharia A.
      • Marom D.
      [TRMU mutations – reversible infantile liver failure or multisystem disorder?].
      • Nicastro E.
      • Di Giorgio A.
      • Marchetti D.
      • et al.
      Diagnostic yield of an algorithm for neonatal and infantile cholestasis integrating next-generation sequencing.
      • Soler-Alfonso C.
      • Pillai N.
      • Cooney E.
      • Mysore K.R.
      • Boyer S.
      • Scaglia F.
      L-cysteine supplementation prevents liver transplantation in a patient with TRMU deficiency.
      • Kerr M.
      • Hume S.
      • Omar F.
      • et al.
      MITO-FIND: A study in 390 patients to determine a diagnostic strategy for mitochondrial disease.
      • Qin Z.
      • Yang Q.
      • Yi S.
      • Huang L.
      • Shen Y.
      • Luo J.
      Whole-exome sequencing identified novel compound heterozygous variants in a Chinese neonate with liver failure and review of literature.
      • Kose M.
      • Isik E.
      • Aykut A.
      • et al.
      The utility of next-generation sequencing technologies in diagnosis of Mendelian mitochondrial diseases and reflections on clinical spectrum.
      • Murali C.N.
      • Soler-Alfonso C.
      • Loomes K.M.
      • et al.
      TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.
      • Sala-Coromina J.
      • Miguel L.D.
      • de Las Heras J.
      • et al.
      Leigh syndrome associated with TRMU gene mutations.
      This study presents the largest reported cohort of 62 individuals with TRMU deficiency, summarizing the initial clinical presentations and long-term clinical course as well as all variants in TRMU associated with the disease. Still, cohort heterogeneity, sample size, and the retrospective nature of this study may limit the conclusions that can be draw from the data analysis.
      In translating our study results to practical, evidence-based recommendations, eg, when informing parents or setting up a treatment plan with the medical team for a newly diagnosed individual with TRMU deficiency, we can conclude that in most (40/62, 65%) individuals, TRMU-associated ALF is indeed a transient, reversible disease. Unfortunately, however, it led to death in more than a third of the affected individuals. Presence of LoF variants was a negative predictor for overall individual survival (Figure 1D). Furthermore, in this cohort, no episodes of ALF occurred after the first year of life.
      A possible explanation for this temporal presentation of ALF was provided recently by the demonstration that over the first year of life, some mitochondrial defects (including TRMU) can be metabolically compensated for by the activation of the cellular stress response and mTOR associated mitochondrial biogenesis.
      • Hathazi D.
      • Griffin H.
      • Jennings M.J.
      • et al.
      Metabolic shift underlies recovery in reversible infantile respiratory chain deficiency.
      This would support the hypothesis of cysteine supplementation therapy, which has shown benefits in anecdotal cases of TRMU deficiency disease.
      • Soler-Alfonso C.
      • Pillai N.
      • Cooney E.
      • Mysore K.R.
      • Boyer S.
      • Scaglia F.
      L-cysteine supplementation prevents liver transplantation in a patient with TRMU deficiency.
      ,
      • Murali C.N.
      • Soler-Alfonso C.
      • Loomes K.M.
      • et al.
      TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.
      Indeed, we found that supplementation with at least 1 cysteine source, NAC being the most frequently used in our cohort, improved survival significantly (level of evidence 1c, Figure 2A, survival probability in the first year with supplementation: 90%, without: 50%), particularly in the subgroup of individuals with predicted loss of protein function.
      Consequently, it is an evidence-based medicine level 1c recommendation to supplement with a cysteine source in any patient with TRMU deficiency at least in the first year. We further recommend considering NAC as the primary cysteine source given that it is thought to provide extended benefits for failing liver tissue by compensating for redox dysfunction (as commonly used in paracetamol-induced liver failure). We would further encourage consideration of supplementing NAC to all cases of suspected mitochondrial liver failure until TRMU-related disease has been excluded. However, conclusions on which cysteine source is the best and dosing and duration of supplementation cannot be drawn owing to the limited data availability. Further research is required to better understand the underlying pathophysiology and possible treatment options.
      On theoretical grounds, supplementation may only be necessary up to age 1 year. Interestingly, native liver survival (Figure 2F) seems unaffected by supplementation and the occurrence of ALF under supplementation may still require LTX because once the catastrophic cascade of hepatic necrosis is initiated, it seems not to be ameliorated by adding a cysteine sources. One could speculate that an earlier diagnosis and a consecutively early cysteine supplementation might improve outcome. We cannot arrive to a final conclusion based on our limited data. However, the survival of 2 individuals, diagnosed prenatally, who received early supplementation with cysteine suggests that this approach may lead to a better outcome.
      The decisions regarding necessity and timing of LTX remain specific to the clinical circumstances, but the fact that no ALF was reported after the age 1 year should be considered. Alternatively, progression of established ALF and worsening of hepatic encephalopathy with associated cerebral injury will eventually necessitate LTX.
      TRMU deficiency is predominantly a disease of the first year of life. Our cohort yielded multiorgan involvements but only in a minority of patients (Figure 3E). However, the most commonly reported during follow up in our cohort was neurodevelopmental delay. It is impossible to determine to what extent the neurodevelopmental delay is secondary to the liver failure or an unrelated clinical expression of mitochondrial disease. This also holds for the brain magnetic resonance imaging finding of bilateral hyperintensities in the basal ganglia as described in the article by Sala-Coromina et al.
      • Sala-Coromina J.
      • Miguel L.D.
      • de Las Heras J.
      • et al.
      Leigh syndrome associated with TRMU gene mutations.
      These were reported during ALF in 2 patients who died shortly afterwards. Hence, it is impossible to ascertain that this magnetic resonance imaging finding reflects the imaging of a vulnerable brain with mitochondrial dysfunction or whether this child would have progressed to the full picture of Leigh syndrome (subacute necrotizing encephalomyelopathy) in the strictest sense.
      • Rahman S.
      • Thorburn D.
      Nuclear gene-encoded Leigh syndrome spectrum overview.
      Given the rarity of TRMU deficiency, we advise that generally, there should be careful follow up of individuals in the first year by an experienced team at a specialized center with pediatric liver and mitochondrial disease specialists. Extended but regular follow-up visits with ultrasound examination of the liver and biochemical surveillance, including alpha-fetoprotein levels, should also exceed the first year of life. Furthermore, where clinically and genetically indicated, active consideration of LTX seems advisable.

      Data Availability

      Data will be supplied by the authors upon request.

      Conflict of Interest

      The authors declare no conflicts of interest.

      Acknowledgments

      The Chair in Genomic Medicine awarded to J.C. is generously supported by The Royal Children’s HospitalFoundation The Royal Children's Hospital Foundation . We are grateful to the Crane, Perkins, and Miller families for their generous financial support. We thank the Kinghorn Centre for Clinical Genomics for assistance with production and processing of genome sequencing data. This project was supported by the funding from MitoCanada (https://mitocanada.org) as part of the Mitochondrial Functional and Integrative Next Generation Diagnostics (MITO-FIND) study. This work was supported by the European Reference Network for Hereditary Metabolic Disorders (MetabERN). S.W. received funding from ERAPERMED2019-310 Personalized Mitochondrial Medicine (PerMiM): Optimizing diagnostics and treatment for patients with mitochondrial diseases FWF 4704-B. F.S.A. is funded by the National Institutes of Health along with the North American Mitochondrial Disease Consortia (5U54-NS078059-11), the Frontiers of Congenital Disorders of Glycosylation Consortia (FCDGC, 5U54-NS115198-02), Mervar Foundation, Courage for a Cure Foundation , PTC Therapeutics , Astellas Pharma Inc, and Saol Therapeutics. R.M. and R.W.T. are funded by the Wellcome Trust Centre for Mitochondrial Research (203105/Z/16/Z), the Mitochondrial Disease Patient Cohort (United Kingdom) (G0800674), the Medical Research Council International Centre for Genomic Medicine in Neuromuscular Disease (MR/S005021/1), the Medical Research Council (MR/W019027/1), the Lily Foundation , the UK NIHR Biomedical Research Centre for Ageing and Age-related Disease award to the Newcastle upon Tyne Hospitals NHS Foundation Trust , and the UK NHS Highly Specialised Service for Rare Mitochondrial Disorders of Adults and Children. R.W.T. also receives funding from the Pathological Society of Great Britain and Ireland. J.C. is supported by a New South Wales Office of Health and Medical Research Council Sydney Genomics Collaborative grant. We acknowledge funding from the National Health and Medical Research Council ( NHMRC ): project grant GNT1164479 (D.R.T.) and Principal Research Fellowship GNT1155244 (D.R.T.). The research conducted at the Murdoch Children’s Research Institute was supported by the Victorian Government’s Operational Infrastructure Support program. This study was supported by BMBF (German Federal Ministry of Education and Research ) through the German Network for Mitochondrial Diseases ([mitoNET] grant number 01GM1906B), Personalized Mitochondrial Medicine (PerMiM) (grant number 01KU2016A), and E-Rare project GENOMIT (grant number 01GM1207) and the Bavarian State Ministry of Health and Care within its framework of DigiMed Bayern (grant number DMB-1805- 0002). The authors extend their appreciation to the King Salman Center For Disability Research for funding this work through research group number RG-2022-010 (to F.S.A.)

      Author Information

      Conceptualization: G.F.V., S.W.; Data Curation: G.F.V., S.W., Y.M.-G., Y.E.L., R.G.F., J.A.M., H.B., L.D.S., H.Pr., A.Pec., F.S.A., J.J.B., G.B., I.B., N.B., B.B., J.C., E.C., D.C., A.M.D., N.D., A.D.M., F.D., E.A.E., M.E., W.F., P.G., R.D.G., E.G., C.H., J.H., V.K., M.Ko., M.Ke., A.K., D.L., R.M., M.G.M., K.Mo., T.M., K.Mu., E.N., A.Pen., H.Pe., D.P.-A., A.R., R.S., F.S., M.Sc., M.Shag., M.Shar., C.S.-A., C.S., I.S., M.St., R.W.T., D.R.T., E.L.T., J.-S.W., D.W.; Methodology: G.F.V., S.W., R.G.F., J.A.M.; Visualization: G.F.V., S.W., H.B., J.S.; Writing-original draft: G.F.V., S.W.; Writing-review and editing: G.F.V., S.W., Y.M.-G., Y.E.L., R.G.F., J.A.M., H.B., L.D.S., H.Pr., A.Pec., F.S.A., J.J.B., G.B., I.B., N.B., B.B., J.C., E.C., D.C., A.M.D., N.D., A.D.M., F.D., E.A.E., M.E., W.F., P.G., R.D.G., E.G., C.H., J.H., V.K., M.Ko., M.Ke., A.K., D.L., R.M., M.G.M., K.Mo., T.M., K.Mu., E.N., A.Pen., H.Pe., D.P.-A., A.R., R.S., F.S., M.Sc., M.Shag., M.Shar., C.S.-A., C.S., I.S., M.St., R.W.T., D.R.T., E.L.T., J.-S.W., D.W.

      Ethics Declaration

      This study was conducted in accordance with the guidelines of the Institutional Review Board of the Medical University of Innsbruck and the 1975 Declaration of Helsinki.
      • World Medical Association
      World Medical Association Declaration of Helsinki: ethical principles for medical research involving human subjects.
      Participants gave written informed consent for genetic investigations according to local regulations.

      Additional Information

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