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Correspondence and requests for materials should be addressed to Georg F. Vogel, Department of Paediatrics I, Innsbruck Medical University, Anichstrasse 35, 6020 Innsbruck, Austria
Department of Paediatrics I, Medical University of Innsbruck, Innsbruck, AustriaInstitute of Cell Biology, Biocenter, Medical University of Innsbruck, Innsbruck, Austria
Metabolism Service, Schneider Children’s Medical Center of Israel, Petah Tiqwa, IsraelSackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
Institute of Human Genetics, School of Medicine, Technical University of Munich, Munich, GermanyInstitute of Neurogenomics, Computational Health Center, Helmholtz Zentrum München, Neuherberg, Germany
Institute of Human Genetics, School of Medicine, Technical University of Munich, Munich, GermanyInstitute of Neurogenomics, Computational Health Center, Helmholtz Zentrum München, Neuherberg, Germany
Division of Neuropaediatrics and Metabolic Medicine, Center for Paediatric and Adolescent Medicine, University Hospital Heidelberg, Heidelberg, GermanyInstitute of Human Genetics, Heidelberg University, Heidelberg, Germany
Department of Medical Genetics and Reference Center for Mitochondrial Diseases (CARAMMEL), Necker Hospital, Université Paris Cité, Paris, FranceInstitut Imagine, INSERM UMR 1163, Paris, France
Brain and Mitochondrial Research Group, Murdoch Children’s Research Institute, Melbourne, Victoria, AustraliaDepartment of Paediatrics, The University of Melbourne, Melbourne, Victoria, Australia
Department of Pediatric Neurology, Centre for Neuromuscular Disorders, Centre for Translational Neuro- und Behavioral Sciences, University Duisburg-Essen, Essen, Germany
Department of Pediatrics, Division of Pediatric Metabolism, University of Health Sciences, Bakırkoy Dr. Sadi Konuk Training and Research, Istanbul, Turkey
Department of Biochemistry, Reference Center for Mitochondrial Disease, FILNEMUS, Bicêtre University Hospital, University of Paris-Saclay, Assistance Publique-Hôpitaux de Paris, Le Kremlin-Bicêtre, Paris, France
Department of Pediatrics, University of Pennsylvania Perelman School of Medicine, Philadelphia, PAMitochondrial Medicine Frontier Program, Division of Human Genetics, Department of Pediatrics, Children’s Hospital of Philadelphia, Philadelphia, PA
Pediatric Hepatology and Pediatric Liver Transplantation Unit, Reference Center for Mitochondrial Disease, FILNEMUS, Bicêtre University Hospital, University of Paris-Saclay, Assistance Publique-Hôpitaux de Paris, Le Kremlin-Bicêtre, Paris, FranceInserm U1193, Hepatinov, University Paris-Saclay, Orsay, Paris, France
Division of Inborn Errors of Metabolism, Department of Pediatrics, İzmir Katip Çelebi University, Izmir, TurkeyDivision of Genetics, Department of Pediatrics, Ege University, Izmir, Turkey
Discovery DNA, Metabolics and Genetics in Canada (M.A.G.I.C.) Clinic Ltd, Department of Pediatrics, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
Discovery DNA, Metabolics and Genetics in Canada (M.A.G.I.C.) Clinic Ltd, Department of Pediatrics, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
Division of Neuropaediatrics and Metabolic Medicine, Center for Paediatric and Adolescent Medicine, University Hospital Heidelberg, Heidelberg, Germany
Wellcome Centre for Mitochondrial Research, Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, United KingdomNHS Highly Specialised Service for Rare Mitochondrial Disorders, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, United Kingdom
Department of Medical Genetics and Reference Center for Mitochondrial Diseases (CARAMMEL), Necker Hospital, Université Paris Cité, Paris, FranceInstitut Imagine, INSERM UMR 1163, Paris, France
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TXTexas Children’s Hospital, Houston, TXJoint BCM-CUHK Center of Medical Genetics, Prince of Wales Hospital, Shatin, Hong Kong SAR
Department of Medical Genetics and Reference Center for Mitochondrial Diseases (CARAMMEL), Necker Hospital, Université Paris Cité, Paris, FranceInstitut Imagine, INSERM UMR 1163, Paris, FranceReference Center of Inherited Metabolic Disorders, Necker Hospital, Université Paris Cité, Paris, France
Department of Liver & Small Bowel Health Centre King Faisal Specialist Hospital & Research Center, Riyadh, Saudi ArabiaCollege of Medicine, Alfaisal University, Riyadh, Saudi Arabia
Division of Neuropaediatrics and Metabolic Medicine, Center for Paediatric and Adolescent Medicine, University Hospital Heidelberg, Heidelberg, Germany
Wellcome Centre for Mitochondrial Research, Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, United KingdomNHS Highly Specialised Service for Rare Mitochondrial Disorders, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, United Kingdom
Brain and Mitochondrial Research Group, Murdoch Children’s Research Institute, Melbourne, Victoria, AustraliaDepartment of Paediatrics, The University of Melbourne, Melbourne, Victoria, Australia
University Children's Hospital, Salzburger Landeskliniken and Paracelsus Medical University, Salzburg, AustriaAmalia Children’s Hospital, Radboudumc, Nijmegen, The Netherlands
This study aimed to define the genotypic and phenotypic spectrum of reversible acute liver failure (ALF) of infancy resulting from biallelic pathogenic TRMU variants and determine the role of cysteine supplementation in its treatment.
Methods
Individuals with biallelic (likely) pathogenic variants in TRMU were studied within an international retrospective collection of de-identified patient data.
Results
In 62 individuals, including 30 previously unreported cases, we described 47 (likely) pathogenic TRMU variants, of which 17 were novel, and 1 intragenic deletion. 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 was a transient, reversible disease and cysteine supplementation improved survival.
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 (IMD) 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 they bridge the diagnostic gap in >30% of the cases that remain unsolved after the application of conventional diagnostics.
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. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
In that original patient cohort of 13 individuals, 4 died of ALF; however, 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,
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.
Therefore, L-cysteine or N-acetylcysteine (NAC) have been supplemented in individuals with TRMU deficiency, and anecdotal case reports showed beneficial effects.
TRMU deficiency is a disorder of the mitochondrial transcript processing and mitochondrial tRNA modification category (international classification of IMD
). 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.
Material and Methods
Study design and data acquisition
Individuals were included based on an international retrospective collection of de-identified data. Inclusion criteria were presence of rare biallelic variants in TRMU classified as likely pathogenic or pathogenic according to the American College of Medical Genetics and Genomics guidelines.
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.
Regarding standards of evidence for therapeutic studies, we used the grading system from the Centre for Evidence-Based Medicine (http://www.cebm.net, eg, level 1c = “All or None” which means [prolongation of] survival with therapy).
American College of Medical Genetics and Genomics classification
The meta tool REVEL that combines SIFT, PolyPhen-2, HVAR and HDIV, LRT, Mutation Taster, Mutation Assessor, FATHMM v2.3, and VEST 3.0 was used for PP3 scoring. If the result of the REVEL prediction was pathogenic, 4 points in PP3 were given. All analyzed variants were identified to be either pathogenic or uncertain using REVEL. PP4 was applied to all variants because of the highly specific clinical features, with the exception of p.(Gly272Asp) in patient 52 (no liver involvement reported). Four points were given for PS3 if tRNA metabolism was analyzed and altered. Two points for PS3 were given if OXPHOS enzyme activity was reduced. Criteria for PP5 were not met. For all variants the following reference sequences were used: NM_018006.5, NP_060476.2 and NC_000022.11.
In silico modeling of TRMU missense variant pathogenicity scores
To assess the predicted effect of missense variants, commonly used prediction scores (M-CAP v.3.5a and REVEL v.3.5a
) were annotated for all biologically possible TRMU missense variants and mapped onto a linearized representation of the TRMU protein, as previously demonstrated.
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, Vienna, Austria) ggplot2 package to plot a smoothened line and CI.
Statistics and software
Kaplan-Meier estimators 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. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
Zeharia A, Shaag A, Pappo O, et al. Acute infantile liver failure due to mutations in the TRMU gene. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
Zeharia A, Shaag A, Pappo O, et al. Acute infantile liver failure due to mutations in the TRMU gene. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
Zeharia A, Shaag A, Pappo O, et al. Acute infantile liver failure due to mutations in the TRMU gene. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
Zeharia A, Shaag A, Pappo O, et al. Acute infantile liver failure due to mutations in the TRMU gene. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
Zeharia A, Shaag A, Pappo O, et al. Acute infantile liver failure due to mutations in the TRMU gene. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
Zeharia A, Shaag A, Pappo O, et al. Acute infantile liver failure due to mutations in the TRMU gene. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
Zeharia A, Shaag A, Pappo O, et al. Acute infantile liver failure due to mutations in the TRMU gene. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
Zeharia A, Shaag A, Pappo O, et al. Acute infantile liver failure due to mutations in the TRMU gene. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
Zeharia A, Shaag A, Pappo O, et al. Acute infantile liver failure due to mutations in the TRMU gene. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
The version number for each transcript is omitted, however it can be cross referenced from Table 2. Variants presented in bold are novel. Four points for PP4 were given for all cases except for patient 52 (no liver involvement reported) because the clinical features were highly characteristic for all patients included in the study. Four points were given for PS3 if transfer RNA metabolism was analyzed and altered. Two points for PS3 were given if OXPHOS enzyme activity was reduced. If the result of the REVEL prediction was pathogenic, 4 points were given in PP3. The following reference numbers were used for all variants: NM_018006.5, NP_060476.2 and NC_000022.11.
ACMG, American College of Medical Genetics and Genomics; bp, basepair; gnomAD, Genome Aggregation Database; LoF, loss of function; LPTH, likely pathogenic; PTH, pathogenic.
Zeharia A, Shaag A, Pappo O, et al. Acute infantile liver failure due to mutations in the TRMU gene. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
Zeharia A, Shaag A, Pappo O, et al. Acute infantile liver failure due to mutations in the TRMU gene. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
Zeharia A, Shaag A, Pappo O, et al. Acute infantile liver failure due to mutations in the TRMU gene. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
Zeharia A, Shaag A, Pappo O, et al. Acute infantile liver failure due to mutations in the TRMU gene. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
Zeharia A, Shaag A, Pappo O, et al. Acute infantile liver failure due to mutations in the TRMU gene. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
Zeharia A, Shaag A, Pappo O, et al. Acute infantile liver failure due to mutations in the TRMU gene. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
Zeharia A, Shaag A, Pappo O, et al. Acute infantile liver failure due to mutations in the TRMU gene. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
Zeharia A, Shaag A, Pappo O, et al. Acute infantile liver failure due to mutations in the TRMU gene. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
Zeharia A, Shaag A, Pappo O, et al. Acute infantile liver failure due to mutations in the TRMU gene. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
Zeharia A, Shaag A, Pappo O, et al. Acute infantile liver failure due to mutations in the TRMU gene. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
Zeharia A, Shaag A, Pappo O, et al. Acute infantile liver failure due to mutations in the TRMU gene. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
Unpublished individuals are presented in bold. Loss of function variants are marked with an asterisk. L-TRMU nomenclature reflects cases with only published data available. The following reference numbers were used for all variants: NM_018006.5, NP_060476.2 and NC_000022.11.
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. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
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 47 different variants were identified; of these, 17 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 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 for all potential TRMU missense variants using REVEL score. D. LoF variants (red) influence survival probability of individuals with TRMU deficiency in comparison with Kaplan-Meier estimator. 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 an increased density in the catalytic domain near the interaction site 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) detected in 16 and 13 individuals, respectively. As expected, variants showed comparable REVEL scores throughout the gene with fewer variants in the C-terminal region of the protein (Figure 1C). The 17 loss-of-function (LoF) variants and the intragenic deletion predicted to lead to loss of protein were detected at least in monoallelic state in 23 individuals. Presence of a LoF variant strongly affected on overall individual survival (P = .0089) (Figure 1D). Overall survival did not differ between individuals having a LoF variant in 1 allele only and those having it in both the 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 (IQR = 13.8) months. 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 2Individual survival and hepatic phenotype. A. Supplementation therapy (red) influences survival probability of individuals with TRMU deficiency in comparison with Kaplan-Meier estimator. 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 (red) and without (blue) LTX therapy is compared using Kaplan-Meier estimator. ALF, acute liver failure; LTX, liver transplantation; suppl, supplementation.
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 the 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 (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
North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition position paper on the diagnosis and management of pediatric acute liver failure.
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 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: 1 during surgery because of variceal bleeding and the other one shortly after LTX because of 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 3Native liver survival, liver histology, clinical presentation, and course of TRMU-related symptoms. A. Supplementation therapy (blue) does not influence native liver survival, eg, the need for liver transplantation, in comparison with Kaplan-Meier estimator. B. Most prevalent findings in liver histopathology. C. Common clinical presentation in 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 to develop 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. Am J Hum Genet. 2009;85(3):401-407. Published correction appears in Am J Hum Genet. 2010;86(2):295. https://doi.org/10.1016/j.ajhg.2009.08.004
This study now presented 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 drawn 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.
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; however, the fact that no ALF was reported after 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 study by Sala-Coromina et al.
These were reported during ALF in 2 patients who died shortly afterward. 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.
TRMU deficiency was shown to have a specific clinical phenotype of an infantile onset (when survived) reversible, isolated ALF and can be distinguished from its differential diagnoses that encompass several other IMDs. In contrast to TRMU deficiency, individuals with DGUOK deficiency often already have liver cirrhosis upon presentation and do not show a reversible phenotype. In individuals with NBAS deficiency, the reversible ALF periods are related to febrile infections.
Individuals with LARS1 deficiency are characterized by recurrent elevation of liver transaminases up to liver failure and multisystem involvement (abnormalities of growth, blood, nervous system, muscles).
Given the rarity of TRMU deficiency, we generally advise that 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, we suggest that, 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 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.
Funding
This project was supported by the funding from MitoCanada (https://mitocanada.org) as part of the MITO-FIND study. This work was supported by the European Reference Network for Hereditary Metabolic Disorders (MetabERN). S.W. 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. 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 mitoNET German Network for Mitochondrial Diseases (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.)
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.
This article is not retracted. It has been withdrawn at the request of the authors as it was noted there were inaccuracies in variant classification in the published manuscript. These inaccuracies did not substantially change the results or conclusions of the original paper. The variant classification has been corrected and the article will be republished shortly.
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