A Synonymous Variant c.579A>G in the ETFDH Gene Caused Exon Skipping in a Patient With Late-Onset Multiple Acyl-CoA Dehydrogenase Deficiency: A Case Report

"Liver Failure in an Infant of Late-Onset Glutaric Aciduria Type II": Case Report

Glutaric aciduria type II, also known as Multiple acyl-CoA Dehydrogenase Deficiency, results from a defect in the mitochondrial electron transport chain resulting in an inability to break down fatty-acids and amino acids. There are three phenotypes- type 1 and 2 are of neonatal onset and severe form, with and without congenital anomalies, respectively, and presents with acidosis, severe hypotonia, cardiomyopathy, hepatomegaly, and non-ketotic hypoglycemia. Type 3 or late-onset Multiple acyl-CoA Dehydrogenase Deficiency usually presents in the adolescent or adult age group with phenotype ranging from mild forms of myopathy and exercise intolerance to severe forms of acute metabolic decompensation on its chronic course. Type 3 Multiple acyl-CoA Dehydrogenase Deficiency rarely presents in infancy and in liver failure. We present a five-month-old developmentally normal female child with acute encephalopathy, hypotonia, non-ketotic hypoglycemia, metabolic acidosis, and liver failure, with a history of sibling death of suspected inborn error of metabolism. The blood acyl-carnitine levels in Tandem Mass Spectrometry and urinary organic acid analysis through Gas Chromatography-Mass Spectrometry were unremarkable. The patient initially responded to riboflavin, CoQ, and supportive management but ultimately succumbed to sepsis with shock and multi-organ dysfunction. The clinical exome sequencing reported a homozygous missense variation in exon 11 of the ETFDH gene (chr4:g.158706270C > T) that resulted in the amino acid substitution of Leucine for Proline at codon 456 (p.Pro456Leu) suggestive of Glutaric aciduria type IIc (OMIM#231,680).

Multiple Acyl-Coenzyme A Dehydrogenase Deficiency Leading to Severe Metabolic Acidosis in a Young Adult

Background

Multiple acyl-coenzyme A dehydrogenase deficiency (MADD) is a rare metabolic disorder affecting fatty acid oxidation. Incidence at birth is estimated at 1:250 000, but type III presents in adults. It is characterized by nonspecific symptoms but if undiagnosed may cause ketoacidosis and rhabdomyolysis. A review of 350 patients found less than one third presented with metabolic crises. Our objective is to describe an adult with weakness after carbohydrate restriction that developed a pulmonary embolism and ketoacidosis, and was diagnosed with MADD type III.

Case Report

A 27-year-old woman with obesity presented to the hospital with fatigue and weakness worsening over months causing falls and decreased intake. She presented earlier to clinic with milder symptoms starting months after initiating a low carbohydrate diet. Testing revealed mild hypothyroidism and she started Levothyroxine for presumed hypothyroid myopathy but progressed. Muscle biopsy suggested a lipid storage myopathy. Genetic testing revealed a mutation in the ETFDH (electron transfer flavoprotein dehydrogenase) gene likely pathogenic for MADD; however, before this was available she developed severe ketoacidosis and rhabdomyolysis. She empirically started a low-fat diet, carnitine, cyanocobalamin, and coenzyme Q₁₀ supplementation with improvement. Over months her energy and strength normalized.

Discussion

MADD may cause ketoacidosis and rhabdomyolysis but this is rare in adults. Diagnosis requires clinical suspicion followed by biochemical and genetic testing. It should be considered when patients present with weakness or fasting intolerance. Treatment includes high carbohydrate, low-fat diets, supplementation, and avoiding fasting.

Conclusion

There should be greater awareness to consider MADD in adults presenting with neuromuscular symptoms, if untreated it may cause severe metabolic derangements.

Reclassification of a TMC1 synonymous substitution as a variant disrupting splicing regulatory elements associated with recessive hearing loss

Alterations of the transmembrane channel-like 1 gene (TMC1) are involved in autosomal recessive and dominant nonsyndromic hearing loss (NSHL). To date, up to 117 causal variants including substitutions, insertions and splice variants have been reported in families from different populations. In a patient suffering from severe prelingual NSHL, we identified, in the homozygous state, the previously considered likely benign synonymous c.627C>T; p.(Leu209=) substitution. We used in silico tools predicting variant-induced alterations of splicing regulatory elements (SREs) and pinpointed this transition as a candidate splice-altering variation. Functional splicing analysis, using a minigene assay, confirmed that the variant altered a critical regulatory sequence which is essential for the exon 11 inclusion in the TMC1 transcripts. This result was reinforced by the analysis of orthologous TMC1 mammalian sequences for which the deleterious effect on the mRNA processing of a native thymidine was always counteracted by the presence of a stronger donor splice site or additional enhancer motifs. This study demonstrates, for the first time, the pathogenicity of the c.627C>T alteration leading to its reclassification as a causal variant impacting SREs and highlights the major importance of exhaustive studies to accurately evaluate the pathogenicity of a variant, regardless of the variation type.

Clinical Presentations and Genetic Characteristics of Late-Onset MADD Due to ETFDH Mutations in Five Patients: A Case Series

Background: Late-onset multiple acyl-CoA dehydrogenase deficiency (LO-MADD) describes a curable autosomal recessive genetic disease caused by ETFDH mutations that result in defects in ETF-ubiquinone oxidoreductase. Almost all patients are responsive to riboflavin. This study describes the clinical presentations and genetic characteristics of five LO-MADD patients.

Methods: From 2018 to 2021, we collected clinical and genetic data on five patients diagnosed with LO-MADD at our hospital and retrospectively analyzed their clinical characteristics, laboratory examination, electromyography, muscle biopsy, genetic analysis, and outcome data.

Results: This study included three males and two females with mean onset age of 37.8 years. Fluctuating exercise intolerance was the most common presentation. Serum creatine kinase (CK) levels were significantly elevated in all patients, and plasma acylcarnitine profiles revealed an increase in long-chain acylcarnitine species in three cases. The urinary organic acid study revealed a high level of hydroxyglutaric acid in all patients. Electrophysiology demonstrated myogenic impairment. Muscle biopsies revealed lipid storage myopathy. Molecular analysis identified nine mutations (three novels and six reported) in ETFDH. Exercise intolerance and muscle weakness were dramatically improved in all patients treated with riboflavin (100 mg) daily following diagnosis.

Conclusions: LO-MADD is caused by ETFDH variants and responds well to riboflavin. Three novel ETFDH pathogenic variants were identified, expanding their spectrum in the Chinese population and facilitating future interpretation and analysis of ETFDH mutations.

ETF dehydrogenase advances in molecular genetics and impact on treatment

Electron transfer flavoprotein dehydrogenase, also called ETF-ubiquinone oxidoreductase (ETF-QO), is a protein localized in the inner membrane of mitochondria, playing a central role in the electron-transfer system. Indeed, ETF-QO mediates electron transport from flavoprotein dehydrogenases to the ubiquinone pool. ETF-QO mutations are often associated with riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency (RR-MADD, OMIM#231680), a multisystem genetic disease characterized by various clinical manifestations with different degrees of severity. In this review, we outline the clinical features correlated with ETF-QO deficiency and the benefits obtained from different treatments, such as riboflavin, L-carnitine and/or coenzyme Q10 supplementation, and a diet poor in fat and protein. Moreover, we provide a detailed summary of molecular and bioinformatic investigations, describing the mutations identified in ETFDH gene and highlighting their predicted impact on enzymatic structure and activity. In addition, we report biochemical and functional analysis, performed in HEK293 cells and patient fibroblasts and muscle cells, to show the relationship between the nature of ETFDH mutations, the variable impairment of enzyme function, and the different degrees of RR-MADD severity. Finally, we describe in detail 5 RR-MADD patients carrying different ETFDH mutations and presenting variable degrees of clinical symptom severity.

Hepatic Presentation of Late-Onset Multiple Acyl-CoA Dehydrogenase Deficiency (MADD): Case Report and Systematic Review

Diagnosis of pediatric steatohepatitis is a challenging issue due to a vast number of established and novel causes. Here, we report a child with Multiple Acyl-CoA Dehydrogenase Deficiency (MADD) presenting with an underrated muscle weakness, exercise intolerance and an atypically severe steatotic liver involvement. A systematic literature review of liver involvement in MADD was performed as well. Our patient is a 11-year-old otherwise healthy, non-obese, male child admitted for some weakness/asthenia, vomiting and recurrent severe hypertransaminasemia (aspartate and alanine aminotransferases up to ×20 times upper limit of normal). Hepatic ultrasound showed a bright liver. MRI detected mild lipid storage of thighs muscles. A liver biopsy showed a micro-macrovacuolar steatohepatitis with minimal fibrosis. Main causes of hypertransaminasemia were ruled out. Serum aminoacids (increased proline), acylcarnitines (increased C4-C18) and a large excretion of urinary glutaric acid, ethylmalonic, butyric, isobutyric, 2-methyl-butyric and isovaleric acids suggested a diagnosis of MADD. Serum acylcarnitines and urinary organic acids fluctuated overtime paralleling serum transaminases during periods of illness/catabolic stress, confirming their recurrent nature. Genetic testing confirmed the diagnosis [homozygous c.1658A > G (p.Tyr553Cys) in exon 12 of the ETFDH gene]. Lipid-restricted diet and riboflavin treatment rapidly ameliorated symptoms, hepatic ultrasonography/enzymes, and metabolic profiles. Literature review (37 retrieved eligible studies, 283 patients) showed that liver is an extramuscular organ rarely involved in late-onset MADD (70 patients), and that amongst 45 patients who had fatty liver only nine had severe presentation. Conclusion: MADD is a disorder with a clinically heterogeneous phenotype. Our study suggests that MADD warrants consideration in the work-up of obesity-unrelated severe steatohepatitis.