Novel ECHS1 mutation in an Emirati neonate with severe metabolic acidosis

Loss of mitochondrial fatty acid β-oxidation protein short-chain Enoyl-CoA hydratase disrupts oxidative phosphorylation protein complex stability and function

Short-chain enoyl-CoA hydratase 1 (ECHS1) is involved in the second step of mitochondrial fatty acid β-oxidation (FAO), catalysing the hydration of short-chain enoyl-CoA esters to short-chain 3-hyroxyl-CoA esters. Genetic deficiency in ECHS1 (ECHS1D) is associated with a specific subset of Leigh Syndrome, a disease typically caused by defects in oxidative phosphorylation (OXPHOS). Here, we examined the molecular pathogenesis of ECHS1D using a CRISPR/Cas9 edited human cell 'knockout' model and fibroblasts from ECHS1D patients. Transcriptome analysis of ECHS1 'knockout' cells showed reductions in key mitochondrial pathways, including the tricarboxylic acid cycle, receptor-mediated mitophagy and nucleotide biosynthesis. Subsequent proteomic analyses confirmed these reductions and revealed additional defects in mitochondrial oxidoreductase activity and fatty acid β-oxidation. Functional analysis of ECHS1 'knockout' cells showed reduced mitochondrial oxygen consumption rates when metabolising glucose or OXPHOS complex I-linked substrates, as well as decreased complex I and complex IV enzyme activities. ECHS1 'knockout' cells also exhibited decreased OXPHOS protein complex steady-state levels (complex I, complex III₂ , complex IV, complex V and supercomplexes CIII₂ /CIV and CI/CIII₂ /CIV), which were associated with a defect in complex I assembly. Patient fibroblasts exhibit varied reduction of mature OXPHOS complex steady-state levels, with defects detected in CIII₂ , CIV, CV and the CI/CIII₂ /CIV supercomplex. Overall, these findings highlight the contribution of defective OXPHOS function, in particular complex I deficiency, to the molecular pathogenesis of ECHS1D.

ECHS1 deficiency and its biochemical and clinical phenotype

ECHS1 gene encodes a mitochondrial enzyme, short-chain enoyl-CoA hydratase (SCEH). SCEH is involved in fatty acid oxidation ([Sharpe and McKenzie (2018); Mitochondrial fatty acid oxidation disorders associated with short-chain enoyl-CoA hydratase (ECHS1) deficiency, 7: 46]) and valine catabolism ([Fong and Schulz (1977); Purification and properties of pig heart crotonase and the presence of short chain and long chain enoyl coenzyme A hydratases in pig and guinea pig tissues, 252: 542-547]; [Wanders et al. (2012); Enzymology of the branched-chain amino acid oxidation disorders: The valine pathway, 35: 5-12]), and the dysfunction of SCEH leads to a severe Leigh or Leigh-like Syndrome phenotype in patients ([Haack et al. (2015); Deficiency of ECHS1 causes mitochondrial encephalopathy with cardiac involvement, 2: 492-509]; [Peters et al. (2014); ECHS1 mutations in Leigh disease: A new inborn error of metabolism affecting valine metabolism, 137: 2903-2908]; [Sakai et al. (2015); ECHS1 mutations cause combined respiratory chain deficiency resulting in Leigh syndrome, 36: 232-239]; [Tetreault et al. (2015); Whole-exome sequencing identifies novel ECHS1 mutations in Leigh, 134: 981-991]). This study aims to further describe the ECHS1 deficiency phenotype using medical history questionnaires and standardized tools assessing quality of life and adaptive skills. Our findings in this largest sample of ECHS1 patients in literature to date (n = 13) illustrate a severely disabling condition causing severe developmental delays (n = 11), regression (n = 10), dystonia/hypotonia and movement disorders (n = 13), commonly with symptom onset in infancy (n = 10), classical MRI findings involving the basal ganglia (n = 11), and variability in biochemical profile. Congruent with the medical history, our patients had significantly low composite and domain scores on Vineland Adaptive Behavior Scales, Third Edition. We believe there is an increasing need for better understanding of ECHS1 deficiency with an aim to support the development of transformative genetic-based therapies, driven by the unmet need for therapies for patients with this genetic disease.

Clinical improvements after treatment with a low-valine and low-fat diet in a pediatric patient with enoyl-CoA hydratase, short chain 1 (ECHS1) deficiency

Background

Enoyl-CoA hydratase short-chain 1 (ECHS1) is a key mitochondrial enzyme that is involved in valine catabolism and fatty acid beta-oxidation. Mutations in the ECHS1 gene lead to enzymatic deficiency, resulting in the accumulation of certain intermediates from the valine catabolism pathway. This disrupts the pyruvate dehydrogenase complex and the mitochondrial respiratory chain, with consequent cellular damage. Patients present with a variable age of onset and a wide spectrum of clinical features. The Leigh syndrome phenotype is the most frequently reported form of the disease. Herein, we report a case of a male with ECHS1 deficiency who was diagnosed at 8 years of age. He presented severe dystonia, hyperlordosis, moderate to severe kyphoscoliosis, great difficulty in walking, and severe dysarthria. A valine-restricted and total fat-restricted diet was considered as a therapeutic option after the genetic diagnosis. An available formula that restricted branched-chain amino acids and especially restricted valine was used. We also restricted animal protein intake and provided a low-fat diet that was particularly low in dairy fat.

Results

This protein- and fat-restricted diet was initiated with adequate tolerance and adherence. After three years, the patient noticed an improvement in dystonia, especially in walking. He currently requires minimal support to walk or stand. Therefore, he has enhanced his autonomy to go to school or establish a career for himself. His quality of life and motivation for treatment have greatly increased.

Conclusions

There is still a substantial lack of knowledge about this rare disorder, especially knowledge about future effective treatments. However, early diagnosis and treatment with a valine- and fat-restricted diet, particularly dairy fat-restricted diet, appeared to limit disease progression in this patient with ECHS1 deficiency.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02468-6.

Deciphering the molecular landscape of microcephaly in 87 Indian families by exome sequencing

Microcephaly is a frequent feature of neurodevelopmental disorders (NDDs). Our study presents the heterogeneous spectrum of genetic disorders in patients with microcephaly either in isolated form or in association with other neurological and extra-neural abnormalities. We present data of 91 patients from 87 unrelated families referred to our clinic during 2016-2020 and provide a comprehensive clinical and genetic landscape in the studied cohort. Molecular diagnosis using exome sequencing was made in 45 families giving a yield of 51.7%. In 9 additional families probable causative variants were detected. We identified disease causing variations in 49 genes that are involved in different functional pathways Among these, 36 had an autosomal recessive pattern, 8 had an autosomal dominant pattern (all inherited de novo), and 5 had an X-linked pattern. In 41 probands where sequence variations in autosomal recessive genes were identified 31 were homozygotes (including 16 from non-consanguineous families). The study added 28 novel pathogenic/likely pathogenic variations. The study also calls attention to phenotypic variability and expansion in spectrum as well as uncovers genes where microcephaly is not reported previously or is a rare finding. We here report phenotypes associated with the genes for ultra-rare NDDs with microcephaly namely ATRIP, MINPP1, PNPLA8, AIMP2, ANKLE2, NCAPD2 and TRIT1.

Whole-exome sequencing identified novel variants in three Chinese Leigh syndrome pedigrees

Leigh syndrome (LS), the most common mitochondrial disease in early childhood, usually manifests variable neurodegenerative symptoms and typical brain magnetic resonance imaging (MRI) lesions. To date, pathogenic variants in more than 80 genes have been identified. However, there are still many cases without molecular diagnoses, and thus more disease-causing variants need to be unveiled. Here, we presented three clinically suspected LS patients manifesting neurological symptoms including developmental delay, hypotonia, and epilepsy during the first year of age, along with symmetric brain lesions on MRI. We explored disease-associated variants in patients and their nonconsanguineous parents by whole-exome sequencing and subsequent Sanger sequencing verification. Sequencing data revealed three pairs of disease-associated compound heterozygous variants: c.1A>G (p.Met1?) and 409G>C (p.Asp137His) in SDHA, c.1253G>A (p.Arg418His) and 1300C>T (p.Leu434Phe) in NARS2, and c.5C>T (p.Ala2Val) and 773T>G (p.Leu258Trp) in ECHS1. Among them, the likely pathogenic variants c.409G>C (p.Asp137His) in SDHA, c.1300C>T (p.Leu434Phe) in NARS2, and c.773T>G (p.Leu258Trp) in ECHS1 were newly identified. Segregation analysis indicated the possible disease-causing nature of the novel variants. In silico prediction and three-dimensional protein modeling further suggested the potential pathogenicity of these variants. Our discovery of novel variants expands the gene variant spectrum of LS and provides novel evidence for genetic counseling.

Exploring triheptanoin as treatment for short chain enoyl CoA hydratase deficiency

We explored the benefits of triheptanoin as a treatment for Short Chain Enoyl Co‐A Hydratase (SCEH) deficiency. One child with early onset, severe SCEH Deficiency was treated with triheptanoin, an odd chain oil with anapleurotic properties, for 37 months. Blood and urine chemistry safety measures, motor skills assessment, physical exam, and neurological assessment were monitored over a 27 month period. Modest sustained gains in motor skills, attention, muscle bulk, and strength were observed without any significant adverse effects. Triheptanoin appears to be a promising effective treatment for SCEH Deficiency.

Delineating the neurological phenotype in children with defects in the ECHS1 or HIBCH gene

The neurological phenotype of 3-hydroxyisobutyryl-CoA hydrolase (HIBCH) and short-chain enoyl-CoA hydratase (SCEH) defects is expanding and natural history studies are necessary to improve clinical management. From 42 patients with Leigh syndrome studied by massive parallel sequencing, we identified five patients with SCEH and HIBCH deficiency. Fourteen additional patients were recruited through collaborations with other centres. In total, we analysed the neurological features and mutation spectrum in 19 new SCEH/HIBCH patients. For natural history studies and phenotype to genotype associations we also included 70 previously reported patients. The 19 newly identified cases presented with Leigh syndrome (SCEH, n = 11; HIBCH, n = 6) and paroxysmal dystonia (SCEH, n = 2). Basal ganglia lesions (18 patients) were associated with small cysts in the putamen/pallidum in half of the cases, a characteristic hallmark for diagnosis. Eighteen pathogenic variants were identified, 11 were novel. Among all 89 cases, we observed a longer survival in HIBCH compared to SCEH patients, and in HIBCH patients carrying homozygous mutations on the protein surface compared to those with variants inside/near the catalytic region. The SCEH p.(Ala173Val) change was associated with a milder form of paroxysmal dystonia triggered by increased energy demands. In a child harbouring SCEH p.(Ala173Val) and the novel p.(Leu123Phe) change, an 83.6% reduction of the protein was observed in fibroblasts. The SCEH and HIBCH defects in the catabolic valine pathway were a frequent cause of Leigh syndrome in our cohort. We identified phenotype and genotype associations that may help predict outcome and improve clinical management.

Phenotypic spectrum of short-chain enoyl-Coa hydratase-1 (ECHS1) deficiency

INTRODUCTION

ECHS1 encodes for short-chain enoyl-CoA hydratase, a key component in b-oxidation. This enzyme is also involved in the isoleucine and valine catabolic pathways. The literature contains reports of scattered cases of ECHS1 mutation, which show a wide clinical spectrum of presentation. Despite that the clinical spectrum of the disease has not been defined so far due to the absence of previous systematic reviews and descriptions of large series of patients.

METHODS

We performed a systematic literature review of so far reported ECHS1 mutated patients and we reported two additional cases. We pointed out clinical and neuroradiological features of all patients.

RESULTS

45 patients were included in the analysis. Based on clinical and neuroradiological feature we were able to distinguish four main phenotypes of ECHS1deficiency: a severe neonatal presentation with a rapid and fatal course and significant white matter abnormalities; a severe infantile variant with slower neurological deterioration, developmental delay, pyramidal and extrapyramidal signs, optic atrophy, feeding difficulties, and degeneration of the deep gray nuclei; a slowly progressive infantile form, qualitatively similar to the previous phenotype, but less severe with mainly basal ganglia involvement; and a final phenotype, present in only few cases, characterized by paroxysmal exercise-induced dystonic attacks, normal neurological examination between these episodes, and isolated pallidal degeneration on MRI.

INTERPRETATION

ECHS1 mutations cause metabolic encephalopathy with a wide range of clinical presentations that can be grouped into four main phenotypes, each with a distinct profile in terms of severity on clinical presentation, disease course and MRI involvement.

Clinical, biochemical and metabolic characterization of patients with short-chain enoyl-CoA hydratase(ECHS1) deficiency: two case reports and the review of the literature

BACKGROUND

Short-chain enoyl-CoA hydratase (SCEH or ECHS1) deficiency is a rare congenital metabolic disorder caused by biallelic mutations in the ECHS gene. Clinical phenotype includes severe developmental delay, regression, dystonia, seizures, elevated lactate, and brain MRI abnormalities consistent with Leigh syndrome (LS). SCEH is most notably involved in valine catabolism. There is no effective treatment for the disease, patients may respond to dietary restriction of valine and supplementation of N-acetylcysteine .

CASE PRESENTATION

We describe two patients who presented in infancy or early childhood with SCEH deficiency. Both patients were shown to harbor heterozygous or homozygous variants in the ECHS1 gene, and developmental retardation or regression as the onset manifestation. Brain MRI showed abnormal signals of bilateral pallidus. Urine metabolic examination showed increased levels of 2,3-dihydroxy-2-methylbutyric acid and S-(2-carboxypropyl) cysteamine S-(2-carboxypropoxypropyl) cysteamine (SCPCM). A valine restricted diet and combined of N-acetylcysteine supplementation were utilized in the two patients.

CONCLUSIONS

In clinical practice, The elevated urinary 2,3-dihydroxy-2-methylbutyrate, S-(2-carboxypropyl) cysteine, S-(2-carboxypropyl) cysteine and N-acetyl-S-(2-carboxypropyl) cysteine levels might be clues for diagnosis of SCEH deficiency which can be confirmed throughGenetic sequencing of ECHS1 gene. Early cocktail therapy, valine restrictied diet and N-acetylcysteine supplementation could improve the prognosis of patients.

Understanding the role of OXPHOS dysfunction in the pathogenesis of ECHS1 deficiency

Mitochondria provide the main source of energy for eukaryotic cells, oxidizing fatty acids and sugars to generate ATP. Mitochondrial fatty acid β-oxidation (FAO) and oxidative phosphorylation (OXPHOS) are two key pathways involved in this process. Disruption of FAO can cause human disease, with patients commonly presenting with liver failure, hypoketotic glycaemia and rhabdomyolysis. However, patients with deficiencies in the FAO enzyme short-chain enoyl-CoA hydratase 1 (ECHS1) are typically diagnosed with Leigh syndrome, a lethal form of subacute necrotizing encephalomyelopathy that is normally associated with OXPHOS dysfunction. Furthermore, some ECHS1-deficient patients also exhibit secondary OXPHOS defects. This sequela of FAO disorders has long been thought to be caused by the accumulation of inhibitory fatty acid intermediates. However, new evidence suggests that the mechanisms involved are more complex, and that disruption of OXPHOS protein complex biogenesis and/or stability is also involved. In this review, we examine the clinical, biochemical and genetic features of all ECHS1-deficient patients described to date. In particular, we consider the secondary OXPHOS defects associated with ECHS1 deficiency and discuss their possible contribution to disease pathogenesis.

An incidental finding in newborn screening leading to the diagnosis of a patient with ECHS1 mutations

Short-chain enoyl-CoA hydratase (ECHS1) is a mitochondrial beta-oxidation enzyme involved in the metabolism of acyl-CoA fatty acid esters, as well as in valine metabolism. ECHS1 deficiency has multiple manifestations, including Leigh syndrome early at birth or in childhood with poor prognosis, to cutis laxa, exercise-induced dystonia and congenital lactic acidosis.

Here we describe the case of a newborn with mutations in ECHS1 that caught our attention after the incidental finding of 3-hydroxy-butyryl\3-hydroxy-isobutyryl\malonylcarnitine (C4OH\C3DC) and tiglylcarnitine (C5:1) on blood spot in the newborn screening (NBS) program. Diagnosis was suspected based on the analysis of organic acids on dried urine spot. A moderate increase of 2-methyl-2,3-dihydroxybutyric acid, was detected, which is a known marker of this disease. Exome analysis showed c.404A>G (p.Asn135Ser) mutation in homozygosis in the ECHS1 gene. The child was therefore admitted to the hospital. Initial examination showed little response to auditory stimuli and mild hypertonia of the extremities. Clinical deterioration was evident at 4 months of age, including neurological and cardiac involvement, and the patient died at 5 months of age. This case illustrates how an incidental detection in the NBS Program can lead to the diagnosis ECHS1 deficiency. Although it is a severe disease, with no treatment available, early detection would allow adequate genetic counseling avoiding the odyssey that suffered most of these families.

Comparative Analysis of Mitochondrial Proteome Reveals the Mechanism of Enhanced Ram Sperm Motility Induced by Carbon Ion Radiation After In Vitro Liquid Storage

The aim of this study was to reveal the mechanism of enhanced ram sperm motility induced by heavy ion radiation (HIR) after in vitro liquid storage. Ram semen was stored for 24 hours at 5°C and then irradiated with 0.1 Gy carbon ion radiation (CIR). In comparison to nonirradiated (NIR) sperm, the motility, viability, and adenosine triphosphate content were all higher in CIR sperm, and the reactive oxygen species levels were lower. Moreover, 87 differential mitochondrial protein spots were detected in 2-dimensional gels between CIR and NIR sperm and were identified as 52 corresponding proteins. In addition, 33 differential proteins were involved in a main pathway network, including COX5B, ERAB/HSD17B10, ETFA, SDHB, and SOD2, which are known to be involved in cell communication, energy production, and antioxidant responses. We used immunoblotting and immunofluorescence to analyze the content and localization of these proteins, respectively, and the levels of these proteins in CIR sperm were lower than those in NIR sperm. An understanding of the molecular function of these proteins could provide further insight into the mechanisms underlying high sperm motility induced by HIR in rams.

Extrapolation of Variant Phase in Mitochondrial Short-Chain Enoyl-CoA Hydratase (ECHS1) Deficiency

Loss-of-function and hypomorphic ECHS1 variants are associated with mitochondrial short-chain enoyl-CoA hydratase deficiency, an inborn error of valine metabolism. We report an 8-year-old boy with developmental delay, ataxia, hemiplegia, and hearing loss with abnormalities in the basal ganglia. Biochemical studies were essentially normal except for a persistent mildly elevated CSF alanine. This patient demonstrates an intermediate phenotype between a Leigh-like, early-onset presentation and paroxysmal exercise-induced dyskinesia. Two novel ECHS1 variants (c.79T>G; p.Phe27Val and c.789_790del; p.Phe263fs) were identified via exome sequencing in the proband, and pathogenicity was confirmed by enzyme assay performed on patient fibroblasts. Neither of the ECHS1 variants detected in the child were present in the mother. However, due to nearby polymorphisms, it was possible to determine that p.Phe263fs occurred de novo on the maternal chromosome and that p.Phe27Val likely derived from the paternal chromosome. Nearby polymorphisms can help set phase of variants when only a single parent is available for testing or when an identified variant occurs de novo.

Mitochondrial Fatty Acid Oxidation Disorders Associated with Short-Chain Enoyl-CoA Hydratase (ECHS1) Deficiency

Mitochondrial fatty acid β-oxidation (FAO) is the primary pathway for fatty acid metabolism in humans, performing a key role in liver, heart and skeletal muscle energy homeostasis. FAO is particularly important during times of fasting when glucose supply is limited, providing energy for many organs and tissues, including the heart, liver and brain. Deficiencies in FAO can cause life-threatening metabolic disorders in early childhood that present with liver dysfunction, hypoglycemia, dilated hypertrophic cardiomyopathy and Reye-like Syndrome. Alternatively, FAO defects can also cause ‘milder’ adult-onset disease with exercise-induced myopathy and rhabdomyolysis. Short-chain enoyl-CoA hydratase (ECHS1) is a key FAO enzyme involved in the metabolism of fatty acyl-CoA esters. ECHS1 deficiency (ECHS1D) also causes human disease; however, the clinical manifestation is unlike most other FAO disorders. ECHS1D patients commonly present with Leigh syndrome, a lethal form of subacute necrotizing encephalomyelopathy traditionally associated with defects in oxidative phosphorylation (OXPHOS). In this article, we review the clinical, biochemical and genetic features of the ESHS1D patients described to date, and discuss the significance of the secondary OXPHOS defects associated with ECHS1D and their contribution to overall disease pathogenesis.

Clinical, biochemical, and genetic features of four patients with short-chain enoyl-CoA hydratase (ECHS1) deficiency

Short-chain enoyl-CoA hydratase (SCEH or ECHS1) deficiency is a rare inborn error of metabolism caused by biallelic mutations in the gene ECHS1 (OMIM 602292). Clinical presentation includes infantile-onset severe developmental delay, regression, seizures, elevated lactate, and brain MRI abnormalities consistent with Leigh syndrome (LS). Characteristic abnormal biochemical findings are secondary to dysfunction of valine metabolism. We describe four patients from two consanguineous families (one Pakistani and one Irish Traveler), who presented in infancy with LS. Urine organic acid analysis by GC/MS showed increased levels of erythro-2,3-dihydroxy-2-methylbutyrate and 3-methylglutaconate (3-MGC). Increased urine excretion of methacrylyl-CoA and acryloyl-CoA related metabolites analyzed by LC-MS/MS, were suggestive of SCEH deficiency; this was confirmed in patient fibroblasts. Both families were shown to harbor homozygous pathogenic variants in the ECHS1 gene; a c.476A > G (p.Gln159Arg) ECHS1variant in the Pakistani family and a c.538A > G, p.(Thr180Ala) ECHS1 variant in the Irish Traveler family. The c.538A > G, p.(Thr180Ala) ECHS1 variant was postulated to represent a Canadian founder mutation, but we present SNP genotyping data to support Irish ancestry of this variant with a haplotype common to the previously reported Canadian patients and our Irish Traveler family. The presence of detectable erythro-2,3-dihydroxy-2-methylbutyrate is a nonspecific marker on urine organic acid analysis but this finding, together with increased excretion of 3-MGC, elevated plasma lactate, and normal acylcarnitine profile in patients with a Leigh-like presentation should prompt consideration of a diagnosis of SCEH deficiency and genetic analysis of ECHS1. ECHS1 deficiency can be added to the list of conditions with 3-MGA.

Mitochondrial Encephalopathy and Transient 3-Methylglutaconic Aciduria in ECHS1 Deficiency: Long-Term Follow-Up

We report the major diagnostic challenge in a female patient with signs and symptoms suggestive of an early-onset mitochondrial encephalopathy. Motor and cognitive development was severely delayed and brain MRI showed signal abnormalities in the putamen and caudate nuclei. Metabolic abnormalities included 3-methylglutaconic aciduria and elevated lactate levels in plasma and cerebrospinal fluid, but were transient. Whole exome sequencing at the age of 25 years finally revealed compound heterozygous mutations c.[229G>C];[563C>T], p.[Glu77Gln];[Ala188Val] in the ECHS1 gene. Activity of short-chain enoyl-CoA hydratase, a mitochondrial enzyme encoded by the ECHS1 gene, was markedly decreased in lymphocytes. Retrospective urine analysis confirms that elevated levels of S-(2-carboxypropyl)cysteamine, S-(2-carboxypropyl)cysteine, and N-acetyl-S-(2-carboxypropyl)cysteine can be a diagnostic clue in the disease spectrum of ECHS1 mutations.

Lethal neonatal case and review of primary short-chain enoyl-CoA hydratase (SCEH) deficiency associated with secondary lymphocyte pyruvate dehydrogenase complex (PDC) deficiency

Mutations in ECHS1 result in short-chain enoyl-CoA hydratase (SCEH) deficiency which mainly affects the catabolism of various amino acids, particularly valine. We describe a case compound heterozygous for ECHS1 mutations c.836T>C (novel) and c.8C>A identified by whole exome sequencing of proband and parents. SCEH deficiency was confirmed with very low SCEH activity in fibroblasts and nearly absent immunoreactivity of SCEH. The patient had a severe neonatal course with elevated blood and cerebrospinal fluid lactate and pyruvate concentrations, high plasma alanine and slightly low plasma cystine. 2-Methyl-2,3-dihydroxybutyric acid was markedly elevated as were metabolites of the three branched-chain α-ketoacids on urine organic acids analysis. These urine metabolites notably decreased when lactic acidosis decreased in blood. Lymphocyte pyruvate dehydrogenase complex (PDC) activity was deficient, but PDC and α-ketoglutarate dehydrogenase complex activities in cultured fibroblasts were normal. Oxidative phosphorylation analysis on intact digitonin-permeabilized fibroblasts was suggestive of slightly reduced PDC activity relative to control range in mitochondria. We reviewed 16 other cases with mutations in ECHS1 where PDC activity was also assayed in order to determine how common and generalized secondary PDC deficiency is associated with primary SCEH deficiency. For reasons that remain unexplained, we find that about half of cases with primary SCEH deficiency also exhibit secondary PDC deficiency. The patient died on day-of-life 39, prior to establishing his diagnosis, highlighting the importance of early and rapid neonatal diagnosis because of possible adverse effects of certain therapeutic interventions, such as administration of ketogenic diet, in this disorder. There is a need for better understanding of the pathogenic mechanisms and phenotypic variability in this relatively recently discovered disorder.