Acute Strokelike Presentation and Long-term Evolution of Diffusion Restriction Pattern in Ethylmalonic Encephalopathy

Ethylmalonic Encephalopathy: a literature review and two new cases of mild phenotype

BACKGROUND

Ethylmalonic encephalopathy (EE) is a rare intoxication-type metabolic disorder with multisystem involvement. It is caused by mutations in ETHE1, which encodes the ETHE1 enzyme in the mitochondrial matrix that plays a key role in hydrogen sulfide (H2S) detoxification acting as a sulphur dioxygenase.

RESULTS

This review focuses on the clinical, metabolic, genetic and neuroradiological features of 70 reported cases, including two new cases. The common manifestations of EE are psychomotor regression, hypotonia, developmental delay, petechia, pyramidal signs, chronic diarrhoea, orthostatic acrocyanosis and failure to thrive, respectively. A significant difference was found in EMA and C4 levels (p=0.003, p=0.0236) between classical and mild phenotypes. Urinary EMA, C4 and C5 levels were found to exhibit normal values in milder cases during attack-free periods. The most common ETHE1 gene homozygous state mutations were (p.R163Q) (c.488G>A), exon 4 deletion, (p.R163W)(c.487C>T), (p.Glu44ValfsTer62)(c.131_132delAG) and (p.M1I)(c.3G>T) mutations, respectively. Fifty-two patients underwent cranial MRI. Basal ganglia signal alterations were detected in 42 cases. Of the 70 cases, eight had a mild phenotype and slow neurological progression with low levels of ethylmalonic acid (EMA) and C4 acylcarnitine. The current age of alive patients in the published articles with mild phenotype was significantly higher than the classical phenotype. (p=0.002). Reducing the accumulation and inducing detoxification of sulfide is the main long-term treatment strategy for EE, including metronidazole, N-acetylcysteine (NAC), dietary modification, liver transplantation and continuous renal replacement therapy (CRRT).

CONCLUSION

Measuring EMA and C4 acylcarnitine during metabolic attacks is critical to diagnosing EE, allowing for early treatment initiation to prevent further encephalopathic crises. Experience with liver transplantation, diet and CRRT, is currently limited. An early multidisciplinary approach with combination therapies is vital to prevent irreversible neurological damage.

Case Series of Ethylmalonic Encephalopathy from Southern India

Ethylmalonic encephalopathy is a rare neurometabolic disorder with central nervous system involvement and vasculopathy. It is presented in infancy with developmental delay, acrocyanosis, petechiae, chronic diarrhea, and early death. This was a retrospective study of confirmed cases of ethylmalonic aciduria from a tertiary care hospital over a period of 5 years from January 2015 to December 2020. Case details including analysis of clinical history, investigations, and outcomes are presented. Of six cases, male-to-female ratio was 4:2. Mean age of presentation was 35.5 months (range: 14-83 months). Consanguinity, global developmental delay, failure to thrive, skin rashes, microcephaly, hypotonia, and exaggerated deep tendon reflexes were observed in all cases. Chronic diarrhea was presented in five cases. The serum levels of C4 carnitine and urinary levels of ethylmalonic acid were increased in all cases. Magnetic resonance imaging (MRI) of the brain showed heterogenous bilateral symmetrical changes in the basal ganglia in five cases, and in one case, MRI could not be done. Genetic testing in two cases showed a homozygous variant in ETHE1 gene. Four children died, while the other two cases showed a decreased in recurrent encephalopathies and diarrhea after starting metronidazole. All children had global developmental delay, failure to thrive, skin rashes, central hypotonia, increased C4 carnitine levels in the serum, and increased ethylmalonic acid in the urine. Chronic diarrhea, acrocyanosis, and basal ganglia change in the MRI of the brain also give important clues for diagnosis. Metronidazole is useful in preventing recurrent episodes of encephalopathy.

An atypically mild case of ethylmalonic encephalopathy with pathogenic ETHE1 variant

Ethylmalonic encephalopathy (EE) is a rare, severe, autosomal recessive condition caused by pathogenic variants in ETHE1 leading to progressive encephalopathy, hypotonia evolving to dystonia, petechiae, orthostatic acrocyanosis, diarrhea, and elevated ethylmalonic acid in urine. In this case report, we describe a patient with only mild speech and gross motor delays, subtle biochemical abnormalities, and normal brain imaging found to be homozygous for a pathogenic ETHE1 variant (c.586G>A) via whole exome sequencing. This case highlights the clinical heterogeneity of ETHE1 mutations and the utility of whole-exome sequencing in diagnosing mild cases of EE.