Child Neurology: Ethylmalonic encephalopathy

Ethylmalonic encephalopathy (EE; OMIM #602473) is an autosomal recessive disorder characterized by (1) progressive neurologic impairment, including global developmental delay with periods of regression during illness, progressive pyramidal and extrapyramidal signs, and seizures; and (2) generalized microvascular damage, including petechial purpura and chronic hemorrhagic diarrhea. It leads to premature death. EE is caused by mutations in ethylmalonic encephalopathy protein 1 ( ETHE1 ), and more than 60 different mutations have been reported.1,2 ETHE1 encodes a mitochondrial sulfur dioxygenase involved in the catabolism of hydrogen sulfide (H2S).2 Impairment of sulfur dioxygenase leads to the accumulation of hydrogen sulfide and its derivatives (thiosulphate) in various body fluids and tissues. Higher concentration of H2S is toxic and induces direct damage to cell membranes. It inhibits cytochrome c oxidase (COX), increases lactic acid and short-chain acyl-COA dehydrogenase, and leads to elevation of ethyl malonate and C4/C5 acylcarnitine in muscle and brain.2 We describe the clinical phenotype and MRI, pathologic, and biochemical findings of a patient with EE from India who had a novel homozygous c.493 G>C (p.D165H) variation in ETHE1 .