A case of ethylmalonic encephalopathy with atypical clinical and biochemical presentation.

A child is reported presenting with a clinical picture suggestive of genetic connective tissue disorders (vascular fragility, articular hyperlaxity, delayed motor development, and normal cognitive development), an absence of pathological ethylmalonic acid excretion during inter-critical phases and a homozygous R163W mutation in the ETHE1 gene. This case suggests that ethylmalonic aciduria is not a constant biochemical marker of ethylmalonic encephalopathy and that its normal excretion outside of metabolic decompensation episodes does not exclude this metabolic disease.