Late onset of symptoms in an atypical patient with the cblJ inborn error of vitamin B12 metabolism: Diagnosis and novel mutation revealed by exome sequencing

► This paper describes a third patient with the cblJ inborn error of metabolism. ► The patient presented with methylmalonic aciduria and homocystinuria. ► Clinical and in vitro studies suggested a less severe form of the disorder. ► Studies of cellular cobalamin metabolism were inconclusive. ► Exome sequencing demonstrated a homozygous mutation (c.423C>G) in the ABCD4 gene.