Autosomal recessive OPA3 mutations have been identified in Iraqi Jewish patients presenting with Behr syndrome and 3-methylglutaconic aciduria (Costeff syndrome) [18] and more recently autosomal dominant [19] and recessive [20] OPA1 mutations were shown in Behr syndrome without metabolic abnormalities. Here, OPA3 is linked to 3-methylglutaconic aciduria.