The c.1660C>T p.(Arg554Trp) SDHA substitution was described in two sisters born to consanguineous Algerian parents who both presented at 10 months of age with developmental regression and whose MRI imaging were consistent with a clinical diagnosis of Leigh syndrome (Cases 30 and 31,Table 1) [21,30]; this case report represents the inaugural genetic diagnosis of Mendelian mitochondrial respiratory chain disease in man. Here, SDHA is linked to Leigh syndrome.