Mitochondrial complex II deficiency with multisystem involvement has been reported in association with biallelic SDHA [5], SDHB [2], SDHD [6, 7] and SDHAF1 [3, 8] gene variants, with clinical presentations including Leigh syndrome, leukoencephalopathy, optic atrophy and cardiomyopathy with highly variable severity and age of onset [5, 9]. Here, SDHD is linked to hyperinsulinemic hypoglycemia, familial, 4.