SDHAF4 and hyperinsulinemic hypoglycemia, familial, 4: Interestingly, there are yet to be reports to establish a link between primary mitochondrial dysfunction and genetic defects involving the structural subunit SDHC or the assembly factors SDHAF2, SDHAF3 or SDHAF4. The results of the literature search into the genetic basis of mitochondrial complex II deficiency and the associated clinical phenotypes is presented below, stratified by causative SDHx gene.