Hyperlysinemia, an ultrarare inborn error of metabolism: review and update

Familial hyperlysinemia is a rare autosomal recessive disorder due to defects of the AASS (α-aminoadipate δ-semialdehyde synthase) gene, which encodes for a bifunctional enzyme. Two types of hyperlysinemia have been identified namely type 1, due to the deficit of the alfa-ketoglutarate activity, and type 2, due to the deficit of the saccharopine dehydrogenase activity.