AASS and glutaryl-CoA dehydrogenase deficiency: AASS is a bifunctional enzyme with two domains: the lysine-ketoglutarate reductase (LKR) that converts lysine to saccharopine and the saccharopine dehydrogenase (SDH) that oxidizes saccharopine to α-AASA.12 Patients with mutations in the LKR domain specifically have a benign biochemical disorder of hyperlysinaemia.13,14 Furthermore, pre-clinical studies have demonstrated the utility of inhibiting AASS for other disorders of lysine metabolism such as glutaric aciduria type I.15