ST3GAL5 and GM3 synthase deficiency: The only known human disorder linked to abnormal SL biosynthesis is the human autosomal recessive infantile-onset symptomatic epilepsy syndrome (salt and pepper developmental regression syndrome; SPDRS) (OMIM 609056), which is a defect in ganglioside biosynthesis, caused by a nonsense mutation in the gene encoding sialyltransferase (GM3 synthase) (EC 2.4.99.9) [27].