Most patients suffering from hereditary sensory and autonomic neuropathy type 1 (HSAN1) carry mutations in SPTLC1 or SPTLC2. These mutations do not affect the activity of the SPT-complex, but instead shift its substrate affinity so that in addition to canonical SPT products, cytotoxic 1-deoxysphingolipids are formed through the incorporation of L-alanine instead of L-serine. The gene discussed is AGXT; the disease is hereditary sensory and autonomic neuropathy type 1.