Exome sequence analysis also identified gain of function variants in in the serine palmitoyltransferase long chain base subunit 1 (SPTLC1) and serine palmitoyltransferase long chain base subunit 2 (SPTLC2) genes as causative for both MacTel2 and hereditary sensory and autonomic neuropathy type 1 (HSAN-1), an extremely rare neurologic disease. The gene discussed is SPTLC2; the disease is hereditary sensory and autonomic neuropathy type 1.