The protein encoded by this gene is a type II membrane protein that catalyzes the transfer of sialic acid from CMP-sialic acid to galactose-containing substrates. The encoded protein is normally found in the Golgi apparatus but can be proteolytically processed to a soluble form. This protein is a member of glycosyltransferase family 29. Mutations in this gene have been associated with autosomal recessive nonsymdromic mental retardation-12 (MRT12). Multiple transcript variants encoding several different isoforms have been found for this gene. [provided by RefSeq, Jul 2012].