GPC5 and autism: Moreover, a genetic association has been found between autism and the HS3ST5 gene encoding one of the HS 3-O sulfotransferases in two cohorts of European ancestry49, and a genome-wide scan in 996 cases with autism identified four independent CNVs in the GPC5/GPC6 gene cluster50, which encodes the glypicans 5 and 6, two members of a family of glycosylphosphatidylinositol-anchored HS proteoglycans.