 On the other hand, GPC1, GPC2, GPC4, and GPC6 have between 35% and 63% sequence similarity.Thus, GPC3 and GPC5 are often referred to as one subfamily of glypicans, with GPC1, GPC2, GPC4, and GPC6 constituting the other group.Between the subfamilies of glypicans, there is about 25% sequence similarity.