GRB7 and Intellectual disability: Germline mutations of PGAP3 lead to a subtype of hyperphosphatemia and intellectual disabilities, also known as Mabry syndrome type 4.17 Kwon et al.18 have found that PGAP3 is co-amplified (together with STARD3, GRB7, and MIEN1) with ERBB2(Her2/neu) in esophageal and gastric cancer.