GPC4 and hyperphosphatemia: For example, patients with phosphoglucomutase 3 (PGM3) deficiency exhibit severe combined immunodeficiency and skeletal dysplasia;189 patients with N-acetylgalactosaminyl transferase 3 (GALNT3) deficiency develop severe hyperphosphatemia, accompanied by paroxysmal bone pain, cortical hypertrophy and periosteal reaction;190 and genetic mutations in glypican 4 (GPC4), a member of the cell surface heparan sulfate proteoglycan family called Glypicans, can lead to Keipert syndrome, characterized by craniofacial and finger deformities.191