One Belgian neonate with the same c.334G > A (p.Gly112Ser) variant, as found in Patient 1, was reported to have a more severe perinatal form of HPP in 2004.[13] The mutation found in Patient 2 and his Korean father, c.1559delT (p.Leu520Argfs*86), is now well known as a common mutation in Japanese patients with HPP, with approximately 1/480 carriers in the Japanese population.[3] Many HPP patients harboring this mutation have shown phenotypes consistent with the perinatal lethal form,[14,15] and in vitro assays revealed significantly decreased activity of TNSALP.[16]. The gene discussed is ALPL; the disease is hypophosphatasia.