Intrafamilial phenotypic variability in hypophosphatasia: evidence from two families and the literature

Background Hypophosphatasia (HPP) is a genetic disorder caused by pathogenic mutations in the ALPL gene, resulting in reduced activity of the tissue-nonspecific alkaline phosphatase enzyme. The disease exhibits a wide phenotypic spectrum, varying from extremely severe forms that are often fatal during the prenatal or perinatal periods to very mild cases that are diagnosed in adult patients. Recent data indicate that familial cases account for approximately 50% of the total. Case presentation We