ALPL and hypophosphatasia: Hypophosphatasia (HPP; OMIM#: 146300, 241500, 241510) is a rare inborn-error-of-metabolism that usually features rickets in children and osteomalacia in adults and is characterized by deficient tissue-nonspecific isozyme of alkaline phosphatase (TNALP), low serum alkaline phosphatase (ALP) activities, and defective bone and tooth mineralization.