ALPL and hypophosphatasia: Hypophosphatasia (HPP; OMIM #241500, 241510, 146300), which was first reported by the Canadian pediatrician John Campbell Rathbun in 1948, is a systemic bone disease caused by the deficiency of tissue-nonspecific alkaline phosphatase (TNAP).37Mutations resulting in reduced activity of TNSALP are associated with abnormal bone mineralization.