Hypophosphatasia (HPP) is a rare, inherited, systemic, metabolic disease caused by low tissue-nonspecific alkaline phosphatase (TNSALP) activity [1–5], which results in accumulation of the TNSALP substrates inorganic pyrophosphate (PPi) and pyridoxal 5′-phosphate (PLP) [6]. The gene discussed is ALPL; the disease is metabolic disease.