ALPL and hypophosphatasia: Hypophosphatasia (HPP) is a rare metabolic disorder resulting from a loss-of-function mutation in the ALPL gene with corresponding deficiency of tissue-nonspecific alkaline phosphatase (TNSALP) (Millán and Plotkin, 2012; Whyte et al., 2015; Yap and Savarirayan, 2016).