ABSTRACT Hypophosphatasia is a rare inherited disorder characterized by defective skeletal mineralization and low alkaline phosphatase
activities in the serum. The genetic cause of hypophosphatasia is believed related to inactivating mutations in the TNSALP gene, encoding tissue-nonspecific alkaline phosphatase. Another rare inheritable disease, Saethre-Chotzen syndrome, leads
to premature fusion of the cranial sutures caused by heterozygous mutations of the human TWIST1 gene. Because the two disorders apparently are not genetically related (only reported individually) yet both involve defective
skeletal formation, we believe it is important to report our findings on a patient harboring mutations of TNSALP and TWIST1.