Hypophosphatasia: a rare genetic disorder that causes abnormal development of the teeth and bones. The abnormality is related to faulty mineralization, the process by which bones and teeth become strong due to their uptake of minerals like calcium and phosphorus. There are different forms of hypophosphatasia that vary in severity. The most severe form can cause stillbirth, while the mildest form results in the early loss of deciduous (baby) teeth without bone abnormalities. Hypophosphatasia is caused by mutations in a gene known as the tissue nonspecific alkaline phosphatase (ALPL) gene, also referred to as the TNSALP gene. Depending on the form of the condition, it can be inherited in both an autosomal dominant (meaning only one parent must carry the defective gene) or an autosomal recessive (meaning an affected person must receive a defective copy of the gene from each parent) pattern. Males and females are equally affected.