What is the most characteristic consequence of hypophosphatasia?

• A. Defective mineralization of bone and teeth.
• B. Hypermineralization of bone.
• C. Increased osteoclast activity.
• D. Increased bone density.

Answer: (A)

Defective mineralization of bone and teeth: Hypophosphatasia results from mutations that reduce tissue-nonspecific alkaline phosphatase activity. Without enough ALP, inorganic pyrophosphate accumulates and strongly inhibits hydroxyapatite formation, so bone and dental matrices fail to mineralize properly. Clinically, this leads to soft, poorly mineralized bones (rickets in children, osteomalacia in adults) and dental problems such as premature loss of teeth due to defective cementum. This is why defective mineralization is the defining consequence, rather than hypermineralization, increased osteoclast activity, or increased bone density.