Which of the following describes hypophosphatasia?

• A. Rickets due to vitamin D deficiency
• B. Hypophosphatasia
• C. Osteoarthritis
• D. Gout

Answer: (B)

Hypophosphatasia is a genetic disorder of bone mineralization caused by reduced activity of tissue-nonspecific alkaline phosphatase. When this enzyme is low, inorganic pyrophosphate accumulates and inhibits the formation of hydroxyapatite, so bones and teeth don’t mineralize properly. This leads to rickets-like features in children and osteomalacia or fragility fractures in adults, often with very low alkaline phosphatase levels on lab testing. It’s distinct from rickets due to vitamin D deficiency, which involves a vitamin D pathway problem rather than ALP deficiency, and from osteoarthritis or gout, which are degenerative or inflammatory joint conditions not driven by impaired bone mineralization.