Hypophosphatasia is a skeletal dysplasia affecting the gene ALPL, which codes for tissue non-specific alkaline phosphatase. As alkaline phosphatase is responsible for the mineralization of the skeleton, any detrimental changes to its structure and function will delay skeletal development.

This disease is characterized by widespread non-ossification of the skeleton, leading to brittle bones and fracturing in utero. The presence of Bowdler spurs help to differentiate hypophosphatasia from other disorders of ossification.

The radiograph shows moderate micromelemia, with asymmetric bowing of proximal long bones and prominent fracturing. Note the metaphyses are largely unaffected. The distal long bones are erratic and symmetrically bowed, with irregular ossification and Bowdler spurs, which are easily discerned in gross images.

There is non-ossification of pelvic or pubic bones with the exception of the ilia. There is very little ossification of phalanges or metacarpals. The ribs are very short, and the thoracic cage is narrow as a result.

There is non-ossification of pedicles in both the thoracic and lumbar spine, typical of this disorder. The subject displays characteristic deficient calvarial ossification with non-ossification of much of the skull, leading to caput membranaceum in utero.

A radiograph of the subject’s sibling (gestational age: 22 weeks) with the same mutation is included in related content. Its skeleton is far less affected, illustrating the disease’s wide spectrum of severity.

This image shows a specimen photograph of the legs. See related content for frontal view radiograph and specimen photograph.