Pycnodysostosis (cont.)

Both pycnodysostosis and osteoporosis cause brittle bones. However, pycnodysostosis is a disease with abnormally dense bones, whereas osteoporosis is exactly the opposite, a disease with washed-out porous bones. There would seem to be no conceivable connection between pycnodysostosis and osteoporosis.

The new findings about cathepsin K and pycnodysostosis have made it clear that cathepsin K is a major protease in bone resorption. Given this function, it may well have a role in osteoporosis. Cathepsin K may, in fact, provide a rational basis for a new approach to the treatment of osteoporosis. This is an excellent illustration of how research on a rare disease may bring benefits to those affected by a common disease.

Bone fractures are a big problem for patients with pycnodysostosis. They can occur with minimal stress. It is important that the disease be diagnosed and the tendency to fractures be recognized so that (1) fractures can be minimized, if not entirely prevented; and (2) the parents and other caregivers are not falsely accused of child abuse! As with any condition causing brittle bones, the infant should be handled with a reasonable degree of care. The older child should be encouraged to engage in safer forms of exercise such as swimming rather than, for example, jumping on a trampoline.

In 1996, Soliman and colleagues reported that there is defective secretion of growth hormone in pycnodysostosis. Replacement treatment with growth hormone was then tested. It was found to increase the growth of the length of bones (linear growth). Since short stature is an important consequence of pycnodysostosis, growth hormone treatment may prove very useful.