Medical Reviewer:

Pycnodysostosis facts

  • Pycnodysostosis is an inherited disorder of the bone.
  • Pycnodysostosis causes short stature.
  • Pycnodysostosis causes abnormally dense brittle bones.
  • Pycnodysostosis causes the "soft spot" of a baby's skull to stay widely open.
  • Pycnodysostosis is due to a defect in an enzyme: cathepsin K.
  • Growth hormone treatment may increase growth in pycnodysostosis.

What is pycnodysostosis?

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Pycnodysostosis is perhaps best known as the diagnosis given retrospectively to the late 19th century French artist Henri de Toulouse-Lautrec (portrayed by Jose Ferrer in the 1952 film "Moulin Rouge").

Pycnodysostosis is a genetic (inherited) disease of the bone. Its pattern of inheritance follows the classic rules of genetics (see below).

Pycnodysostosis consistently causes short stature. The height of adult males with the disease is less than 150 cm (59 inches, or 4 feet 11 inches). Adult females with pycnodysostosis are even shorter.

Pycnodysostosis causes the bones to be abnormally dense (osteosclerosis); the last bones of the fingers (the distal phalanges) to be unusually short; and delays the normal closure of the connections (sutures) of the skull bones in infancy, so that the "soft spot" (the fontanel) on top of the head remains widely open.

Pycnodysostosis causes brittle bones which easily break (fracture). The bones in the legs and feet tend to fracture. The jaw and collar bone (clavicles) are also particularly prone to fractures.

The precise frequency of pycnodysostosis has never been determined. Pycnodysostosis can be classified in the large group of genetic diseases that are individually uncommon, but collectively important because of the sum of their numbers, their heavy impact upon affected individuals, and the equally heavy burden they place upon their families.

Medically Reviewed by a Doctor on 4/13/2015

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