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 1 inch). 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.


* Short stature * Craniofacial abnormalities * Delayed tooth eruption * Aplasia of clavicle * Scoliosis * Brachydactyly * Narrow ilia * Osteosclerosis * Increased bone density * Hypoplasia of clavicle * Osteomyelitis * Spondylolysis * Spondylolisthesis * Wrinkly skin on fingers * Grooves in nails * Flat nails * Irregular permanent teeth * Partial anodontia * Tooth caries


Pycnodysostosis is an autosomal recessive condition. It is autosomal in that the gene for pycnodysostosis is situated on one of the non- sex chromosomes (autosomes). Pycnodysostosis is recessive in that a single edition of the pycnodysostosis gene is not enough to cause the disease. Two copies of the abnormal gene (one from each parent) must be present for the disease to develop. The presence of a normal gene from one or both parents prevents the 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.