- 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?
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.
What is basis for the name of this disease?
The name for this disease was coined by the French physicians Maroteaux and Lamy in 1962. They described the disorder in a report entitled "La pycnodysostose." (They were not the only discoverers of the disease. Andren and colleagues independently described the condition in 1962.) Maroteaux and Lamy put "pyknos," from the Greek meaning "dense" together with the compound word "dysostosis" meaning abnormal bone formation. The name "pycnodysostosis" was designed to convey the abnormally dense bone that is a hallmark of the disease.
Although the original Maroteaux and Lamy spelling was with a 'c', it has been written variably with a 'c' or a 'k'. Here we use the original spelling with a 'c'. No matter which way it is spelt, the name has stuck and is utilized worldwide today to designate this disease.
What are the characteristics of pycnodysostosis?
Pycnodysostosis causes abnormalities other than short stature, dense brittle bones, short fingers, and the wide open soft spot of the skull (see above). These other abnormalities involve the head and face, teeth, collar bones, skin, and nails. The front and back of the head are prominent. Within the open sutures of the skull, there may be many small bones (called wormian bones). The midface is less full than usual. The nose is prominent. The jaw can be small. The palate is narrow and grooved. The baby teeth are late coming in and may be lost much later than usual. The permanent teeth can also be slow to appear. The permanent teeth are commonly irregular and teeth may be missing (hypodontia). The collar bones are often underdeveloped and malformed. The skin over the back of the fingers is very wrinkled. The nails are flat and grooved.
Pycnodysostosis also causes problems that may become evident with time. Aside from the broken bones, the last bones of the fingers (the distal phalanges) and the collar bone can undergo slow progressive deterioration. Vertebral defects may permit the spine to curve laterally (resulting in scoliosis). The tooth problems often require orthodontic care and dental cavities are common.