Pycnodysostosis (Pyknodysostosis)

  • Medical Reviewer: William C. Shiel Jr., MD, FACP, FACR
    William C. Shiel Jr., MD, FACP, FACR

    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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.

Medically Reviewed by a Doctor on 10/26/2016

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