What Is Pycnodysostosis?

Pycnodysostosis, caused by mutations in the CTSK gene, is an inherited disorder that causes the bones to be abnormally dense (osteopetrosis). Individuals with this condition tend to be shorter than average and have certain bone deformities such as a curved spine (scoliosis), malformed collarbone, delayed closure of the skull plates, or shortened finger bones. The bones of individuals tend to be dense, but are brittle and can break easily while fractures of the legs, feet, jaws, and collar bones are common.

Pycnodysostosis can cause some characteristic facial features including a prominent nose, protruding forehead, prominent eyes, and small jaw. Sometimes the whites of eyes in individuals with pycnodysostosis can be tinted blue. Children with pycnodysostosis may have teeth that are late to grow, may be missing or irregular, and are prone to cavities.

How Common Is Pycnodysostosis?

Pycnodysostosis is a very rare disease. The prevalence of the disease is estimated to be rarer than 1 in 1,000,000 individuals.

How Is Pycnodysostosis Treated?

There is no treatment for the underlying cause of pycnodysostosis. Since the disease is so rare, treatments and therapies tend to be individualized. Some physicians may recommend injecting growth hormones to increase the height in individuals with pycnodysostosis. Surgery can help correct deformities of the face and jaw. Good dental hygiene and frequent visits to a dentist can be helpful as individuals with pycnodysostosis are prone to cavities and may be missing teeth. Orthodontia is also an option for improving the overall look of the teeth.

It is suggested that contact sports be avoided in order to minimize the chance of fracturing brittle bones. Exercise should be limited to low-impact sports such as swimming or cycling.

What Is the Prognosis for an Individual with Pycnodysostosis?

The prognosis for an individual with pycnodysostosis is generally good. While an individual with the condition may have a different appearance from individuals without the condition and be more prone to fractures, the lifespan is normal or near-normal with care.

Other names for

  • Maroteaux-Lamy syndrome
  • PKND
  • PYCD
  • Pyknodysostosis


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  • OMIM: Online Mendelian Inheritance In Man, OMIM [265800], 2014, https://www.omim.org/entry/265800
  • Xue et al., 2011, Orphanet J Rare Dis, 6:20, PMID: 21569238