Gene : CTSK

What is Pycnodysostosis?

Pycnodysostosis is an inherited bone disorder that causes abnormally dense, brittle bones. This is due to a defective enzyme called cathepsin K. Because the bones are so brittle, bones of people with pycnodysostosis break easily. These breaks will typically occur in a person's legs, feet, jaw, and collar bone. Individuals with pycnodysostosis have short stature, as well as short fingers, a wide open soft spot on the skull, and characteristic facial features. Currently, there is no treatment that corrects the bone problems in individuals with pycnodysostosis; however, growth hormone replacement can be used to improve the height of these individuals. Also, plastic surgery can be used to correct the facial features. The life expectancy of people with this disorder is normal or nearly-normal. Pycnodysostosis is caused by pathogenic variants in the CTSK gene.

How is pycnodysostosis inherited?

Pycnodysostosis is inherited in an autosomal recessive manner. This type of inheritance requires the presence of two copies of a pathogenic variant in the gene for a person to have the genetic disease. Both parents must be carriers of a pathogenic variant in the gene in order to be at risk to have an affected child. The child must inherit a pathogenic variant from each carrier parent in order to be affected. There is a 1 in 4 chance that a baby will inherit two mutated copies of the gene and be affected when both parents are carriers.

What does it mean to be a carrier?

There are generally no signs or symptoms associated with being a carrier for pycnodysostosis. However, the risk to have a child affected with pycnodysostosis is increased. Testing of reproductive partners is recommended for carriers of pycnodysostosis.

How common is pycnodysostosis?

The population of pycnodysostosis is not known at this time. It is a very rare disorder.

Family References and Resources
Clinician References
What is Analyzed?
  • Full gene sequencing
Affected Systems


Carrier Rates
Detection Rate
Carrier Frequency
General Population > 99% 1 in 439

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