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Synonyms of Pyknodysostosis

  • PKND
  • PYCD
  • Pycnodysostosis

Disorder Subdivisions

  • No subdivisions found.

General Discussion

Pyknodysostosis is a rare disorder that is inherited as an autosomal recessive genetic trait. This disorder is characterized by short stature, increased bone density (osteosclerosis/osteopetrosis), underdevelopment of the tips of fingers with absent or small nails, fragile bones that may fracture easily, abnormal or absent collarbone (clavicle), and skull abnormalities with a protruding forehead and bulge on the back of the skull caused by delayed suture closure.


Pyknodysostosis is a rare disorder characterized by short stature and increased density of the bones. Individuals with this disorder typically have short arms and legs, an abnormal collarbone, and distinctive facial features including a large head with a small face, small chin, underdeveloped facial bones, a high forehead, high narrow palate and dental abnormalities. Bone fractures are common in individuals with pyknodysostosis. The small jaw may predispose affected individuals to periods of not breathing during sleep (obstructive sleep apnea).


The gene for PKND has been mapped to the same location as the gene for cathepsin K on chromosome 1q21. Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated "p" and a long arm designated "q". Chromosomes are further sub-divided into many bands that are numbered. For example, "chromosome1q21" refers to band 21 on the long arm of chromosome 1. The numbered bands specify the location of the thousands of genes that are present on each chromosome.

Pyknodysostosis is a rare disorder that is inherited as an autosomal recessive genetic trait. Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother.

Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%. The risk is the same for males and females.

All individuals carry 4-5 abnormal genes. Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.

Affected Populations

Pyknodysostosis is a very rare disorder that affects males and females in equal numbers. There have been approximately 133 cases of this disorder reported in the medical literature.

Related Disorders

Symptoms of the following disorders can be similar to those of Pyknodysostosis. Comparisons may be useful for a differential diagnosis:

Cleidocranial dysplasia is a rare disorder characterized by premature closure of the soft spot on the head (coronal) causing the forehead to bulge outward and a wide face. A delay in closure of the space between the bones of the skull (fontanels) is also present. Complete or partial absence of the collarbone and narrow drooping shoulders are also apparent in patients with this disorder. Delayed eruption of teeth, moderately short stature, a high arched palate, a wide pelvis joint, failure of the lower jaw joints to unite, and fingers that are irregular in length may also be present. (For more information on this disorder, choose "cleidocranial dysplasia" as your search term in the Rare Disease Database.)

Osteopetrosis is a combination of several genetically caused symptoms grouped together as one disorder. It can be inherited as either a dominant or recessive trait and is marked by increased bone density, brittle bones, and in some cases, skeletal abnormalities. Although symptoms may not initially be apparent in people with mild forms of this disorder, trivial injuries may cause bone fractures due to abnormalities of the bone. (For more information on this disorder, choose "osteopetrosis" as your search term in the Rare Disease Database.)

Osteogenesis imperfecta, or brittle bone disease, is a group of hereditary connective tissue disorders characterized by unusual bone fragility and tendency to fracture bones easily. There are at least four distinct forms of the disorder, representing extreme variation in severity from one individual to another. Osteogenesis Imperfecta Congenita is apparent at birth, while Osteogenesis Imperfecta Tarda manifests itself later in life and is a milder disease. (For more information on this disorder, choose "osteogenesis imperfecta" as your search term in the Rare Disease Database.)

Standard Therapies

The diagnosis of pyknodysostosis is based on physical features and X-ray findings. Molecular genetic testing is available to identify abnormalities in the cathepsin K gene.

Individuals with pyknodysostosis will need orthopedic care when fractures occur. Appropriate dental care should be provided and craniofacial surgery may be warranted.
Treatment may be required to relieve the obstructive sleep apnea.

Genetic counseling may be of benefit for patients and their families. Other treatment is symptomatic and supportive.

Investigational Therapies

Information on current clinical trials is posted on the Internet at All studies receiving U.S. government funding, and some supported by private industry, are posted on this government website.

For information about clinical trials being conducted at the National Institutes of Health (NIH) in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222
TTY: (866) 411-1010

For information about clinical trials sponsored by private sources, contact:

Pyknodysostosis Resources

NORD Member Organizations:

(To become a member of NORD, an organization must meet established criteria and be approved by the NORD Board of Directors. If you're interested in becoming a member, please contact Susan Olivo, Membership Manager, at

Other Organizations:


Harris, M. Pyknodysostosis. In: The NORD Guide to Rare Disorders, Philadelphia: Lippincott, Williams and Wilkins, 2003:242-243.

Gorlin RJ, Cohen MM, Levin LS. Syndromes of the head and neck, 3rd ed. Oxford: Oxford University Press, 1990:285-287.

McKusick VA, ed. Online Mendelian Inheritance in Man (OMIM). Baltimore, MD: The Johns Hopkins University; Entry No. 265800; Last Update: 9/17/03.

Gelb BD, Shi GP, Chapman, et al. Pycnodysostosis, a lysosomal disease caused by cathepsin K deficiency. Science 1996;273:1236-1238.

Hunt NP, Cunningham SJ Adnan N, et al. The dental, craniofacial, and biochemical features of pyknodysostosis: a report of three cases. L Oral Maxillofac Surg 1998;56:497-504.

Polymeropoulos MH, Ortiz De Luna RI, Ide SE, et al. The gene for pyknodysostosis maps to human chromosome 1cen-g21. Nature Genet. 1995;10:238-239.

The information in NORD’s Rare Disease Database is for educational purposes only. It should never be used for diagnostic or treatment purposes. If you have questions regarding a medical condition, always seek the advice of your physician or other qualified health professional. NORD’s reports provide a brief overview of rare diseases. For more specific information, we encourage you to contact your personal physician or the agencies listed as “Resources” on this report.

Report last updated: 2008/03/31 00:00:00 GMT+0

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