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Definition
Achondroplasia is a disorder of bone growth that causes the most common type of dwarfism.Causes, incidence, and risk factors
Achondroplasia is an inherited disorder of bone growth. It is one of the group of disorders that are collectively called chondrodystrophies or osteochondrodysplasias.
The disorder causes a type of dwarfism that is recognized by its characteristic normal to large-sized head, shortened arms and legs (especially the upper arm and thigh), a normal-sized trunk, and waddling gait. Achondroplasia is the most common type of dwarfism.
Achondroplasia can be inherited as an autosomal dominant trait, which means that if a child gets the defective gene from one parent, he or she will have the disorder.
However, the majority of cases, approximately 80%, appear as spontaneous mutations. This means that two patients without achondroplasia may give birth to a baby with achondroplasia. If one parent has achondroplasia, the infant has a 50% chance of inheriting the disorder. If both parents have the condition, the infant's chances of being affected increase to 75%.
Symptoms
Typical appearance of achondroplastic dwarfism is apparent at birth:Notes: A family history of achondroplasia should alert parents to the possibility of having an affected child.
Signs and tests
Examination of the infant shows increased front-to-back head size (occipital-frontal circumference). There may be signs of hydrocephalus associated with enlargement of the chambers within the center of the brain (ventricular dilatation).
X-rays of the long bones can demonstrate achondroplasia in the newborn.
Treatment
There is no specific treatment for achondroplasia. Associated orthopedic abnormalities such as club feet should be corrected.Expectations (prognosis)
People with achondroplasia seldom reach five feet in height. Intelligence is in the normal range. Infants who are homozygous for achondroplasia (both parents are achondroplastic and each has contributed an affected gene) seldom live beyond a few months.
Complications
Calling your health care provider
Call for an appointment with your health care provider if you are planning to have children and there is a family history of achondroplasia.
Prevention
Genetic counseling may be helpful for prospective parents when one or both have achondroplasia. Because achondroplasia usually arises as a spontaneous mutation, however, prevention is not always possible.
Update Date: 2/12/2003 Updated by: Andrew L. Chen, M.D., M.S., Department of Orthopaedic Surgery, Hospital for Joint Diseases, New York, NY. Review provided by VeriMed Healthcare Network.
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Page last updated: 28 October 2004 |