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Achondroplasia is a disorder of bone growth that causes the most common type of dwarfism.
Achondroplasia is one of a group of disorders called chondrodystrophies or osteochondrodysplasias.
Achondroplasia may be inherited as an autosomal dominant trait, which means that if a child gets the defective gene from one parent, the child will have the disorder. 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%.
However, most cases appear as spontaneous mutations. This means that two parents without achondroplasia may give birth to a baby with the condition.
The typical appearance of achondroplastic dwarfism can be seen at birth. Symptoms may include:
During pregnancy, a prenatal ultrasound may show excessive amniotic fluid surrounding the unborn infant.
Examination of the infant after birth shows increased front-to-back head size. There may be signs of hydrocephalus ("water on the brain").
X-rays of the long bones can reveal achondroplasia in the newborn.
There is no specific treatment for achondroplasia. Related abnormalities, including spinal stenosis and spinal cord compression, should be treated when they cause problems.
People with achondroplasia seldom reach 5 feet in height. Intelligence is in the normal range. Infants who receive the abnormal gene from both parents do not often live beyond a few months.
If there is a family history of achondroplasia and you plan to have children, you may find it helpful to speak to your health care provider.
Genetic counseling may be helpful for prospective parents when one or both have achondroplasia. However, because achondroplasia most often develops spontaneously, prevention is not always possible.
Horton WA, Hecht JT. Disorders involving transmembrane receptors. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 687.