Achondroplasia

• Causes, incidence, and risk factors

  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.

• Symptoms

  The typical appearance of achondroplastic dwarfism can be seen at birth. Symptoms may include:

  • Abnormal hand appearance with persistent space between the long and ring fingers
  • Bowed legs
  • Decreased muscle tone
  • Disproportionately large head-to-body size difference
  • Prominent forehead (frontal bossing)
  • Shortened arms and legs (especially the upper arm and thigh)
  • Short stature (significantly below the average height for a person of the same age and sex)
  • Spinal stenosis
  • Spine curvatures called kyphosis and lordosis
• Signs and tests

  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.

• Treatment

  There is no specific treatment for achondroplasia. Related abnormalities, including spinal stenosis and spinal cord compression, should be treated when they cause problems.

• Expectations (prognosis)

  People with achondroplasia seldom reach 5 feet in height. Intelligence is in the normal range. Infants who receives the abnormal gene from both parents do not often live beyond a few months.

• Complications
  • Clubbed feet
  • Fluid build up in the brain (hydrocephalus)
• Calling your health care provider

  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.

• Prevention

  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.

• References

  Horton WA, Hecht JT. Disorders involving transmembrane receptors. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 694.

Review Date: 11/2/2009

Reviewed By: Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.