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Achondroplasia

  • Definition
    • Achondroplasia is a disorder of bone growth that causes the most common type of dwarfism.

  • Causes
    • 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 1 parent, the child will have the disorder. If 1 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 2 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)
      • Narrowing of the spinal column spinal stenosis
      • Spine curvatures called kyphosis and lordosis
  • Exams 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.

  • Outlook (Prognosis)
    • People with achondroplasia seldom reach 5 feet (1.5 meters) 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.

  • Possible Complications
    • Health problems that may develop include:

      • Breathing problems from a small upper airway and from pressure on the area of the brain that controls breathing
      • Lung problems from a small ribcage
  • When to Contact a Medical Professional
    • 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 1 or both have achondroplasia. However, because achondroplasia most often develops spontaneously, prevention is not always possible.

  • References
    • Carson BS, Groves M, Yassari R. Neurologic problems of the spine in achondroplasia. In: Quiñones-Hinojosa A, ed. Schmidek and Sweet's Operative Neurosurgical Techniques. 6th ed. Philadelphia, PA: Elsevier Saunders; 2012:chap 184.

      Horton WA, Hecht JT. Disorders involving transmembrane receptors. In: Kliegman RM, Stanton BF, St. Geme JW III, Schor NF, eds. Nelson Textbook of Pediatrics. 20th ed. Philadelphia, PA: Elsevier; 2016:chap 696.