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Achondroplasia

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 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.

Review Date 11/19/2015

Updated by: Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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