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 )

  Frontal bossing

  Frontal bossing is an unusually prominent forehead. It is sometimes associated with a heavier than normal brow ridge.

   

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• 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

  Spinal stenosis

  Spinal stenosis is narrowing of the spinal column that causes pressure on the spinal cord, or narrowing of the openings (called neural foramina) wher...

   

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• Spine curvatures called kyphosis and lordosis

  Kyphosis

  Kyphosis is a curving of the spine that causes a bowing or rounding of the back. This leads to a hunchback or slouching posture.

   

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  Lordosis

  Lordosis is the inward curve of the lumbar spine (just above the buttocks). A small degree of lordosis is normal. Too much curving is called swayba...

   

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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.