A.D.A.M. Medical Encyclopedia.
Last reviewed: November 13, 2011.
Achondroplasia is a disorder of bone growth that causes the most common type of dwarfism.
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.
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.
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.
“There’s been a lot of discussion over the years about the proper way to refer to someone with dwarfism. Many people who have the condition prefer the term “little person” or “person of short stature.” For some, “dwarf” is acceptable. For most, “midget” definitely is not.
But here’s an idea everyone can agree on: Why not simply call a person with dwarfism by his or her name?
Being of short stature is only one of the characteristics that make a little person who he or she is. If you’re the parent or loved one of a little person, you know this to be true.”