Achondroplasia is a common cause of dwarfism. It occurs as a sporadic mutation in approximately 80% of cases (associated with advanced paternal age) or it may be inherited as an autosomal dominant genetic disorder.
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.
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
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 (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.
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