Achondroplasia is an inherited disorder of bone growth. It is one of the group of disorders that are collectively called chondrodystrophies or osteochondrodysplasias.

The disorder causes a type of dwarfism that is recognized by its characteristic normal to large-sized head, shortened arms and legs (especially the upper arm and thigh), a normal-sized trunk, and waddling gait. Achondroplasia is the most common type of dwarfism.

Achondroplasia is inherited as an autosomal dominant trait. However, the majority of cases, approximately 80%, appear as spontaneous mutations. 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%.

• short stature
• short limbs, proximal extremity (upper arm and thigh)
• large appearing head
• skeletal (limb) abnormalities
• Abnormal hand appearance (trident hand) with persistent space between the long and ring fingers
• marked kyphosis and lordosis (spine curvatures)
• waddling gait
• prominent (conspicuous) forehead (frontal bossing)
• increased inward curve of lower back making the buttocks appear more prominent (lordosis)
• increased outward curve of upper back making back appear slightly hunched (kyphosis)
• head appears disproportionately large for body
• hypotonia
• polyhydramnios (present when affected infant is born)
• bowed legs

Notes: A family history of achondroplasia should alert parents to the possibility of having an affected child. Typical appearance of achondroplastic dwarfism is apparent at birth.

Examination of the infant shows increased front-to-back head size (occipital-frontal circumference). There may be signs of hydrocephalus associated with enlargement of the chambers within the center of the brain (ventricular dilatation).

Tests that identify achondroplasia include:
X-rays of the long bones (see bone X-ray) can demonstrate achondroplasia in the newborn.

People with achondroplasia seldom reach five feet in height. Mentality is normal. Infants who are homozygous for achondroplasia (both parents are achondroplastic and each has contributed an affected gene) seldom live beyond a few months.

• hydrocephalus
• club feet

Call for an appointment with your health care provider if you are planning to have children and there is a family history of achondroplasia.

Genetic counseling may be helpful for prospective parents when one or both have achondroplasia. Because achondroplasia arises as a spontaneous mutation, absolute prevention is not possible.