Achondroplasia is a group of rare genetic (inherited) bone disorders. Achondroplasia is the most common type of what was once called dwarfism, in which the child's arms and legs are short in proportion to body length. The head is often large and the trunk is normal size. The average height of adult males with achondroplasia is about 52 inches (or 4 feet, 4 inches). The average height of adult females with achondroplasia is about 49 inches (or 4 feet, 1 inch).
Achondroplasia is a genetic disease that causes abnormal cartilage formation. Males and females are equally affected. It is an autosomal dominant disease, which means that only one abnormal gene inherited from one parent is necessary to have the condition. Most cases of achondroplasia result from a new mutation in families in which the parents are average height and do not have the abnormal gene.
Each child may have different symptoms. Common symptoms may include:
- Short arms, legs, and fingers
- Upper arms and thighs more shortened than the forearms and lower legs
- Large head size with prominent forehead and a flattened nasal bridge
- Crowded or misaligned teeth
- Curved lower spine (lordosis or "sway-back") which may lead to kyphosis (hunchbacK), the development of a small hump near the shoulders that usually goes away after the child begins walking.
- Small vertebral canals (spine or back bones) which may lead to spinal cord compression in adolescence. Occasionally a child with achondroplasia may die suddenly in infancy or early childhood in during sleep due to compression of the upper end of the spinal cord, which interferes with breathing.
- Bowed lower legs
- Flat feet that are short and broad
- Extra space between the middle and ring fingers (also called a trident hand.)
- Poor muscle tone and loose joints
- Short spells of slow or stopped breathing (called apnea)
- Frequent middle ear infections which may lead to hearing loss
- Delayed developmental milestones, such as walking (which may occur between 18 to 24 months instead of around one year of age)
People with achondroplasia have normal intelligence and normal lifespan.
The symptoms of achondroplasia may look like other problems or medical conditions. Always consult your child's doctor for a diagnosis.
Achondroplasia can be diagnosed before birth by fetal ultrasound or after birth by complete medical history and physical exam. DNA testing is now available before birth to confirm fetal ultrasound findings for parents who are at increased risk for having a child with achondroplasia.
Currently, there is no way to prevent or treat achondroplasia, since most cases result from unexpected new mutations. Treatment with growth hormone does not substantially affect the height of an person with achondroplasia. Leg-lengthening surgeries may be considered in specific cases.
Detection of bone abnormalities, particularly in the back, is important to prevent breathing difficulties, leg pain, and or loss of significant function. Kyphosis (or hunch-back) may need to be surgically corrected if it does not disappear when the child begins walking. Surgery may also help bowing of the legs. Ear infections need to be treated immediately to avoid the risk of hearing loss. Dental problems may need to be addressed by an orthodontist (a dentist with special training in the alignment of teeth).
Research into the family of genes called fibroblast growth factors discovered the gene that causes achondroplasia. The goal is to understand how the faulty gene causes the features seen in achondroplasia, in order to lead to improved treatment. These genes have been linked to many other heritable skeletal disorders.