What is achondroplasia?

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).

People with achondroplasia have normal intelligence and a normal lifespan.

What causes achondroplasia?

Achondroplasia is caused by an alteration in the FGFR3 gene, which results in abnormal cartilage and bone formation. Males and females are equally affected. Most cases of achondroplasia result from a new (de novo) mutation in the child, where the parents are of average height and do not have the abnormal gene. Where inheritance is involved, it is an autosomal dominant condition, which means that only one abnormal gene, inherited from one parent, is necessary to have the condition.

What are the symptoms of achondroplasia?

Each child may have different symptoms. Common symptoms may include:

• Shortened thighs and upper arms
• Bowed lower legs
• Short fingers, with extra space between the middle and ring fingers
• Short feet
• Large head size with a prominent forehead
• Flat nose with depressed nasal bridge
• Curved lower spine (lordosis), which may lead to the development of a small hump near the shoulders (kyphosis) that usually goes away after the child begins walking
• Poor muscle tone
• Loose joints
• Difficulty straightening the elbows
• Short spells of slow or stopped breathing, especially during sleep (obstructive sleep apnea)
• Frequent ear infections that may lead to hearing loss
• Delayed developmental milestones, such as sitting, crawling or walking
• Short stature as the child grows (but typically normal length at birth)
• Crowded teeth

The symptoms of achondroplasia may look like other problems or medical conditions. Always consult your child's doctor for a diagnosis.

Potential complications and risks

The interrupted breathing (obstructed sleep apnea) associated with achondroplasia can increase the risk of sudden infant death syndrome (SIDS). Occasionally, a child with achondroplasia may die suddenly in infancy or early childhood during sleep due to compression of the upper end of the spinal cord, which interferes with breathing.

How is achondroplasia diagnosed?

Achondroplasia can be diagnosed before birth by fetal ultrasound or after birth by complete medical history and physical exam. X-ray imaging may be used to detect abnormal bone development. A computed tomography (CT) scan or magnetic resonance imaging (MRI) may be used to detect spinal cord compression or evaluate severe muscle weakness.

DNA testing is available before birth to confirm fetal ultrasound findings for parents who are at increased risk for having a child with achondroplasia.

How is achondroplasia treated?

Currently, there is no way to prevent achondroplasia, since most cases result from unexpected new mutations. Treatment addresses symptoms or results of the condition that can affect health and well-being.

• Vosoritide was the first medication approved by the FDA for the treatment of achondroplasia. It is a c-natriuretic peptide (CNP) analog that works at the growth plates of the long bones to promote growth by reducing FGFR3 activity. Clinical studies have shown that children with achondroplasia treated with vosoritide grow an average of 1.5 cm more per year compared to no treatment. It can only be used until the growth plates closed. A number of other medications to promote growth in achondroplasia are currently being studied and may be available in the future.
• Leg-lengthening surgeries may be considered in specific cases.
• Detecting bone abnormalities, particularly in the back, is important to prevent breathing difficulties, leg pain and/or loss of significant function.
• Kyphosis (or hunchback) may need to be surgically corrected if it does not disappear when the child begins walking.
• Surgery may help correct bowing of the legs.
• Pressure on the brain (intracranial pressure) may need to be treated with surgery.
• Breathing interruptions during sleep (obstructive sleep apnea) may be treated with weight reduction, positive airway pressure or surgery to remove the adenoids and tonsils.
• Ear infections need to be treated immediately to avoid the risk of hearing loss.
• Dental problems may need to be addressed by an orthodontist.

Lifestyle changes to address obesity may be part of a child’s treatment. Children with achondroplasia are prone to obesity, and obesity can contribute to back pain and obstructive sleep apnea.

Treatment with growth hormone does not substantially affect the height of a person with achondroplasia.

Follow-up care

Because achondroplasia can affect different body functions, ongoing coordinated care by a team of appropriate specialists may be needed.

Medical treatment of achondroplasia at Children’s Hospital of Philadelphia (CHOP) is managed by the Center for Bone Health, which provides comprehensive, coordinated care in collaboration with other specialty departments.

Depending on the patient’s diagnosis and condition, coordinated care might include specialists in:

• Endocrinology / Bone Health
• Orthopedics
• Neurology
• Pain management
• Physical and occupational therapy
• Nutrition
• Genetics