Achondroplasia

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at August 25, 2016
StartDiseasesAchondroplasia

Achondroplasia is the most common form of dwarfism, and it involves the arms and legs being shorter than normal while the torso remains an average size. The condition can cause several other minor health problems or risks, but people with achondroplasia usually have a normal life expectancy. With some treatments and lifestyle choices, they can manage their symptoms and reduce their risk for other illnesses.

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Definition & Facts

Achondroplasia is a type of dwarfism in which the body struggles with ossification, or converting cartilage into bone. During early development, a large portion of the skeleton is made up of cartilage, which is a flexible tissue. Over time, the cartilage should convert into bone.

The word achondroplasia means "without cartilage formation," and the condition especially causes trouble with ossification in the arms and legs. People with the condition tend to have a short stature, short arms and legs, and an average-sized torso.

Achondroplasia affects 1 in 15,000 to 40,000 people. The average height of a male with the condition is 4 feet and 4 inches, and the average height of a female is 4 feet and 1 inch.

Symptoms & Complaints

A short stature and short limbs are the most common and visible effects of achondroplasia. People with the condition also often have short fingers and trident hands, a large head, and a flattened nasal bridge.

Achondroplasia can cause spinal kyphosis, which is an outward curvature of the spine, or lordosis, which is an inward curvature of the spine. Infants with the condition often have hypotonia, or weak muscle tone, which can cause a delay in the development of gross motor skills like walking.

In some rare situations, children with achondroplasia can be born with hydrocephalus, or the buildup of fluid in the brain. The condition is usually accompanied by other health complications, including sleep apnea, where a person's breathing stops for short time periods.

People with achondroplasia also tend to get ear infections more frequently than people without the condition. On rare occasions, achondroplasia can cause spinal stenosis, the narrowing of the spinal canal that results in compressing the spinal cord. This can cause pain, weakness in the legs, and difficulty walking.

Causes

Achondroplasia is caused by a genetic mutation in the fibroblast growth factor receptor, or FGFR3 gene. This gene is responsible for creating a protein that helps develop bone tissue and brain tissue, and the genetic mutation leads to shortened bones.

Achondroplasia is inherited in an autosomal dominant pattern, meaning that one copy of the genetic mutation can cause the disorder. If the child receives the genetic mutation from both parents, it is called homozygous achondroplasia. In this situation, the child usually dies before or shortly after birth.

Although the condition can be passed on from parent to child, about 80 percent of people with the condition are born to parents without dwarfism. This can happen as a result of a new mutation in the gene.

Children with a father older than 35 are more likely to be born with the condition. Parents of normal height who have one child with achondroplasia are very unlikely to have another child with the condition.

Diagnosis & Tests

Achondroplasia can often be diagnosed before birth by using a prenatal ultrasound. If the baby shows signs of the condition during an ultrasound, doctors can perform a DNA test before the baby is born by testing a sample of amniotic fluid for the mutated FGFR3 gene. They can also use genetic testing to determine whether the baby will be born with homozygous achondroplasia, which is fatal.

After a baby is born, doctors can consider many factors to determine whether they have achondroplasia. Doctors can look for a short stature, shortened arms and legs, a limited ability to extend the elbow, bow legs, or curvature of the spine.

They also may use a skeletal survey to diagnose the condition. During this test, doctors observe the size and shape of the skull, the vertebrae, the ribs, and the bones in the hands, arms, and legs. Genetic testing after birth (newborn screening) is accurate in about 99 percent of individuals with the condition.

Treatment & Therapy

There isn't a cure of achondroplasia, but people with the condition can undergo treatments to relieve or fix complications. Doctors have tried using growth hormone therapy, but it is not effective as a long-term treatment. People with the condition should visit a doctor regularly for checkups in order to prevent common complications like sleep apnea and ear infections.

Some surgical treatments are available that help with some of the symptoms of achondroplasia. These surgeries can correct the direction of bone growth and correct the shape of the spine. If a baby is born with hydrocephalus, doctors can perform a surgery to remove the excess fluid from the brain.

People with achondroplasia also sometimes to decide to have a limb lengthening surgery, but this is a controversial procedure. There are many risks to the surgery, and it usually takes multiple procedures to complete the treatment.

Many small lifestyle changes and home remedies can ease the symptoms or complications of the condition as well. Children with the condition should always use car seats that have firm support of the back and neck, and they should avoid carriers or play equipment like strollers or swings that cause the back to be curved into a C shape. Many people with achondroplasia struggle with weight gain, so a healthy diet and activities like swimming and bicycling can prevent obesity.

Prevention & Prophylaxis

Although doctors can diagnose achondroplasia before birth, there is no way to prevent the condition. People with the condition who are considering having children can see a genetic counselor to talk about the chances of their child having the condition as well.

Doctors advise that people with achondroplasia carefully consider the health risks associated with the condition before deciding to have children, especially if their partner has the condition as well.