What causes achondroplasia?
Achondroplasia is a genetic disease. This means that a gene that directs a specific process in the body does not work properly. In this particular condition, a protein in the body called the "Fibroblast Growth Factor Receptor" begins to function abnormally. The result is that the growth of bones, which normally occurs in the cartilage of the growth plate, is slowed. This leads to shorter bones, abnormally shaped bones, and shorter stature.
The genetic defect can be passed from a parent to his or her child. In the case of achondroplasia, however, it more commonly is the result of a spontaneous mutation (a sudden genetic defect) that occurs in the developing embryo.
What are the signs and symptoms of achondroplasia?
Patients with achondroplasia have a short stature, a long trunk, and shortened limbs which are noticeable at birth. Adults usually reach a height of between 42 and 56 inches. The head is large and the forehead is prominent. Portions of the face can be underdeveloped as well.
At birth, the legs appear straight, but as a child begins to walk, he or she develops a knock-knee or bowed -leg deformity. The hands and the feet appear large, but the fingers and toes are short and stubby. Straightening of the arm at the elbow may be restricted, but usually does not keep a patient with achondroplasia from doing any specific activities.
In addition, the child may develop an excessive curve of the lower back and a waddling walking pattern.
What are the different types of achondroplasia?
There are several recognized developmental disorders that mimic achondroplasia. First, in a condition called pseudo-achondroplasia, the face of the child appears normal, but he or she may have irregular growth plates in the hips and knees. In another condition called hypochondroplasia, the child is less severely affected. He or she usually develops a height over 54 inches and does not ever get spinal stenosis (see below).
What is the treatment of achondroplasia?
Unfortunately, there is no treatment that can cure this condition. Surgery is sometimes needed to correct specific skeletal deformities. For example, in patients with severe knock-knee or bowed legs, the pediatric orthopaedic surgeon can perform an osteotomy in which he or she cuts the bones of the leg and allows them to heal in a more correct anatomical position. For significant spinal kyphosis (see Patient Guide to Kyphosis) a spinal fusion sometimes is performed (permanently connecting otherwise separate vertebrae).
The most serious complication of achondroplasia is the narrowing of the spinal canal called "spinal stenosis." The canal houses the spinal cord and such narrowing can lead to a compression of the cord and severe neurological problems. Surgical decompression of the cord is needed to relieve the pressure on it. This is done by opening the canal at the affected levels in a procedure called a "laminectomy."
Should my child see a doctor regularly?
Yes. It is important to follow a doctor to make sure that spinal stenosis does not develop. The physician evaluates the strength of the extremities and bladder control. Weakness and loss of bladder control are both signs of developing spinal stenosis.
How will a child do in the long run with achondroplasia?
The prognosis depends on the severity of the disease. Patients who have two copies of the deficient gene (i.e. one from each parent, also known as "homozygous") generally die a few weeks to months after birth. Those with one copy (i.e. from only one parent, also known as "heterozygous") have a normal life span and intelligence. They are usually independent in their daily life activities. Many of these patients, in fact, have gone on to do great things in life.
Colleen Cullen, CRNP
Kristen Venuti, CRNP
Peggy Wilckens, MMS, PA-C
Mary Teresa (Tresie) Yost, FNP-C
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