Definition
Achondroplasia is a genetic disorder that causes dwarfism (short stature). It is a disorder in which bone and cartilage do not grow normally. It is the most common cause of dwarfism.
This condition leads to patients attaining a full-grown height of less than four feet. The greatest shortening occurs in the humerus (the bone between the shoulder and the elbow) and the femur (the bone between the hip and the knee). There may also be underdevelopment of the face.
Achondroplasia is the most common form of inherited disproportionate short stature. It occurs in one in 15,000 to one in 40,000 live births.
Causes
Achondroplasia is a genetic disorder. It is caused by mutations in the FGFR3 gene that inhibits growth of cartilage at the growth plate. 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 gene for achondroplasia can be passed from one generation to the next. If a parent has the disorder there is a 50% chance of passing the gene for achondroplasia on to offspring (Autosomal Dominant Inheritance). In most cases of achondroplasia (80-90%), it more commonly is the result of a spontaneous mutation (a sudden genetic defect) that occurs in the developing embryo.
Risk Factors
A risk factor is something that increases your chances of getting a disease or condition. Those at risk of inheriting achondroplasia are:
• Children of a parent with achondroplasia
• Children of normal-sized parents who carry a mutated FGFR3 gene
• Advanced paternal age causing spontaneous mutations
Symptoms
Patients with achondroplasia have:
• 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
• 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
• Children may develop an excessive curve of the lower back and a waddling walking pattern
Other common symptoms include:
• Weight control problems
• Bowed legs
• Middle ear infections, especially in children
- If not treated properly, can result in hearing loss
• Dental problems (from overcrowding of teeth)
• Hydrocephalus (water on the brain)
• Neurologic and respiratory problems
• Spinal compression
• Fatigue, pain, and numbness in the:
- Lower back
- Spine
People with achondroplasia are generally of normal intelligence. Other than short stature, their overall development is usually normal. However, children often take longer to develop normal motor skills.
Diagnosis
Diagnosis includes:
• Clinical Evaluation
• Radiographs
• Molecular genetic testing can be used to detect a mutation in the FGFR3 gene (chromosomal locus 4p16.3). Such testing is 99% sensitive and is available in clinical laboratories. A doctor can usually diagnose the disorder in a newborn from observation of physical symptoms. To confirm that dwarfism is caused by achondroplasia, x-rays are taken.
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.
Treatment
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 orthopedic 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, 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."
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.
