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 26,000 to one in 40,000 live births.
Achondroplasia is a genetic disorder. It is caused by mutations in the FGFR3 gene that inhibits growth of cartilage at the growth plate. FGFR3 encodes a protein called Fibroblast Growth Factor Receptor 3. This protein is the site of action of a major growth factor responsible for lengthening bones. When this growth factor cannot act properly due to the absence of its receptor, the growth of bones, at the growth plate's cartilage, 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 to offspring. 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.
A risk factor is something that increases your chances of getting a disease or condition. Those at risk of inheriting achondroplasia are:
Patients with achondroplasia have:
Other common symptoms include:
The prognosis depends on the severity of the disease. Patients who have two copies of the deficient gene (ie, one from each parent, also known as homozygous) generally die a few weeks to months after birth. Those with one copy (ie, from only one parent, also known as heterozygous) have a normal life span and intelligence, although children often take longer to develop normal motor skills and there is an increased risk of death in the first year of life due to respiratory problems. They are usually independent in their daily life activities. Many of these patients, in fact, have gone on to do great things in life.
Diagnosis includes:
Unfortunately, there is currently no treatment that can cure this condition. Because we now know that achondroplasia is caused by an absence of growth factor receptor, scientists are exploring ways to create alternate growth factors which can bypass the missing receptor and lead to normal bone growth. Such treatments are still well in the future but may offer the possibility of enhanced stature to future families who have children with achondroplasia.
Treatment with human growth hormone has been used for over a decade and effectively increases bone growth rate, at least in the first year of life. There have been few studies looking at whether children treated with growth hormone achieve greater (or normal) adult heights.
Surgery is sometimes needed to correct specific skeletal deformities.
While osteotomy has primarily been used to correct deformities, in recent years bone lengthening procedures have been used for many short children, including those with achondroplasia. The procedures are lengthy, traumatic, and very demanding for both children and their families. Complications, sometimes serious, are common. One center has reported an average leg length (height) gain of about seven inches and an average increase in arm length of about four inches for achondroplastic individuals who undergo surgery. The combination of growth hormone therapy followed by lengthening surgery may provide benefit in achieving near-normal stature and proportions.
RESOURCES:
American Academy of Pediatrics
http://www.aap.org
Little People of America
http://www.lpaonline.org
March of Dimes
http://www.modimes.org
CANADIAN RESOURCES:
Little People of Ontario
http://www.lpo.on.ca/
References:
Aldegheri R, Dall'Oca C. Limb lengthening in short stature patients. J Pediatr Orthop B . 2001 Jul;10(3):238-47.
American Academy of Pediatrics website. Available at: http://www.aap.org .
Aviezer D, Golembo M, Yayon A. Fibroblast growth factor receptor-3 as a therapeutic target for achondroplasia--genetic short limbed dwarfism. Curr Drug Targets . 2003;4(5):353-65.
Berkow R. The Merck Manual of Medical Information . New York, NY: Simon and Schuster, Inc.; 2000.
Cotran RS, Kumar V, Collins T, Robbins, SL. Robbins Pathologic Basis of Disease . Philadelphia, PA: WB Saunders Co; 1999.
National Library of Medicine website. Available at: http://www.nlm.nih.gov/ . Published October 1993. Updated May 2009.
Last reviewed November 2008 by Rosalyn Carson-DeWitt, MD
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