by Rick Alan
Achondroplasia is a genetic disorder that causes short stature called dwarfism and a large head, also known as macrocephaly. 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 reaching a full-grown height of less than four feet. The greatest shortening occurs in the bone between the shoulder and the elbow and the bone between the hip and the knee. There may also be underdevelopment of the face.
Achondroplasia is a genetic disorder. It is caused by mutations in the FGFR3 gene. This gene prevents the 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 children. In most cases of achondroplasia, it more commonly is the result of a sudden genetic defect that occurs in the developing embryo.
Those at risk of inheriting achondroplasia are:
Symptoms of achondroplasia include:
Other common symptoms include:
The doctor will ask about your symptoms and medical history. A physical exam will be done. The strength of your extremities and your bladder control will be evaluated. Weakness and loss of bladder are both signs of spinal stenosis, which is a narrowing of the spinal canal. It is important to follow the doctor's advice to make sure that spinal stenosis does not develop.
Your bodily fluids may be tested. This can be done with blood tests.
Images may be taken of your bodily structures. This can be done with:
Unfortunately, there is currently no treatment that can cure this condition. Scientists are exploring ways to create alternate growth factors which can bypass the missing receptor and lead to normal bone growth. They 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. It 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 adult height.
Surgery is sometimes needed to correct specific skeletal deformities.
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 demanding for both children and their families. Complications, sometimes serious, are common. One center has reported an average leg length 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.
There are no steps to prevent a genetic disorder. Genetic counseling can be used to discuss the chances that your child will have achondroplasia. You may consider this counseling if you are planning on having a child and have a family history of genetic conditions.
American Academy of Pediatrics
Little People of America
Canadian Paediatrics Society
Little People of Ontario
Achondroplasia. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed . Updated January 10, 2011. Accessed July 24, 2013.
Aldegheri R, Dall'Oca C. Limb lengthening in short stature patients. J Pediatr Orthop B . 2001 Jul;10(3):238-47.
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.
Last reviewed July 2013 by Kari Kassir, MD; Michael Woods, MD