Alternative Names
ACH; Achondroplastic dwarfism; Chondrodystrophia fetalis; Chondrodystrophy syndrome; Congenital osteosclerosis; Dwarf, achondroplastic; Osteosclerosis congenita
Symptoms & Characteristics
Achondroplasia is a genetic condition that affects bone growth. Although achondroplasia literally means "without cartilage formation," the problem is not in forming cartilage but in converting it to bone, particularly in the long bones of the arms and legs.
All people with achondroplasia have short stature. The average height of an adult male with achondroplasia is 131 centimeters (4 feet, 4 inches), and the average height for adult females is 124 centimeters (4 feet, 1 inch).
Characteristic features of achondroplasia include an average-size trunk, short arms and legs with particularly short upper arms and thighs, limited range of motion at the elbows, and an enlarged head (macrocephaly) with a prominent forehead. Fingers are typically short and the ring finger and middle finger may diverge, giving the hand a three-pronged (trident) appearance. People with achondroplasia are generally of normal intelligence.
Health problems commonly associated with achondroplasia include episodes in which breathing slows or stops for short periods (apnea), obesity, and recurrent ear infections. In adulthood, people with this disorder usually develop a pronounced and permanent sway of the lower back (lordosis) and bowed legs. Older individuals often have back pain, which can cause difficulty with walking.
Management & Treatment
Early diagnosis, routine surveillance and treatment of achondroplasia may help to manage some of the symptoms and sometimes prevent related problems. Treatment is primarily aimed at addressing skeletal issues and sleep apnea.
How Common Is It?
Achondroplasia is the most common type of short-limbed dwarfism and affects about 1 in 15,000 to 40,000 newborns.
Genetics & Inheritance
Achondroplasia is caused by mutations in the FGFR3 gene on chromosome 4 at the location p16.3.
- The FGFR3 gene provides instructions for making a protein that is involved in the development and maintenance of bone and brain tissue. This protein limits the formation of bone from cartilage (a process called ossification), particularly in the long bones.
- Two specific mutations in the FGFR3 gene are responsible for about 99% of cases of achondroplasia. The remaining 1% are caused by different mutations in the same gene. Researchers believe that these mutations cause the protein to be overly active, which interferes with skeletal development and leads to the disturbances in bone growth seen with this disorder.
Achondroplasia is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. An affected person has a 50% chance with each pregnancy to have an affected child.
About 80% of people with achondroplasia have average-size parents; these cases result from a new mutation in the FGFR3 gene. In the remaining cases, people with achondroplasia have inherited an altered FGFR3 gene from one or two affected parents. Individuals who inherit two altered copies of this gene typically have very severe problems with bone growth, and are usually stillborn or die shortly after birth from respiratory failure.
Genetic Testing
Clinical genetic testing for achondroplasia may be available through genetic consultation for people who are considered at risk. A trained genetic professional can discuss the benefits and limitations of genetic testing, any management and treatment options, as well as assess the odds of having a child with this condition.
- A board-certified genetic counselor is available by telephone.
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