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 recessive 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.
Support & More Information
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Last Reviewed December 26, 2009