Genetics and Achondroplasia DwarfismAlthough achondroplasia dwarfism can be inherited, 80 percent of cases are due to new, sporadic mutations involving the FGFR3 gene.
The protein made by this gene is a receptor that regulates bone growth by limiting the formation of bone from cartilage (a process called ossification), particularly in the long bones. Researchers believe that mutations in the FGFR3 gene cause the receptor to be overly active, which interferes with ossification and leads to the disturbances in bone growth seen with this disorder.
This theory is supported by the knockout mouse model in which the receptor is absent. Therefore, the negative regulation of bone formation is lost. The result is a mouse with excessively long bones and elongated vertebrae, resulting in a long tail. Achondroplastic mouse models are useful tools in developing potential treatments.
(Click Achondroplasia Genetics for more information about the link between achondroplasia dwarfism and genetics.)
Signs and Symptoms of Achondroplasia Dwarfism
All people with achondroplasia dwarfism have a short stature. The average height of an adult male with the condition is 131 centimeters (52 inches, or 4 foot 4 inches), and the average height for an adult female with achondroplasia dwarfism is 124 centimeters (49 inches, or 4 foot 1 inch).
Characteristic symptoms of achondroplasia dwarfism include:
- An average-size trunk.
- Short arms and legs, with particularly short upper arms and thighs.
- An enlarged head (macrocephaly) with a prominent forehead.
- Fingers that are typically short. The ring finger and middle finger may diverge, giving the hand a three-pronged (trident) appearance.
(Click Symptoms of Achondroplasia for more information.)