Achondroplastic Dwarfism: The Role of Genetics
Although achondroplastic dwarfism can be inherited, 80 percent of cases are due to new, sporadic mutations. These mutations involve the FGFR3 gene.
The FGFR3 gene makes a protein that regulates bone growth. It does this by limiting the formation of bone from cartilage (a process called ossification), particularly in the long bones of the arms and legs. Researchers believe that mutations in the FGFR3 gene cause the protein 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 "knock-out" mouse model in which the protein is absent. Without this protein, the 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.
Signs and Symptoms of Achondroplastic Dwarfism
All people with achondroplastic dwarfism have a short stature. The average height of an adult male with achondroplastic dwarfism is 131 centimeters (52 inches, or 4 feet 4 inches) and the average height for an adult female with achondroplastic dwarfism is 124 centimeters (49 inches, or 4 feet 1 inch).
The characteristic symptoms of achondroplastic 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.
People with achondroplastic dwarfism are generally of normal intelligence.
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