Achondroplasia

What is achondroplasia?

Achondroplasia is a disorder of bone growth. Although achondroplasia literally means "without cartilage formation," in this disorder 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 (52 inches, or 4 foot 4 inches), and the average height for adult females is 124 centimeters (49 inches, or 4 foot 1 inch). Characteristic features of achondroplasia include an average-size trunk, short arms and legs with particularly short upper arms and thighs, 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 breathing disorders (apnoea), obesity, and recurrent ear infections. Adults with the condition 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.

How common is achondroplasia?

Achondroplasia is the most common type of short-limbed dwarfism. The condition affects 1 in 15,000 to 40,000 births.

What genes are related to achondroplasia?

Mutations in the FGFR3 gene cause achondroplasia.

The protein made by the FGFR3 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.

How do people inherit achondroplasia?

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. Most people with achondroplasia have average-size parents; these cases result from a new mutation in the FGFR3 gene. Other people with achondroplasia inherited an altered FGFR3 gene from a parent who has the condition.

What other names do people use for achondroplasia?

* ACH
* Achondroplastic dwarfism
* Chondrodystrophia foetalis
* Chondrodystrophy syndrome
* Congenital osteosclerosis
* Dwarf, achondroplastic
* Osteosclerosis congenita