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Achondroplasia

Achondroplasia is a growth disorder caused by a specific genetic mutation. As a result, cartilage has difficulty converting to bone, which usually results in dwarfism. Although there is no cure for achondroplasia, treatments are available to help relieve symptoms and health conditions (such as breathing problems) that are often associated with this disorder.

 

What Is Achondroplasia?

Achondroplasia is one of the most common causes of dwarfism. Characteristics of a person with the disease include:
 
  • A short stature with proportionately short arms and legs
  • A large head
  • A prominent forehead
  • A flattened bridge of the nose.
 
Achondroplasia is a bone growth disorder. Although the word literally means "without cartilage formation," the problem is not the formation of cartilage. The problem occurs when the cartilage has difficulty converting to bone, especially in the long bones of the arms and legs.
 

Signs and Symptoms of Achondroplasia

All people with achondroplasia 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 is 124 centimeters (49 inches, or 4 foot 1 inch).
 
Characteristic symptoms 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.)
 

Health Problems Associated With Achondroplasia

Health problems commonly associated with this disorder include:
 
  • Breathing disorders (apnea)
  • Reduced muscle strength
  • Obesity
  • Recurrent ear infections
  • Crowded teeth.
     
Adults with achondroplasia usually develop a pronounced and permanent sway of the lower back (lordosis) and bowed legs. It can also cause back pain in older individuals, which can cause difficulty with walking.
 

Treatment for Achondroplasia

There is no cure for achondroplasia. However, treatment options can treat the signs, symptoms, and health conditions that occur as a result of the disease.
 
(Click Achondroplasia Treatments for more information.)
 

How Common Is Achondroplasia?

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

Prognosis With Achondroplasia

The prognosis of people with achondroplasia depends on the severity of their condition. In 2 to 5 percent of all cases, newborns do not survive more than 12 months after birth. These cases are considered a severe form of the disease. However, most people with achondroplasia should expect to live a normal lifespan and have normal intelligence.
 

Cause of Achondroplasia

Most people with the disorder have average-size parents, which means that achondroplasia is caused by a new mutation in the fibroblast growth factor receptor 3 (FGFR3) gene. Scientists do not know why this mutation occurs.
 
(Click FGFR3 Gene for more information.)
 
Achondroplasia can also be inherited in an autosomal dominant pattern, which means that one copy of the altered gene in each cell is sufficient to cause the disorder. In these cases, one of the parents with achondroplasia passes the FGFR3 gene to the child.
 
If one parent has achondroplasia, children have a 50 percent chance of inheriting the FGFR3 gene. If both parents have it, children have a one in four chance of inheriting the gene from both parents. Newborns who inherit both genes are considered to have a severe form of achondroplasia, where survival is usually less than 12 months after birth.
 
(Click Cause of Achondroplasia for more information.)
 

Genetics and Achondroplasia

Although achondroplasia can be inherited, 80 percent of cases are due to new, sporadic mutations involving the FGFR3 gene. The protein made by the 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 FGFR3 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.)
 

Other Names for Achondroplasia

Other names for this condition include:
 
  • ACH
  • Achondroplastic dwarfism
  • Chondrodystrophia fetalis
  • Chondrodystrophy syndrome
  • Congenital osteosclerosis
  • Dwarf, achondroplastic
  • Osteosclerosis congenital.
     
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Written by/reviewed by: Arthur Schoenstadt, MD
Last reviewed by: Arthur Schoenstadt, MD