Article: Achondrogenesis, type 2

Achondrogenesis, type 2 is a severe, inherited disorder of bone growth. The disorder is characterized by a short body and limbs and a lack of bone formation in the spine and pelvis. Achondrogenesis, type 2 is a subtype of collagenopathy, types II and XI.

Infants with this disorder have short arms and legs, a small chest with short ribs, and underdeveloped lungs. The skull bones may be soft, but they often appear normal on X-ray images. In contrast, bones in the spine (vertebrae) and pelvis do not harden. Typical facial features include a prominent forehead, a small chin, and, in some cases, an opening in the roof of the mouth (a cleft palate). The abdomen is enlarged, and excess fluid builds up in the body before birth (a condition called hydrops fetalis).

As a result of these serious health problems, infants are usually premature and stillborn or die shortly after birth from respiratory failure. Some infants have lived for a time, however, with intensive medical support.

Achondrogenesis, type 2 is the most severe condition in a spectrum of disorders caused by mutations in the COL2A1 gene. The protein made by this gene forms type II collagen, a molecule found mostly in cartilage and in the clear gel that fills the eyeball (the vitreous). Type II collagen is essential for the normal development of bones and other connective tissues. Mutations in the COL2A1 gene interfere with the assembly of type II collagen molecules, which prevents bones from developing properly.

This condition is almost always caused by new mutations in the COL2A1 gene. Achondrogenesis, type 2 is considered an autosomal dominant disorder because one copy of the altered gene is sufficient to cause the condition. The disorder is not passed on to the next generation, however, because affected individuals hardly survive past puberty.

This article incorporates public domain text from The U.S. National Library of Medicine