Cherubism

Cherubism is a rare genetic disorder that causes prominence in the lower portion in the face. The name is derived from the temporary chubby-cheeked resemblance to putti, often confused with cherubs, in Renaissance paintings.

Presentation
The appearance of people with the disorder is caused by a loss of bone in the mandible which the body replaces with excessive amounts of tissue. In most cases, the condition fades as the child grows, but in a few even rarer cases the condition continues to deform the afflicted person's face. Also causes premature loss of the primary teeth and uneruption of the permanent teeth.

Genetics
Mutations in the SH3BP2 gene have been identified in about 80 percent of people with cherubism. In most of the remaining cases, the genetic cause of the condition is unknown. The SH3BP2 gene provides instructions for making a protein whose exact function is unclear. The protein plays a role in transmitting chemical signals within cells, particularly cells involved in the replacement of old bone tissue with new bone (bone remodeling) and certain immune system cells.

Mutations in the SH3BP2 gene lead to the production of an overly active version of this protein. The effects of SH3BP2 mutations are still under study, but researchers believe that the abnormal protein disrupts critical signaling pathways in cells associated with the maintenance of bone tissue and in some immune system cells. The overactive protein likely causes inflammation in the jaw bones and triggers the production of osteoclasts, which are cells that break down bone tissue during bone remodeling. An excess of these bone-eating cells contributes to the destruction of bone in the upper and lower jaws. A combination of bone loss and inflammation likely underlies the cyst-like growths characteristic of cherubism.

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In some cases, an affected person inherits the mutation from one affected parent. Other cases may result from new mutations in the gene. These cases occur in people with no history of the disorder in their family.