Costello Syndrome - Genetics

Genetics

Costello syndrome is caused by any of at least five different mutations in the HRAS gene on chromosome 11. This gene provides instructions for making a protein, H-Ras, that helps control cell growth and division. Mutations that cause Costello syndrome lead to the production of an H-Ras protein that is permanently active. Instead of triggering cell growth in response to particular signals from outside the cell, the overactive protein directs cells to grow and divide constantly. This unchecked cell division may predispose sufferers to the development of benign and malignant tumors. It remains unclear how mutations in HRAS cause other features of Costello syndrome, but many of the signs and symptoms may result from cell overgrowth and abnormal cell division.

HRAS is a proto-oncogene in which somatic mutations in healthy people can contribute to cancer. Whereas children with Costello syndrome typically have a mutation in HRAS in every cell of their bodies, an otherwise healthy person with a tumor caused in part by HRAS mutation will only have mutant HRAS within the tumor. The test for the mutation in cancer tumors can also be used to test children for Costello syndrome.

Costello syndrome is inherited in an autosomal dominant manner, which means one copy of the altered gene is sufficient to cause the disorder. Almost all cases have resulted from new mutations, and occur in people with no history of the disorder in their family. This condition is rare; as of 20 April 2007, 200 to 300 cases have been reported worldwide.