Question: What are the genetic changes related to Costello syndrome ?
Answer: Mutations in the HRAS gene cause Costello syndrome. This gene provides instructions for making a protein called H-Ras, which is part of a pathway that helps control cell growth and division. Mutations that cause Costello syndrome lead to the production of an H-Ras protein that is abnormally turned on (active). The overactive protein directs cells to grow and divide constantly, which can lead to the development of cancerous and noncancerous tumors. It is unclear how mutations in the HRAS gene cause the other features of Costello syndrome, but many of the signs and symptoms probably result from cell overgrowth and abnormal cell division. Some people with signs and symptoms of Costello syndrome do not have an identified mutation in the HRAS gene. These individuals may actually have CFC syndrome or Noonan syndrome, which are caused by mutations in related genes. The proteins produced from these genes interact with one another and with the H-Ras protein as part of the same cell growth and division pathway. These interactions help explain why mutations in different genes can cause conditions with overlapping signs and symptoms.
Source: GHR

Question: Is Costello syndrome inherited ?
Answer: Costello syndrome is considered to be an autosomal dominant condition, which means one copy of the altered gene in each cell is sufficient to cause the disorder. Almost all reported cases have resulted from new gene mutations and have occurred in people with no history of the disorder in their family.
Source: GHR