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Causes
By Mayo Clinic staff
It's estimated that Noonan syndrome occurs in one of 1,000 to 2,500 births. The cause is a mutation in a particular gene. Currently, scientists know of four genes that can cause Noonan syndrome. The mutation can be inherited from a parent who carries the defective gene (autosomal dominant), or it can develop because of a new mutation in children who don't have a genetic predisposition for the disease. Children who have one parent with Noonan syndrome have a 50 percent chance of developing the disorder.
The four known genes that may mutate and cause Noonan syndrome are:
- PTPN11 gene. About half the people with Noonan syndrome acquire the disorder because of a mutation of a gene called PTPN11.
- SOS1 gene. As many as 20 percent of people with Noonan syndrome have the condition because of a defect in this gene.
- RAF1 gene. This gene is responsible for up to 15 percent of all cases of Noonan syndrome.
- KRAS gene. About 5 to 10 percent of people acquire the disorder because of a mutation in the gene KRAS. People with this type of mutation may have a more severe form of Noonan syndrome.
Defects in these genes cause them to produce proteins that are continually active. Because these genes play a role in the formation of many tissues throughout the body, this constant activation of their proteins disrupts the normal process of cell growth and division.
In some people, none of these genes have a mutation, which may mean that some other, still undiscovered genes cause Noonan syndrome. In rare cases, people who have Noonan syndrome characteristics also have another condition called neurofibromatosis 1. People with these two conditions have a mutation in the neurofibromin 1 gene, which produces a protein that helps keep cells from growing too fast or in an uncontrolled way.
- Noonan syndrome. Genetics Home Reference. http://ghr.nlm.nih.gov/condition=noonansyndrome. Accessed Oct. 22, 2008.
- Learning about Noonan syndrome. National Human Genome Research Institute. http://www.genome.gov/25521674. Accessed Oct. 22, 2008.
- Allanson JE. Noonan syndrome. American Journal of Medical Genetics. 2007;145C: 274-279.
- Allanson JE. Noonan syndrome. GeneReviews. http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=noonan. Accessed Oct. 22, 2008.
- Lin AE. Adults with genetic syndromes and cardiovascular abnormalities: Clinical history and management. Genetics in Medicine. 2008;10(7):469-494.
- DeLuca A. NF1 gene mutations represent the major molecular event underlying neurofibromatosis-Noonan syndrome. The American Journal of Human Genetics. 2005;77(6):1092-1011.
- Tullu MS. Neurofibromatosis-Noonan syndrome or LEOPARD syndrome? A clinical dilemma. Journal of Postgraduate Medicine. 2000;46(2):98-100.
- Hoecker JL (expert opinion). Mayo Clinic, Rochester, Minn. Oct. 23, 2008.
