Noonan syndrome is inherited in families in an autosomal dominant pattern. This means that the person with the condition has one copy of the altered gene which causes the disorder. The parent with Noonan syndrome has a 50% chance to pass on the altered gene to a child who will be affected. Alterations in four genes (PTPN11, SOS1, RAF1 and KRAS) have been identified so far. Noonan’s is present in about 1 in 1,000 to 1 in 2,500 people. Approximately 50% of individuals with this syndrome have mutations in the PTPN11 gene, 20% have mutations in the SOS1 gene, 10-15% have mutations in the RAF1 gene, and 5% have mutations in the KRAS gene which leads to a more severe or atypical form of the disorder. The cause of Noonan syndrome in the remaining 10-15% has yet to be identified.
There are many symptoms including: a characteristic facial structure/appearance, short stature, congenital heart defects, a broad or webbed neck, minor eye problems such as strabismus(abnormal alignment of the eyes), sunken or protruding chest, and sometimes mild cases of developmental delays. Approximately 50% of those with Noonan Syndrome will have the appearance of HCM. Others may have additional cardiac issues including the narrowing of the pulmonary valve which controls blood flow from the heart to the lungs.
Treatment is based on the individual’s particular symptoms. Cardiac issues are generally treated as they would be in others with similar cardiac manifestation. Early intervention programs can be utilized for those with developmental disabilities. In some with short stature, human growth hormones may be recommended however, extreme caution is advised as they may have an impact on the HCM heart.
Figure 1: Facial view of a 63 year old woman with Noonan syndrome.
Figure 2: Young girl with Noonan Syndrome
“Learning About Noonan Syndrome.” National Human Genome Research Institute (NHGRI), 23 Dec. 2013, www.genome.gov/25521674/learning-about-noonan-syndrome/.
“Noonan syndrome - Genetics Home Reference.” U.S. National Library of Medicine, National Institutes of Health, ghr.nlm.nih.gov/condition/noonan-syndrome.