Noonan syndrome (NS) is characterized by short stature, heart defect, and developmental delay of variable degree. Other findings can include broad or webbed neck, unusual chest shape with pectus carinatum or pectus excavatum, cryptorchidism, characteristic facies, varied coagulation defects, lymphatic dysplasias, and ocular abnormalities. Mutations in the PTPN11 gene are associated with Noonan syndrome and LEOPARD syndrome. Mutations in PTPN11 have been found in approximately 50% of patients with Noonan syndrome. Mutations specifically in exons 7, 12 and 13 of PTPN11 have been found in about 90% of patients with LEOPARD syndrome. Mutations in SOS1 have been found in approximately 10% of patients with Noonan syndrome. Mutations in RAF1 have been found in approximately 3.5-17% of patients with Noonan syndrome. Mutations in KRAS have been found in approximately 2-3% of patients with Noonan syndrome. This laboratory performs Sanger sequencing of the RAF1 gene.
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The majority of cases are due to sequence variants in PTPN11. Therefore, it is recommended to start with PTPN11 followed by SOS1, RAF1, and finally KRAS.
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