Noonan syndrome (NS) is an autosomal dominant disorder caused by mutations in PTPN11, KRAS, SOS1, and RAF1. We performed SOS1, RAF1, BRAF, MEK1, and MEK2 mutation analysis in a cohort of 102 PTPN11- and KRAS-negative NS patients and found pathogenic SOS1 mutations in 10, RAF1 mutations in 4, and BRAF mutations in 2 patients. Three novel SOS1 mutations were found. One was classified as a rare benign variant and the other remains unclassified. We confirm a high prevalence of pulmonic stenosis and ectodermal abnormalities in SOS1-positive patients. Three patients with SOS1 mutations presented with tumors (embryonal rhabdomyosarcoma, Sertoli cell testis tumor, and granular cell tumors of the skin). One patient with a RAF1 mutation had a lesion suggestive for a giant cell tumor. This is the first report describing different tumor types in NS patients with germ line SOS1 mutations.

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The diagnosis of Noonan syndrome is essentially clinical, based upon the distinct phenotype and the involvement of the cardiovascular system. Tumor development is a rare manifestation of Noonan syndrome but can be explained by the molecular pathophysiology involved in the disorder. We present three Noonan patients who developed solid tumors. The first patient, a 4-year-old girl, developed granular cell tumors as did her mother in childhood. The second patient, a 1-year-old boy, had a low grade pilocytic astrocytoma, the clinical expression of which was persistent headache. MRI showed a pituitary mass in the posterior lobe. It was surgically removed. The third patient, a 7-year-old boy was found to have Sertoli tumors in his right cryptorchid testis. All three patients fulfilled the clinical criteria for Noonan syndrome. However, genetic testing was negative in patients 1 and 3. The diagnosis of Noonan syndrome was made based on distinct phenotypic findings in three patients who had different types of tumors.