Molecular Diagnosis and Phenotypic Variability of Noonan Syndrome: Experience from a Romanian Multicenter Study

Background: RASopathies represent a clinically and genetically diverse group of syndromes resulting from germline mutations in genes regulating the RAS/mitogen-activated protein kinase (MAPK) signaling cascade. Methods: The aim of this study was to describe the clinical features and genetic variants identified in patients with genetically confirmed Noonan syndrome (NS) in a limited cohort from Romania. A total of 25 patients with positive genetic testing for NS-associated genes were included. Genetic testing was performed primarily using next-generation sequencing. Results: A total of twenty-six variants were identified in twenty-five patients, as one patient carried two pathogenic variants in the PTPN11 gene (c.188A>G and c.922A>G). Of these variants, twenty-four (92.31%) were classified as pathogenic and two (7.69%) as variants of uncertain significance (VUS). Pathogenic variants were found in different genes, including PTPN11, LZTR1, SOS1, and RAF1, with PTPN11 being the most frequently affected gene. Males predominated (17/25), with a male-to-female ratio of approximately 2:1. Two patients inherited the pathogenic variant from an affected parent. Cardiovascular involvement was present in 21 patients (84%), with pulmonary valve stenosis (PVS) being the most common finding (48%), followed by hypertrophic cardiomyopathy (16%). Additional cardiac anomalies included atrial septal defect, valvular regurgitation, dysplastic valves, coarctation of the aorta, and sinotubular junction narrowing. Short stature was observed in 64% of patients, and craniofacial dysmorphism was present in 96%. Cutaneous, ectodermal, dental, ophthalmologic, and auditory manifestations were variably observed. Conclusions: Although based on a limited cohort from Romania, this study provides insights into clinical features suggestive of NS. Our findings highlight the genetic heterogeneity of NS and emphasize the importance of comprehensive genetic testing for confirming diagnosis, guiding clinical management, and supporting family counseling.