Domain-Specific Phenotypic Profiles in RAF1-Related Noonan Syndrome

Pathogenic variants in RAF1 are a common cause of Noonan syndrome (NS), accounting for approximately 5% of cases. Nonetheless, RAF1-related NS is often associated with severe clinical features, particularly hypertrophic cardiomyopathy (HCM). Although initial studies highlighted the occurrence of genotype-phenotype correlations, a comprehensive analysis specifically focused on RAF1 variants is still lacking. We conducted a retrospective observational study combining newly collected cases of RAF1-related NS from a national multicenter retrospective cohort (RC) with systematically reviewed cases from literature search (literature cohort, LC). Variants were classified by protein domain, while the most recurrent variant, p.Ser257Leu, was analyzed separately to assess variant- and domain-specific phenotype correlations. A total of 203 cases were included. Variants in the CR2 domain accounted for 83% of cases, with p.Ser257Leu alone representing 53%. HCM was observed in 80.1% of affected individuals confirming its role as the predominant cardiac manifestation in RAF1-related NS; neurodevelopmental features were reported in 44.5% of patients. The prevalence of clinical features varied significantly according to variant location. HCM was markedly more frequently associated with CR2 variants (89.4%) and in subjects heterozygous for the p.Ser257Leu change (94.2%) compared with non-CR2 variants (37.1%). Conversely, neurodevelopmental features were more common in patients with non-CR2 variants (69.2%) than in those with CR2 variants (38.2%) or p.Ser257Leu (29.4%). CR2 and p.Ser257Leu variants were associated with earlier age at diagnosis and increased mortality. Our findings confirm and document more comprehensively domain- and variant-specific phenotypes in RAF1-related NS, emphasizing the importance of variant-level interpretation in clinical management and genetic counseling.