Variants of the PTPN11 Gene in Mexican Patients with Noonan Syndrome

<b>Background/Objectives:</b> Noonan syndrome (NS) is a genetic multisystem disease characterized by distinctive facial features, short stature, chest deformity, and congenital heart defects. NS is caused by gene variants of the RAS/MAPK pathway, with <i>PTPN11</i> accounting for about 50% of cases. This study aimed to identify <i>PTPN11</i> pathogenic variants in Mexican patients with NS to enhance our understanding of the disease in this population. <b>Methods</b>: This study included 91 probands and 60 relatives, all of which were clinically evaluated by a geneticist. Sanger sequencing was used to screen the entire <i>PTPN11</i> gene. <b>Results</b>: Twenty-one previously reported pathogenic variants were identified in 47.3% of the probands. The most frequently occurring were p.Asn308Asp (16.3%) and p.Met504Val (16.3%). Variants p.Tyr279Cys and p.Thr468Met were found exclusively in patients with lentiginosis. Eighty-three percent of patients carried a variant in one of the three exons (3, 8, or 13) where the greatest genetic diversity was observed. Common clinical findings identified in probands included short stature (82%), cardiac anomalies (70.7%), short neck (68.4%), and <i>pectus excavatum</i> (63.2%), although features represented by only one patient each were also detected. <b>Conclusions</b>: This study confirmed the clinical diagnosis of NS in 43 probands and 11 relatives, and further genetic analysis of the remaining 48 probands is required to identify the causal variant. The genetic and clinical variability observed in our cohort was consistent with reports from other populations, underscoring the importance of comprehensive care for all patients. This research provides the most extensive clinical and molecular characterization of NS in Mexican patients, identifying pathogenic variants of <i>PTPN11</i>.