Noonan Syndrome With Complex Pulmonary Stenosis at High Altitude: Impact of Delayed Diagnosis

Noonan syndrome is a genetic disorder affecting 1 in 1,000 to 2,500 live births, with cardiac involvement in up to 80% of cases, predominantly pulmonary valve stenosis. Socioeconomic barriers often delay diagnosis in resource-limited settings.

A 22-year-old male presented with severe oxygen desaturation at high altitude, initially attributed to COVID-19. Clinical evaluation revealed characteristic Noonan syndrome features and a grade IV/VI systolic murmur. Cardiac imaging demonstrated severe dysplastic pulmonary stenosis with supravalvular membrane, right-to-left shunting through an atrial septal defect, and an anomalous right coronary artery. The patient underwent pulmonary valve replacement, right ventricular outflow-tract enlargement, atrial septal defect closure, and unplanned aortic valve replacement for unexpected moderate insufficiency. Despite postoperative complications, 4-year follow-up showed excellent outcomes.

This case illustrates how high-altitude physiology exacerbates right-to-left shunting in congenital heart disease and highlights how socioeconomic barriers delay critical interventions, emphasizing the need for improved healthcare accessibility in marginalized populations.