Most common gene involved in Noonan syndrome
**Core Concept**
Noonan syndrome is a genetic disorder characterized by distinct facial features, short stature, heart defects, and developmental delays. It is caused by mutations in genes involved in the RAS-MAPK signaling pathway, which regulates cell growth and differentiation.
**Why the Correct Answer is Right**
The most common gene involved in Noonan syndrome is PTPN11, which encodes a non-receptor tyrosine phosphatase. Mutations in PTPN11 lead to the activation of the RAS-MAPK pathway, resulting in the characteristic features of Noonan syndrome. This gene is responsible for approximately 50% of cases, making it the most common genetic cause of the disorder.
**Why Each Wrong Option is Incorrect**
**Option A:** SHOC2 mutations are also associated with Noonan syndrome, but they account for a smaller proportion of cases (around 5-10%).
**Option B:** SOS1 mutations are more commonly associated with Noonan syndrome-like disorder, a distinct clinical entity.
**Option C:** RAF1 mutations are associated with Noonan syndrome, but they are less common than PTPN11 mutations.
**Clinical Pearl / High-Yield Fact**
Noonan syndrome is a significant cause of congenital heart disease, particularly pulmonary valve stenosis and hypertrophic cardiomyopathy. Patients with Noonan syndrome should undergo regular cardiac evaluations to monitor for these complications.
**Correct Answer: A. PTPN11**