**Core Concept**
Noonan's syndrome is a genetic disorder characterized by distinctive facial features, short stature, heart defects, and bleeding problems. It is caused by mutations in genes that regulate cell growth, differentiation, and signaling pathways.

**Why the Correct Answer is Right**
Noonan's syndrome often presents with cardiovascular abnormalities, including pulmonary valve stenosis, septal defects, and hypertrophic cardiomyopathy. The syndrome also increases the risk of bleeding due to platelet dysfunction and thrombocytopenia. Additionally, affected individuals may experience developmental delays, intellectual disability, and skeletal abnormalities.

**Why Each Wrong Option is Incorrect**
**Option A:** While Noonan's syndrome is associated with bleeding problems, it is not typically associated with thrombocytosis, which is an increase in platelet count. This option is incorrect because Noonan's syndrome is characterized by thrombocytopenia, not thrombocytosis.

**Option B:** Individuals with Noonan's syndrome are at risk for developing heart defects, including septal defects. This option is incorrect because septal defects are a known association with Noonan's syndrome.

**Option C:** While Noonan's syndrome is associated with various physical abnormalities, including distinctive facial features, it is not typically associated with obesity. This option is incorrect because Noonan's syndrome is more commonly associated with short stature and underweight status.

**Clinical Pearl / High-Yield Fact**
Noonan's syndrome is an autosomal dominant disorder, meaning that a single copy of the mutated gene is sufficient to cause the condition. This is an important clinical correlation to remember when evaluating patients with suspected Noonan's syndrome.

**Correct Answer: D. Obesity**