**Core Concept**
Peripheral pulmonic stenosis, also known as peripheral pulmonary artery stenosis, refers to a narrowing of the peripheral pulmonary arteries, which supply blood to the lungs. This condition can lead to increased pulmonary vascular resistance and right ventricular outflow obstruction.

**Why the Correct Answer is Right**
William syndrome, also known as Williams-Beuren syndrome, is a genetic disorder characterized by supravalvar aortic stenosis, peripheral pulmonic stenosis, and other systemic features. The condition results from a deletion of genetic material on chromosome 7, leading to the overexpression of the elastin gene, which causes elastic fiber abnormalities in the aortic and pulmonary arteries. This results in the narrowing of the peripheral pulmonary arteries, characteristic of peripheral pulmonic stenosis.

**Why Each Wrong Option is Incorrect**
**Option A:** Subaortic stenosis is a narrowing of the left ventricular outflow tract, below the aortic valve, and is not associated with peripheral pulmonic stenosis.

**Option B:** Takayasu's arteritis is a large vessel vasculitis that primarily affects the aorta and its major branches, but not typically the peripheral pulmonary arteries.

**Option D:** Coarctation of the aorta refers to a narrowing of the aortic isthmus, which can lead to hypertension and other cardiovascular complications, but is not directly associated with peripheral pulmonic stenosis.

**Clinical Pearl / High-Yield Fact**
Peripheral pulmonic stenosis is a common feature of Williams syndrome, along with supravalvar aortic stenosis. Recognizing this association is crucial for diagnosing and managing patients with Williams syndrome.

**✓ Correct Answer: C. William syndrome**