**Core Concept**
Berry aneurysms are small, saccular aneurysms typically found at arterial branching points, particularly in the anterior circulation. They are a common cause of subarachnoid hemorrhage (SAH) due to rupture.

**Why the Correct Answer is Right**
Berry aneurysms are characterized by their thin, fragile walls, which are composed of elastic lamina and tunica media, but not smooth muscle cells or fibroblasts. Unlike other types of aneurysms, berry aneurysms lack a thick muscular wall that would provide additional structural support.

**Why Each Wrong Option is Incorrect**
**Option A:** Berry aneurysms are indeed associated with familial syndromes, such as polycystic kidney disease (PKD) and Ehlers-Danlos syndrome, making this statement true. However, it is not the correct answer to the question asking for what is "except."
**Option B:** The most common site of rupture for berry aneurysms is indeed the apex, which causes SAH, making this statement true. However, it is not the correct answer to the question asking for what is "except."
**Option D:** Berry aneurysms typically occur at the anterolateral portion of the circle of Willis, particularly at branching points, making this statement true. However, it is not the correct answer to the question asking for what is "except."

**Clinical Pearl / High-Yield Fact**
Berry aneurysms are more common in women, particularly in the 4th and 5th decades of life. They are often asymptomatic until rupture, which can lead to SAH, a life-threatening condition requiring prompt medical attention.

**✓ Correct Answer:** C. Wall contains smooth muscle fibroblasts