**Question:** Which of the following statements about adult polycystic kidney disease is true?

A. Polycystic kidney disease is a genetic disorder caused by mutations in PKD1 or PKD2 genes.
B. The disease primarily affects the liver and lungs, leading to cyst formation.
C. Adult polycystic kidney disease is a common cause of chronic kidney disease in the elderly population.
D. The condition is exclusively observed in children.

**Core Concept:** Adult polycystic kidney disease (APKD) is a genetic disorder that primarily affects the kidneys, characterized by the formation of numerous fluid-filled cysts in the renal parenchyma. This condition is usually caused by mutations in PKD1 (polycystic kidney disease 1) or PKD2 (polycystic kidney disease 2) genes, which encode for polycystin-1 and polycystin-2 proteins, respectively.

**Why the Correct Answer is Right:** APKD primarily affects the kidneys, as indicated by statement C. It is a common cause of chronic kidney disease in the elderly population due to the progressive cyst growth, which leads to impaired kidney function. While PKD1 and PKD2 mutations contribute to the development of polycystic kidney disease, it is essential to understand that the disease is *not* exclusively observed in children (option D) or primarily affects the liver and lungs (option B), as these claims are not accurate descriptions of the condition.

**Why Each Wrong Answer is Incorrect:**

**Option A:** Mentioning PKD1 and PKD2 genes is correct but does not address the primary focus on cyst formation in the kidneys, which is the core feature of APKD.

**Option B:** The disease affecting the liver and lungs is incorrect, as the primary organ affected by the disease is the kidneys, not liver or lungs.

**Option D:** Although PKD1 and PKD2 mutations can lead to APKD, stating that the disease is exclusively observed in children is not accurate. APKD can occur at any age but is more common in adults.

**Option C:** Cyst formation in the kidneys and its impact on chronic kidney disease are the main aspects of APKD, making this statement the correct answer.