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

A. Adult polycystic kidney disease (PKD) is caused by genetic mutations in the PKD1 or PKD2 genes.
B. PKD primarily affects the liver and pancreas, and kidney involvement is a late complication.
C. PKD is a rare disorder with a prevalence of less than 1%.
D. PKD is a benign condition with no progression or complications.

**Correct Answer: A. Adult polycystic kidney disease (PKD) is caused by genetic mutations in the PKD1 or PKD2 genes.**

**Core Concept:**
Adult polycystic kidney disease (PKD) is a genetic disorder characterized by the formation of numerous fluid-filled cysts in the kidneys, leading to progressive renal dysfunction and failure. PKD is classified into two main types:

1. Autosomal dominant polycystic kidney disease (ADPKD), caused by mutations in the PKD1 or PKD2 genes, which encode polycystin-1 and polycystin-2 proteins involved in cell signaling pathways regulating kidney development and function.
2. Autosomal recessive polycystic kidney disease (ARPKD), caused by mutations in the PKHD1 gene, which encodes fibrocystin protein essential for renal tubule development and function.

**Why the Correct Answer is Right:**
ADPKD and ARPKD are genetic disorders with distinct gene mutations causing cyst formation in the kidneys. In the case of ADPKD, mutations in PKD1 or PKD2 lead to impaired cell signaling pathways, causing the cyst formation. In ARPKD, mutations in PKHD1 lead to fibrocystin deficiency, which affects renal tubule development and function.

**Why Other Options are Incorrect:**

**B. PKD primarily affects the liver and pancreas, and kidney involvement is a late complication:**
While PKD can involve the liver and pancreas, the primary focus of the question is on the kidneys. PKD's late kidney involvement is attributed to the progressive cyst formation and damage to functional nephrons, leading to reduced renal function and potential end-stage renal disease.

**C. PKD is a rare disorder with a prevalence of less than 1%:**
PKD is relatively common, affecting approximately 1 in 1,000 individuals, making it a relatively common genetic disorder. The prevalence of 1% is incorrect.

**D. PKD is a benign condition with no complications:**
PKD is a progressive genetic disorder, where cyst formation leads to renal dysfunction and potential end-stage renal disease. This option highlights the benign nature, which is incorrect. PKD carries a risk of severe complications, such as hypertension, renal failure, and liver cysts.

**Why the Correct Answer is Right:**
ADPKD and ARPKD are rare genetic disorders caused by mutations in PKD1/PKD2 and PKHD1 genes, respectively. These genes are involved in regulating renal tubule development and function, leading to cyst formation and progressive renal failure.

**Clinical Pearls:**
- PKD is an