Adult polycystic kidney disease is inherited: March 2005
**Core Concept**
Adult polycystic kidney disease (APKD) is a genetic disorder characterized by the growth of numerous cysts filled with fluid in the kidneys, leading to kidney enlargement and impaired kidney function. It is caused by mutations in the PKD1 or PKD2 genes, which encode for polycystin-1 and polycystin-2 proteins, respectively. These proteins play a crucial role in maintaining the structural and functional integrity of the renal epithelium.
**Why the Correct Answer is Right**
APKD is inherited in an autosomal dominant pattern, meaning that a single copy of the mutated gene is sufficient to cause the condition. This means that if one parent has APKD, each child has a 50% chance of inheriting the mutated gene and developing the condition. The PKD1 gene is responsible for approximately 85% of APKD cases, while the PKD2 gene accounts for the remaining 15%. The mutated genes lead to the formation of cysts due to defective cellular transport and signaling mechanisms.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because APKD is not inherited in an autosomal recessive pattern, which would require two copies of the mutated gene (one from each parent) to cause the condition.
**Option B:** This option is incorrect because APKD is not inherited in an X-linked pattern, which would involve genes located on the X chromosome. APKD primarily affects both males and females equally, making X-linked inheritance unlikely.
**Option C:** This option is incorrect because APKD is not inherited in a mitochondrial pattern, which would involve genes located in the mitochondria. APKD is primarily a nuclear gene disorder, and its inheritance pattern is autosomal dominant.
**Clinical Pearl / High-Yield Fact**
It is essential to remember that APKD is often asymptomatic until late in life, making regular screening and monitoring crucial for early detection and management. A family history of APKD is a significant risk factor, and individuals with a family history should undergo regular kidney function tests and imaging studies to detect any potential issues early.
**Correct Answer: C. Autosomal dominant.**