**Question:** Adult polycystic kidney is inherited as:

A. Autosomal Dominant
B. Autosomal Recessive
C. X-linked Recessive
D. Mitochondrial

**Core Concept:**
Adult Polycystic Kidney Disease (PKD) is a group of genetic disorders characterized by the formation of numerous fluid-filled cysts within the kidneys. These cysts progressively enlarge and damage the normal renal tissue, leading to a decline in kidney function over time. PKD can be inherited through different patterns:

1. **Autosomal Dominant (A):** In this mode of inheritance, one copy of the mutated gene is sufficient to cause the disease. The affected parent has a 50% chance of passing the disease to each offspring.
2. **Autosomal Recessive (B):** In this mode, both copies of the mutated gene (from both parents) are required to cause the disease. Offspring from such parents have a 25% chance of being affected, a 50% chance of being carriers, and a 25% chance of being unaffected.
3. **X-linked Recessive (C):** PKD caused by mutations on the X-chromosome is rare and affects primarily males. Males with the disease have a 50% chance of passing it to their sons and a 50% chance of passing it to their daughters, who will be carriers.
4. **Mitochondrial (D):** PKD caused by mutations in mitochondrial DNA is even rarer and typically presents with a more severe phenotype.

**Why the Correct Answer is Right:**

A) Autosomal Dominant inheritance (Option A) is the most common mode of inheritance in PKD. The affected parent usually does not exhibit symptoms, allowing a significant number of carriers among family members.

B) Autosomal Recessive inheritance (Option B) is less common but still relevant, especially when considering the possibility of consanguineous marriages in certain populations.

C) X-linked Recessive inheritance (Option C) is uncommon but important to consider when studying the pedigree of the affected individual.

D) Mitochondrial inheritance (Option D) is very rare and should be considered in cases with severe disease presentation or atypical inheritance patterns.

**Why the Wrong Answers are Incorrect:**

A) Mitochondrial inheritance (Option D) is incorrect due to the rarity of this mode of inheritance and its association with severe phenotypes. PKD caused by mitochondrial mutations usually presents with a more severe disease course.

B) X-linked Recessive inheritance (Option C) is incorrect as it is less common and primarily affects males. However, it is still worth mentioning for pedigree analysis in certain populations.

C) Mitochondrial inheritance (Option D) is incorrect due to the rarity of this mode of inheritance and the association with severe phenotypes.

**Clinical Pearls:**

- Inherited PKD can be classified as Autosomal Dominant (ADPKD), Autosomal Recessive (ARPKD), X-linked Recessive (X-linked PKD), and Mitochondrial PKD.