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

A. Autosomal dominant
B. Autosomal recessive
C. X-linked dominant
D. X-linked recessive

**Correct Answer:**

**Core Concept:**

Adult polycystic kidney disease (PKD) is a group of inherited kidney disorders characterized by the formation of multiple fluid-filled sacs within the kidneys, leading to impaired kidney function and potential end-stage renal disease. PKD can be inherited through different genetic modes, which are the basis for distinguishing between the four options provided.

**Why the Correct Answer is Right:**

Adult polycystic kidney disease (PKD) is inherited as **Autosomal dominant**. In this mode of inheritance, the affected gene is located on an autosome, and an affected parent has a 50% chance of passing the disease to each of their children. If an affected parent has one copy of the mutated gene and one copy of the normal gene, their children inherit the same combination of genes. This means that an affected person has a 50% chance of passing the disease to their offspring.

**Why Each Wrong Option is Incorrect:**

**Option A (Autosomal recessive):** PKD is not inherited in an autosomal recessive manner, as the disease would affect an equal number of males and females. Autosomal dominant PKD is more likely to affect males and females equally.

**Option B (X-linked dominant):** PKD is not inherited in an X-linked dominant manner, as the disease would affect males more severely than females, due to the presence of a single X-chromosome in males and two X-chromosomes in females. Autosomal dominant PKD is more likely to affect males and females equally.

**Option C (X-linked recessive):** PKD is not inherited in an X-linked recessive manner, as the disease would affect males twice as often as females due to the presence of a single X-chromosome in males and two X-chromosomes in females. Autosomal dominant PKD is more likely to affect males and females equally.

**Option D (Sporadic):** Sporadic PKD refers to PKD without a clear genetic basis and is not the correct mode of inheritance for this question. PKD is typically inherited through a genetic mutation.

**Clinical Pearl:** Understanding the mode of inheritance helps in counseling patients and families regarding the risk of passing the disease on to their offspring and allows for the identification of asymptomatic carriers.

**Why Core Concept is Important:**

Understanding the mode of inheritance is crucial for medical professionals working with PKD patients and their families. It helps guide genetic counseling, inform patients and families about their risk of passing on the disease, and facilitates identification of asymptomatic carriers. This knowledge also aids in diagnosing PKD and differentiating it from other kidney diseases that may have similar symptoms.