**Question:** Which of the following is a Polygenic disorder:

A. Autism
B. Cystic Fibrosis
C. Type 2 Diabetes
D. Vitamin D Deficiency

**Core Concept:** A polygenic disorder is a condition caused by the interaction of multiple genes, each with a small effect on the phenotype. Unlike monogenic disorders, the inheritance pattern is not straightforward, and the contribution of genetic variants can vary between individuals.

**Why the Correct Answer is Right:**

B. Cystic Fibrosis

Cystic Fibrosis is a polygenic disorder caused by mutations in the CFTR gene, which encodes a protein responsible for regulating the movement of chloride ions across cell membranes. The disease results from an imbalance in chloride ion transport, leading to the accumulation of thick, sticky mucus in various organs, particularly the lungs and pancreas. The inheritance pattern in Cystic Fibrosis is autosomal recessive, meaning that an affected individual must inherit two mutated copies of the CFTR gene from both parents.

**Why Each Wrong Option is Inaccurate:**

A. Autism: Autism spectrum disorder (ASD) has a complex etiology involving genetic, environmental, and epigenetic factors. The genetic basis is not polygenic but involves multiple genes, some of which are related to synaptic function, neuronal migration, and immune system development. ASD inheritance patterns are diverse, including autosomal dominant, autosomal recessive, and X-linked.

C. Type 2 Diabetes: Type 2 Diabetes is primarily a result of insulin resistance and beta-cell dysfunction, rather than mutations in multiple genes. Inheritance patterns for Type 2 Diabetes include both autosomal dominant and recessive, as well as mitochondrial inheritance.

D. Vitamin D Deficiency: Vitamin D deficiency is primarily caused by inadequate exposure to sunlight or dietary intake, rather than mutations in multiple genes. The inheritance pattern is not related to polygenic disorders.

**Clinical Pearl:** Polygenic disorders are a significant area of study in genetic counseling and gene mapping. Understanding the inheritance patterns and gene interactions involved in polygenic disorders can help healthcare professionals predict disease risks, provide appropriate genetic counseling, and guide family planning decisions.