**Question:** The following condition is not a single gene disorder

A. Cystic Fibrosis
B. Diabetes Mellitus Type 1
C. Duchenne Muscular Dystrophy
D. Autism Spectrum Disorder

**Core Concept:** A single gene disorder is a condition caused by mutations in a single gene, leading to an altered protein function or production. Examples include hemophilia, sickle cell anemia, and cystic fibrosis.

**Why the Correct Answer is Right:** Duchenne Muscular Dystrophy (C) is a genetic disorder caused by mutations in the dystrophin gene, leading to a deficiency of dystrophin protein. This results in progressive muscle weakness and degeneration.

Diabetes Mellitus Type 1 (B) is an autoimmune disease where the pancreas produces little or no insulin, leading to high blood sugar levels. It is not caused by a single gene mutation, but rather an interaction between genetic and environmental factors.

Autism Spectrum Disorder (D) is a complex neurodevelopmental disorder with a combination of genetic, environmental, and epigenetic factors contributing to its etiology. It is not caused by a single gene mutation.

**Why Each Wrong Option is Incorrect:** Cystic Fibrosis (A) is a single gene disorder caused by mutations in the CFTR gene, leading to the production of a defective or absent chloride channel protein. This results in impaired mucus clearance, leading to lung infections and other severe complications.

Diabetes Mellitus Type 1 (B) and Autism Spectrum Disorder (D) involve a combination of genetic, environmental, and epigenetic factors, making them complex conditions. They are not exclusively caused by mutations in single genes.

Duchenne Muscular Dystrophy (C) is also a genetic disorder but is caused by mutations in the DMD gene, which encodes dystrophin protein. The correct answer is Duchenne Muscular Dystrophy (C) because it is caused by a single gene mutation, whereas the other options involve a combination of factors and are not single gene disorders.

**Clinical Pearl:** Understanding the etiology of complex disorders like Diabetes Mellitus Type 1 and Autism Spectrum Disorder is crucial for effective patient care and counseling. It is essential to differentiate these conditions from single gene disorders like Cystic Fibrosis and Duchenne Muscular Dystrophy. This helps in appropriate diagnosis, prognosis, and management strategies for patients with these conditions.