**Question:** The following are inherited as autosomal recessive disorder except

A. Cystic Fibrosis
B. Sickle Cell Anemia
C. Tay-Sachs Disease
D. Marfan Syndrome

**Correct Answer:** D. Marfan Syndrome

**Core Concept:**
Autosomal Recessive Disorders:
Autosomal recessive disorders are genetic conditions that are inherited when an individual inherits two copies of the mutated gene, one from each parent. These conditions typically occur when both parents are carriers of the mutated gene but are not affected by the disorder themselves. In such cases, the child has a 25% chance of inheriting the condition, a 50% chance of being a carrier, and a 25% chance of not inheriting the gene at all.

**Why the Correct Answer is Right:**
Marfan Syndrome is an example of an autosomal dominant disorder, not a recessive one. In autosomal dominant disorders, an individual only needs to inherit one mutated gene to develop the condition. Since the inheritance pattern is different, Marfan Syndrome is not considered an autosomal recessive disorder.

**Why Each Wrong Option is Incorrect:**

A. Cystic Fibrosis: This condition is also inherited as an autosomal recessive disorder.
B. Sickle Cell Anemia: This is an autosomal recessive disorder involving the HBB gene on chromosome 11.
C. Tay-Sachs Disease: This is an autosomal recessive disorder caused by mutations in the HEXA gene on chromosome 15.

**Clinical Pearl:**
Autosomal Recessive Disorders:
Autosomal recessive disorders are a diverse group of conditions that affect various systems in the body. Some examples include sickle cell anemia, Tay-Sachs Disease, and Cystic Fibrosis. Understanding the inheritance patterns of genetic disorders is crucial for genetic counseling, prenatal diagnosis, and disease management. Familiarize yourself with the different inheritance patterns, such as autosomal dominant, autosomal recessive, X-linked, mitochondrial, and X-linked dominant.

By understanding these patterns, healthcare professionals can provide accurate information to families regarding the risk of passing on these conditions to their children and help them make informed decisions about reproductive choices.