In classical Mendelian inheritance, autosomal dominant disease characterized by:
**Core Concept**
Autosomal dominant diseases are a type of genetic disorder caused by mutations in one of the two copies of a gene. This means that a single copy of the mutated gene is sufficient to cause the disease, and affected individuals have a 50% chance of passing the mutated gene to each offspring. Autosomal dominant diseases can affect anyone, regardless of their sex or family history.
**Why the Correct Answer is Right**
The correct answer is Marfan syndrome, a genetic disorder that affects the body's connective tissue. It is caused by mutations in the FBN1 gene, which codes for fibrillin-1, a protein essential for the formation of elastic fibers in connective tissue. Marfan syndrome affects various parts of the body, including the heart, eyes, skeleton, and blood vessels. The disease is characterized by tall stature, long limbs, and aortic root dilatation, among other features.
**Why Each Wrong Option is Incorrect**
**Option A:** **Huntington's disease** is an autosomal dominant disorder, but it is characterized by progressive damage to the brain, leading to cognitive decline, motor dysfunction, and psychiatric problems. It is caused by an expansion of a CAG repeat in the HTT gene.
**Option B:** **Tay-Sachs disease** is an autosomal recessive disorder, not autosomal dominant. It is caused by a deficiency of the enzyme hexosaminidase A, leading to accumulation of GM2 ganglioside in neurons and resulting in neurodegeneration.
**Option C:** **Sickle cell disease** is an autosomal recessive disorder, not autosomal dominant. It is caused by a mutation in the HBB gene, leading to production of abnormal hemoglobin S (HbS) that causes red blood cells to become sickle-shaped and prone to hemolysis.
**Clinical Pearl / High-Yield Fact**
Autosomal dominant diseases often have a high degree of penetrance, meaning that the majority of individuals with the mutated gene will develop the disease. However, the age of onset and severity of the disease can vary widely among affected individuals.
**Correct Answer: C. Marfan syndrome**