**Core Concept**
Autosomal dominant disorders are characterized by the presence of a single copy of a mutated gene that causes the disease, with each parent having a 50% chance of passing the mutation to their offspring. These disorders are typically more common in males and females, with no gender predilection.

**Why the Correct Answer is Right**
Autosomal dominant disorders result from mutations in genes that encode proteins essential for normal cellular function. The presence of a single mutated allele is sufficient to cause the disease, as the normal allele is often recessive. Examples of autosomal dominant disorders include Huntington's disease, neurofibromatosis type 1, and Marfan syndrome.

**Why Each Wrong Option is Incorrect**
**Option A:** This is an incorrect statement. Huntington's disease is indeed an autosomal dominant disorder caused by an expansion of a CAG repeat in the huntingtin gene. The presence of this mutation leads to the degeneration of neurons in the brain, resulting in chorea, cognitive decline, and psychiatric problems.
**Option B:** This statement is also incorrect. Neurofibromatosis type 1 is an autosomal dominant disorder caused by mutations in the NF1 gene, which encodes a tumor suppressor protein. The loss of function of this protein leads to the development of multiple neurofibromas, cafe-au-lait spots, and other systemic manifestations.
**Option C:** This option is incorrect as well. Marfan syndrome is an autosomal dominant disorder caused by mutations in the FBN1 gene, which encodes a protein called fibrillin-1. The disruption of fibrillin-1 leads to the formation of abnormal elastic fibers in connective tissue, resulting in the characteristic features of Marfan syndrome, including tall stature, arachnodactyly, and aortic root dilatation.

**Clinical Pearl / High-Yield Fact**
Autosomal dominant disorders often have a high degree of penetrance, meaning that individuals with the mutation will almost certainly develop the disease. However, the age of onset and severity of the disease can vary widely among affected individuals.

**Correct Answer: A.**