Which condition is known for degeneration of the nervous system and is caused by a dominant allele?

Huntington's disease is a neurodegenerative disorder that is caused by a dominant allele located on chromosome 4. This condition is characterized by the progressive breakdown of nerve cells in the brain, leading to cognitive decline, motor dysfunction, and emotional disturbances. The dominant nature of the allele means that only one copy of the mutated gene is necessary for an individual to develop the disease, resulting in a 50% chance of passing the disorder to offspring if one parent is affected. This inheritance pattern distinguishes it from disorders like muscular dystrophy and Alzheimer's disease, which involve different genetic mechanisms and are not primarily caused by a dominant allele. Understanding the genetic basis of Huntington's disease is crucial for both diagnosis and potential genetic counseling for families affected by this condition.