What gene or chromosome is affected by huntington's disease?

Answer: HD gene.

Explanation:

The HD gene's mutation results in Huntington disease. It was mapped to chromosome 4 in 1983. HD is known as the quintessential family disease where there is a 50/50 chance of carrying a faulty gene to the subsequent generations. It is a fatal genetic progressive disorder that causes uncontrolled movements, emotional problems, and loss of thinking ability due to progressive breakdown of nerve cells in the brain.