Huntington's disease is caused by a single mutation in someone's DNA.
A normal protein, huntingtin, becomes warped and toxic. Over time, the toxic protein builds up, killing a person's brain cells and slowly robbing them of cognitive and motor control.
It affects about 30,000 Americans, often shows up later in life, and is fatal. Because it's a genetic disease, it can be passed down through families. It's cruel, unfair, and nobody deserves it.