Huntington’s disease (HD) is a progressive breakdown of nerve cells in the brain. Dr. Suski said the condition broadly affects a person’s movement, thinking, and mental health. “It hits the three M’s — mood, movement, and memory,” Dr. Suski said. Many people develop symptoms in their 30s or 40s, though the disease can occur at any time in someone’s life. The life expectancy of those with adult HD is about 20 years after symptoms begin.