Huntington's disease is an inherited disease of the brain that damages certain brain cells.
The disease damages some of the nerve cells in the brain, causing deterioration and gradual loss of function of these areas of the brain. This can affect movement, cognition (perception, awareness, thinking, judgement) and behaviour.
Early symptoms can include personality changes, mood swings and unusual behaviour, although these are often overlooked and attributed to something else.
Juvenile (children's) Huntington's disease develops before the age of 20. Only 5-10% of people with Huntington's develop the condition at a very young age, and the pattern of features may be different.
Huntington's disease was originally called Huntington's chorea ("chorea" is the Greek word for dancing). This is because the involuntary movements associated with the condition can look like jerky dancing. However, "disease" is now the preferred term, because the condition involves a lot more than just abnormal movements.
Huntington's disease is caused by an inherited faulty gene. However, in around 3% of cases, there's no family history of the condition, normally because the parents died at a young age.