Between 5 and 8 per 100, 000 people have huntington's in europe and n.
America, less in non-european populations. Since huntington's is autosomal dominant, then if one parent has the disease, each child has a 50% chance of acquiring it. Huntington's typically appears after childbearing age, and can be misdiagnosed as a psychosis
, so absence of a family history can be hard to confirm.
Answer assisted by Aaron Stupple, Medical Student