Huntington's disease is due to an expansion of repeated CAG triplets (at 36 or more repeats) on the short arm of chromosome 4 in the HTT gene of huntingtin.
The prevalence in the Caucasian population is estimated at 1 / 20,000 to 1 / 10,000. This is higher compared to a disease with autosomal recessive inheritance.
It should be known that this disease affects only certain families where a heterozygote has a chance to transmit it (1/2), this is due to a mutation in their gene.
Despite its dominant character, it remains a rare disease due to its recent appearance (discovered in the 19th century) and also the rarity of the mutation.