When someone has Huntington's disease, part of the DNA sequence: (CAG: Cytosine — Adenine — Guanine) repeats more times than normal.
It is important to understand that everyone on the planet is born with the Huntingtin gene. The healthy gene repeat averages around 17, however, a person's CAG repeat can range from less than 10 to more than 120. There are two forms of this disease: Adult on-set Huntington's disease, and Juvenile Huntington's disease. It is important to note that every person on the planet has the Huntington gene.
As per HDYO > https://en.hdyo.org/eve/articles/53
Dr. Peg Nopoulos of the University of Iowa (Kids-HD/Kids-JHD discusses CAG
A clip from "The Purple Road" Juvenile Huntington's disease documentary. Dr. Peg Nopoulos of the University of Iowa (Kids-HD/Kids-JHD discusses the differences between HD and JHD.