Paternal vs maternal inheritance

If you inherit the HD-causing gene from your father, the number of CAG repeats may be the same as his or higher, expanding as the gene is passed from father to child. But if you inherit the gene from your mother, the number of CAG repeats will be the same as hers or less.

This is bc men are always producing new sperm and every sperm has a random cag count of the hd causing gene. Whereas women are born with the number of eggs they have and their cag count matches the mother.

More information here: https://health.ucdavis.edu/huntingtons/genetic-change.html#:~:text=Paternal%20Inheritance&text=If%20you%20inherit%20the%20HD,CAG%20repeats%20usually%20remains%20stable.

Edit: “Mutation in HTT gene results in abnormally long polyglutamine repeats. The sex of the transmitting parent is the major determinant of intergenerational changes. In paternal transmission, the CAG repeats often increases from generation to generation (anticipation phenomenon).”

• https://www.jneurology.com/articles/maternally-inherited-huntington-disease-and-paternally-inherited-neurofibromatosis-type1-in-an-individual-a-rare-cooccurrence.html#:~:text=Mutation%20in%20HTT%20gene%20results,to%20generation%20(anticipation%20phenomenon).