Huntington’s disease (HD) is one of the most well defined “repeat diseases”, associated with a short repeated genetic sequence, CAG.First, taking into account that a phenocopy of HD has a different repeat that is associated with a different gene, I suggest that the gene is not important for HD, only the repeat sequence is important, in agreement with Lee et al (2019) who reached the same conclusion using a GWAS technique.Second, taking into account that a phenocopy of HD has a CTG repeat rather than a CAG repeat, and that the toxin should be the same for both disease types and that the third base in a codon is the least important, I suggest that the reading frame is shifted for the repeat expansions and that the A/T substitution takes place on the third base. The most likely sense and antisense reading frames are then (GCA)_n and (GCT)_n and (GCT)_n and (GCA)_n and the corresponding amino acid is polyalanine.Third, the more repeats, the earlier the HD onset (Brinkman et al, 1997; Wexler, 2004). I suggest that this relationship can be thought of as a rate equation. If the concentration is proportional to the probability of creating a polyalanine of length m in a repeat expansion of length n, the corresponding equation is borne out by the data on age of onset and repeat length and m is found to be about 30.6. This explains for the first time, at least approximately, why HD is not active unless there are at least 36 CAG repeats.If true, HD may be the first disease where frameshifting is the cause of the disease.