4. Number of CAG Repeats: A Matter of Degrees
As noted, the key genetic mutation in Huntington’s disease involves an increase in CAG repeats within the HTT gene. However, the number of these repeats isn’t a binary factor. Instead, it operates on a spectrum, with more repeats correlating to earlier onset and more severe disease.
While any number above 35 CAG repeats can result in Huntington’s disease, those with 40 or more repeats will undoubtedly develop the disease. This is a hard and fast rule with Huntington’s – if you have 40 or more repeats, the disease will manifest at some point in your lifetime.
In contrast, individuals with between 36 and 39 repeats live in a state of uncertainty. Some will develop the disease, while others will not. For this group, the number of repeats can be seen as a probability factor, contributing to but not definitively causing Huntington’s disease.
Interestingly, the number of CAG repeats doesn’t only influence disease onset – it also correlates with the disease’s severity. Individuals with a higher number of repeats tend to experience a more rapid disease progression and an earlier onset of symptoms.
This characteristic highlights the overwhelming influence of this genetic mutation on Huntington’s disease. The presence and number of repeats is not just a cause but also an indicator of what individuals can expect from their disease course, underscoring the critical role of CAG repeats in Huntington’s disease diagnosis, prognosis, and management. (4)
