get HD rather than telling you the age of onset. People with a CAG number of 36 to 39 have a less than 100% chance of getting HD and the average age of onset is higher than for people with 40 or more CAG repeats. If the CAG number is 40 or more then the life long chance of getting HD is effectively 100%, but again the age of onset will vary widely from early adulthood to old age. The CAG number does not influence the initial symptoms of HD, as far as we know. That is, one person with  a particular CAG number might first get chorea whereas another person with the same CAG number might develop anxiety & depression. We don't know why there is so much variation in the age of onset or the initial symptoms. Probably there are other genes, most of which have not been found, that might have an influence on age of onset. Lifestyle might also be important. There is quite a lot of evidence that physical and mental activity in general might delay onset of HD.  Physical and mental activity is also fun and is good for health in other ways like keeping your weight down & protecting you from diabetes and high blood pressure. I recommend to my gene positive patients that they exercise for about 20 or 30 minutes three times a week and keep their minds active. Andrew my dad has huntingtons disease and my grandad did and do