well can protect the brain from neural loss caused by HD and maybe delay symptom onset and disease progression. So there are a few factors which are variable regarding your boyfriend: 1. He may not test gene-positive (50% chance) which means he will not have to worry about HD symptoms himself or passing the faulty gene on to any children he has. 2. If he is gene-positive his CAG repeat length could be less, more or the same as his fathers which will contribute to his age of symptom onset. 3. The age of symptom onset may be affected by the lifestyle he leads. 4. The age of symptom onset may be affected by other genes. Thanks again for your question and hopefully our response was helpful. "Hi, Why does Huntington's disease occur at a late age?" - Shahan (17) Hi Shahan, Ultimately, the mutant Huntingtin protein which is produced in Huntington's Disease 'overworks' the cells is our body and eventually causes more and more cells in the brain to die over a person's life span. Symptoms become noticable when a certain amount of neural death has occurred. HD can occur at any age, but most often comes on between 35 & 55. The size of the gene fault (the number of CAG repeats) is a major factor, but not the only factor. Current research is investigating other influences on the age at which people get HD might be, which includes the effects of other genes & perhaps also lifestyle.