HD and nor will any of their children. 2.Gene-positive: If at least one copy of a person's HD gene contains 40 or more CAG repeats they will develop HD in their lifetime and each of their children have a 50% risk of inheriting HD. 3.'Reduced penetrance' range: People with a HD gene containing between 36 and 39 repeats are in the 'reduced penetrance' range. Some people in this range will develop symptoms of the disease, while others won't and there is still a risk of their children inheriting the disease. 4.'Intermediate alleles' range: People in this range have repeat lengths between 27 and 35 CAGs. People with an intermediate allele will not develop HD themselves, but there may be a risk of HD developing in their children. It may be the case that one of your parents has a CAG repeat length that falls either in the 'reduced penetrance' range or the 'intermediate alleles' range. If this is the case, it means that even though they have not shown any signs of HD all of their children have a reduced risk (less than 50%) chance of of inheriting the disease. If you are worried about the implications that this has for you and your family it may be helpful to speak to your local HD association. All the best. When CAG repeats are at birth itself why it shows symptoms in mid 30-40 of age? - Archana (42) Hi Archana, Symptoms of Huntington's Disease (HD) can begin at any age;