& have the chance to get expert advice. Dr Andrew what is considered a high cag repeat number Asked by Jill who is 16 years old. If the CAG repeat number is 40 or more, then one day the person will get symptomatic Huntington's disease (HD). The typical age of onset is from late thirties to mid-fifties. In general, the higher the CAG repeat number the earlier the age of onset. If the CAG repeat number is between 36 and 39, then there is  a less than 100% chance that the person will  develop HD and the age of onset of symptoms is often in the sixties or seventies or even older. It's important to remember that the exact repeat number doesn't reliably predict either the age of onset or the symptoms a person might get.  That is, no doctor or genetic counsellor will be able to tell a gene positive person when she or he will get symptoms. It's difficult to say what is and what is not a high CAG repeat number given that it  doesn't reliably  predict when HD will appear or how it will behave. I guess most doctors would say that if the CAG number was above 50 then that was high. However, if someone does have a CAG repeat number like that then it doesn't mean that  they will inevitably get HD early. Dr Andrew ow can i help my 16 year old grandaughter who has just been diagnosed with juvenile hd, she lives