might be gene positive but have different sized CAG repeat expansions. Both might of course be gene negative. In terms of predictive testing, if one member of an identical twin pair tested positive for HD then I would recommend that the other considered getting counselling to help them work out what the result might mean to him or her. There has been one case, of Australian identical twins, who presented differently. That is, identical twins cannot assume that HD will behave in exactly the same way in both twins.  Also, the psychological impact of being gene positive might be different in each twin. These subtleties are why I'd recommend that the second identical twin might see a counsellor Andrew Churchyard I know that people who suffer from HD have a shorter life expectancy. I just don't know why that is ... what do they die from, exactly? How long do you have, from the onset of symptoms? Rachel (18) has just sent in a question. Name: Rachel Age: 18 Question: I know that people who suffer from HD have a shorter life expectancy. I just don't know why that is ... what do they die from, exactly? How long do you have, from the onset of symptoms? The answer to these 2 questions are  not as straight forward as they might seem. In general people with HD become very disabled at about 10-15 years from the onset of symptoms. However, the rate of  progression is very variable and so some