One of us must have it.
An extremely common feeling or misunderstanding among brothers and sisters at risk for Huntington’s disease is that one of them must have it. But that’s absolutely not the case: each individual has a separate 50/50 chance of inheriting Huntington’s disease. For example, if there are 10 siblings in a family who all have a 50% risk, it does not mean that 5 of them must have the expanded Huntington’s disease gene – the science does not work like that. Because each individual has their own 50/50 risk, there is absolutely no predicting how many out of those 10 siblings have or haven’t inherit an expanded gene.
Many young people, who know and understand that each individual has their own 50/50 risk, find it doesn’t stop them from thinking that siblings’ risks must be linked.
For example, in a family with a brother and sister at-risk, if the brother decides to be tested and receives a negative result (meaning they won’t get Huntington’s disease) the sister may start to think that she must have inherited it instead.
As mentioned above, this is simply not the case so it’s very important to remember that each person has his or her own separate 50/50 risk.