Reduced Penetrance genetic test result

HD genes that have between 36–39 CAG repeats are described as having ‘reduced penetrance’. This means that while the person has a CAG size in the disease range, some people may never manifest signs and symptoms of HD, even if they live into old age (i.e., approximately 75 years). A small number of people who receive a positive predictive test result for HD fall into this reduced penetrance category.