Predictive Genetic Testing: The Huntington Disease Model

Abstract

Abstract Predictive or presymptomatic genetic testing enables individuals at risk for a hereditary late‐onset disease to learn about their genetic status before symptoms have appeared. The predictive testing protocol for Huntington disease (HD) safeguards the interests of test candidates and has served as a model for other diseases. Most people seen for genetic counselling regarding HD are the asymptomatic children of an affected parent. Predictive testing provides the opportunity to get relief from the anguish of being at risk, to have prenatal tests or preimplantation genetic testing, to have children free from the disorder and to make informed plans for the future regarding marriage, education, professional career and finances. The common experience has been that tested individuals found relief from their prior psychological distress and that they benefited psychologically from testing. Having children proved to be an additional stress factor for partners. Key concepts: Predictive testing provides the opportunity to get relief from uncertainty and prepare better for the future. Preimplantation genetic testing enables couples to have a pregnancy without the burden of termination after an unfavourable prenatal test result. At 55 years of age and being not symptomatic, there is still a 25% empirical chance of being a carrier of the Huntington's gene. The Huntington disease CAG repeat length accounts for roughly 50–77% of the variation in the age of onset. Predictive testing requires informed consent by the individual at risk and the provision of psychological support. Predictive testing for adult‐onset disorders without treatment options should not be offered to children and adolescents. Exclusion testing is an important option for an individual at 25% risk because the genetic status of his at‐risk parent does not need to be revealed. Counselling test candidates at 25% risk to get Huntington disease requires a family system approach. The predictive test candidate's beliefs about causation and emotional, social and cultural issues may affect the perception of the information that is given in genetic counselling.