HTT and epilepsy: Thus, in HD, modest expansions of 40 repeats in huntingtin gene (HTT) are associated with the appearance of motor, cognitive, and psychiatric disturbances in mid- or late adulthood, whereas large expansions of over 80 repeats cause childhood onset with additional features such as epilepsy and a more rapidly fatal course (Bates et al., 2015b; Sun et al., 2017).