HTT and Huntington disease: At present, the most widely accepted mechanism of HD is the toxic effect of mutated huntingtin (Ghosh and Tabrizi 2018; McColgan and Tabrizi 2018), although loss of wild-type huntingtin has also been considered a factor (Barron et al. 2021; Ghosh and Tabrizi 2018; McColgan and Tabrizi 2018).