While mutant HTT causes late-onset neurodegeneration in HD, it has been found to affect neuronal cells during early brain development (Reiner et al., 2003; Godin et al., 2010; McKinstry et al., 2014; Molina-Calavita et al., 2014; Molero et al., 2016; Barnat et al., 2020; Mangin et al., 2020; Capizzi et al., 2022). The gene discussed is HTT; the disease is Huntington disease.