HTT and Huntington disease: While loss of HTT function is not sufficient to cause HD, given that genetic mutation or deletion of HTT alleles in human disorders including Wolf-Hirschhorn Syndrome (Battaglia et al., 2015) do not cause a neurodegenerative disease, the CAG repeat expansion does cause an apparent disruption of normal HTT functions, including synapse formation and altered neurodevelopment among other disrupted processes (Gauthier et al., 2004; McKinstry et al., 2014; Ruzo et al., 2018; Martinez-Vicente et al., 2010; Braz et al., 2022).