HTT and Huntington disease: First, the mutant HTT protein alters tau splicing, phosphorylation, oligomerization and subcellular localization [6, 7]; second, patients with HD present aggregated tau inclusions within various structures of the brain, including those with young‐onset [8, 9] and, third, the MAPT H2 haplotype influences the cognitive function of HD patients [9, 10].