H1 haplotype identified 10 years ago from dinucleotide polymorphism in MAPT gene. H1 formed by linkage disequilibrium with other polymorphisms. H1 acts as risk factor for tauopathies. MAPT protein essential for neuron function per genetic and histopathologic data. H1 now spans beyond MAPT including multiple chromosome 17 genes as tauopathy candidates. Review covers milestones revealing H1 significance.