From 1997 to 2007: A decade journey through the H1 haplotype on 17q21 chromosome

The H1 haplotype was first identified 10 years ago. Initially, a dinucleotide polymorphism was detected in the tau (MAPT) gene and was subsequently found to be in linkage disequilibrium (LD) with other polymorphisms, forming the MAPT H1 haplotype, a risk factor for many neurological diseases, considered as tauopathies. Genetic and histopathologic data are in agreement that MAPT and its encoded protein have a pivotal role in the normal function of neurons. Currently, the H1 haplotype extends beyond the outer edges of MAPT encompassing multiple genes on chromosome 17 and thus increasing the number of candidate genes implicated in the pathogenesis of tauopathies. This review highlights the milestones and basic events in the journey towards uncovering the significance of the H1 haplotype.