MAPT and Parkinson disease: Reasons for studying the relationship between H1 haplotype and PD were i) the proven increased transcriptional activity of H1 compared to H2,[20] suggesting a possible mechanism of PD susceptibility, since overexpression of transgenic tau has been found to cause neuronal death in Drosophila without neurofibrillary tangles,[40] and ii) a possible link between elevated H1 percentages among PD patients and tau mediated α-synuclein fibrillization,[6] which is believed to play an important role in the development and progression of PD.