MAPT and hippocampal atrophy: Hippocampal atrophy is a marker of AD pathology, as hippocampal volume has been shown to negatively associate with the tau and amyloid beta burden in AD (Apostolova et al.,2015) and hippocampal atrophy can predate a diagnosis of dementia by a period of up to several years (Tondelli et al.,2012; de Flores et al.,2015) also making it a potentially important prodromal biomarker.