MAPT and dementia: Alzheimer's disease, the leading cause of dementia (World Health Organisation, 2020), is characterised by the pathological hallmarks of extracellular deposition of amyloid‐β (Aβ), intracellular accumulation of abnormally hyperphosphorylated tau into neurofibrillary tangles and brain atrophy due to neuronal and synapse loss (Blennow et al., 2006).