MAPT and Alzheimer disease: hiPSC-based models have clearly shown impaired neurogenesis and abnormal dendritic and synaptic morphology [205,206], but most importantly have been used to link the two pathologies by showing that Down's syndrome cortical neurons secreted pathogenic Aβ peptide and their cell bodies and dendrites contained hyperphosphorylated Tau protein, a hallmark of AD neurons [45].