Methods: We analysed nuclear tau epitopes (Tau-1, AT8, PHF1, T181, and S262) by indirect immunofluorescence in SK-N-BE neuroblastoma cells under proliferative and retinoic acid-induced differentiated conditions and in post-mortem hippocampal CA1 neurons from foetal, young, aged, and AD brains. The gene discussed is PHF1; the disease is Alzheimer disease.