POLD3 and frontotemporal dementia: Mitotic DNA synthesis, which is a mechanism used in the repair of under-replicated DNA by MUS81 and POLD3 [25], was rarely observed in FTD-treated mitotic cells, compared with aphidicolin-treated cells, even though FTD-induced the accumulation of under-replicated regions and ssDNA (Supplementary Fig. 1B and ref. [7]).