MAPT and semantic dementia: Approximately 40 pathogenic mutations in the MAPT gene have been identified, most of them are associated with clinical signs of FTDP-17 with degeneration in the frontotemporal lobar regions.[119] Tau mutations affecting splicing efficacy are located either in exon 10 or intron 10 and result in a change of the 4R/3R tau mRNA ratio.[120,121]