MAPT and frontotemporal dementia: As stated earlier, 3R tau predominates in development, whereas levels of 4R tau increase during early life, with 4R tau levels matching 3R in adulthood.82,95 However, the developmental regulation of tau splicing is known to be dysregulated in neurons derived from FTD patients with the 10 + 16 mutation in MAPT,96 a splice site mutation that destabilizes tau RNA and leads to a 2–6-fold increase in the inclusion of exon 10, the exon responsible for production of the 4R isoform97