Compared with cognitively normal participants, the largest reductions in FA were within bilateral uncinate fasciculus (right: −7.2%/yr, 95% CI = −9.7 to −4.7%, p < 0.001; left: −7.9%/yr, 95% CI = −12.0 to −3.7%, p < 0.001) in MAPT mutation carriers; bilateral paracallosal cingulum bundle (right: −6.7%/yr, 95% CI = −10.0 to −3.4%, p < 0.001; left: −5.6%/yr, 95% CI = −8.3 to −2.8%, p < 0.001) in those with sporadic bvFTD, and in right paracallosal cingulum bundle (6.8%/yr, 95% CI = −11.3 to 2.2%, p = 0.004) in C9ORF72 mutation carriers. This evidence concerns the gene MAPT and behavioral variant of frontotemporal dementia.