BDNF and Alzheimer disease: The T/T homozygous of the BDNF C270T polymorphism were absent in all groups; the T/C carriers showed increased circulating BDNF, particularly in the MCI group (p = 0.021 between C/C and C/T carriers in MCI, and p = 0.036 between AD and MCI, Figure 1d, Table 2).