masks was calculated using in-house software programmed in IDL (http://www.creaso.com). Statistical analysis: Analysis of covariance (ANCOVA) was performed for left and right total hippocampal GM volume and each three subregions with two-level factors group (patients, controls), genotype (rs1545843 AA vs. AG/GG, equally for rs1081681), and gender, covarying for age, squared age, total GM volume and sequence type. Levene’s tests for equality of error variances was explored and found non-significant for all tests (fig. S4). P-values were compared with a Bonferroni-corrected threshold to adjust for 18 tests (2 SNPs, 9 volumetric measurements [including motor cortex as control region]: 0.05/18=0.0028). Both nominal and corrected p-values are indicated in fig. 5 and tab. S2.
