In comparison with one-half reduction of total NRXN3 expression in the AD cortex, the exon 22a-24b variant that encodes the major transmembrane isoform was expressed at levels that were decreased, by 85% in AD subjects with either CC or CC/TT genotypes (P < 0.0001 by two-tailed Mann-Whitney tests for both comparisons) (Fig. 4b). This evidence concerns the gene NRXN3 and Alzheimer disease.