NRXN3 and Alzheimer disease: Since the NRXN3 haplotype tagged by rs8019381 (Fig. 3a) has been associated with altered patterns of expression of NRXN3 splice variants that encode transmembrane vs soluble isoforms, we evaluated the distributions of these isoforms in control brains, which were virtually all from individuals with CC haplotypes, and in frontal cortex samples of AD brains from CC, CT, and TT individuals.