HTR1A and Alzheimer disease: Only two published GWASs have studied the association of genetic variants with the co-occurrence of AD and ND (or AD-ND codependence): one identified genome-wide significant SNPs that are located near MARK1 on chromosome 1, proximal to DDX6 on chromosome 11, or in the intronic region of KIAA1409 on chromosome 1439, and another, based exclusively on publicly-available data, found genome-wide significant association signals between IPO11 and HTR1A on chromosome 540.