Two of the genes, CDH13 and GABRB1, have been associated with hypertension in a previous GWAS [6, 7, 15].
For two other interactions, GABRB1 and MAN1A1 and CHRNA7 and CDH13, a network of multiple genes instead of a single gene may establish the relationship between the two genes.
Thus, chromosome 4 contains a cluster comprising the genes GABRA2, GABRA4, GABRB1
, and GABRG1; chromosome 5 contains GABRA1, GABRA6, GABRB2, and GABRG2; and chromosome 15 contains GABRA5, GABRB3, and GABRG3 (see http:// www.ncbi.nhn.nih.gov/sites/ entrez?db=gene).
For example, genes called GABRA2, GABRA4, GABRB1
, and GABRG1 code for components of the GAB[A.sub.A] receptor, and a gene called GABAB2 codes for one component of the GAB[A.sub.B] receptor.