Association of galanin haplotypes with alcoholism and anxiety in two ethnically distinct populations

Abstract

The neuropeptide galanin (GAL) is widely expressed in the central nervous system. Animal studies have implicated GAL in alcohol abuse and anxiety: chronic ethanol intake increases hypothalamic GAL mRNA; high levels of stress increase GAL release in the central amygdala. The coding sequence of the galanin gene, GAL, is highly conserved and a functional polymorphism has not yet been found. The aim of our study was, for the first time, to identify GAL haplotypes and investigate associations with alcoholism and anxiety. Seven single-nucleotide polymorphisms (SNPs) spanning GAL were genotyped in 65 controls from five populations: US and Finnish Caucasians, African Americans, Plains and Southwestern Indians. A single haplotype block with little evidence of historical recombination was observed for each population. Four tag SNPs were then genotyped in DSM-III-R lifetime alcoholics and nonalcoholics from two population isolates: 514 Finnish Caucasian men and 331 Plains Indian men and women. Tridimensional Personality Questionnaire harm avoidance (HA) scores, a dimensional measure of anxiety, were obtained. There was a haplotype association with alcoholism in both the Finnish (P=0.001) and Plains Indian (P=0.004) men. The SNPs were also significantly associated. Alcoholics were divided into high and low HA groups (>or= and <mean HA of population). In the Finns, haplotype (P<0.0001) and diplotype (P<0.0001) distributions differed between high HA alcoholics, low HA alcoholics and nonalcoholics. Our results from two independent populations suggest that GAL may contribute to vulnerability to alcoholism, perhaps mediated by dimensional anxiety.

Figure 1

GAL LD matrix in African-Americans (a); US Caucasians and Finnish Caucasians (b); and Plains Indians and Southwestern Indians (c). A schematic of the gene is given in the middle of each panel with lines indicating the positions of the seven SNPs. The eight exons are represented by rectangles. Each box represents D’, % linkage disequilibrium (LD) between SNP pairs, as generated by Haploview (Whitehead Institute for Biomedical Research, USA). Boxes without numbers represent complete LD; D’ = 100%. SNP IDs are public database rs numbers. *The tag SNPs for this gene region.

Figure 2

Differences in GAL haplotype frequencies between alcoholics and nonalcoholics. χ² comparisons across all four haplotypes: Finnish men, n=996, P < 0.001; Plains Indian men, n=263, P=0.045; and Plains Indian women, n=357, P=0.254.

Figure 3

GAL haplotype and diplotype frequencies in Finnish men: alcoholics with high harm avoidance (HA) ( > mean HA of nonalcoholics), alcoholics with low HA ( < mean HA of nonalcoholics) and nonalcoholics. χ² comparisons of the three groups across all four haplotypes: n=996, χ² = 37.2, 6 df, P < 0.0001; and all four diplotypes: n=452, χ² = 30.0, 6 df, P < 0.0001.

Figure 4

Conservation of GAL SNPs across five mammalian species (from top to bottom: human, chimp, mouse, rat, dog). Sequence alignment surrounding SNPs 1–7. The SNP numbers and positions are marked above the aligned sequences for five species. Dashed lines indicate that no sequence is available.