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Sunday, August 4, 2013

Rare SERINC2 variants are specific for alcohol dependence in individuals of European descent.


We have previously reported a top-ranked risk gene [i.e., serine incorporator 2 gene (SERINC2)] for alcohol dependence in individuals of European descent by analyzing the common variants in a genome-wide association study. In the present study, we comprehensively examined the rare variants [minor allele frequency ] in the NKAIN1-SERINC2 region to confirm our previous finding.

A discovery sample (1409 European-American patients with alcohol dependence and 1518 European-American controls) and a replication sample (6438 European-Australian family participants with 1645 alcohol-dependent probands) were subjected to an association analysis. A total of 39 903 individuals from 19 other cohorts with 11 different neuropsychiatric and neurological disorders served as contrast groups. The entire NKAIN1-SERINC2 region was imputed in all cohorts using the same reference panels of genotypes that included rare variants from the whole-genome sequencing data. We stringently cleaned the phenotype and genotype data, and obtained a total of about 220 single-nucleotide polymorphisms in individuals of European descent and about 450 single-nucleotide polymorphisms in the individuals of African descent.

Using a weighted regression analysis implemented in the program SCORE-Seq, we found a rare variant constellation across the entire NKAIN1-SERINC2 region that was associated with alcohol dependence in European-Americans and European-Australians), but not in African-Americans, and not associated with any other disorder examined. Association signals in this region came mainly from SERINC2, a gene that codes for an activity-regulated protein expressed in the brain that incorporates serine into lipids. In addition, 26 individual rare variants were nominally associated with alcohol dependence in European-Americans . The associations of five of these rare variants that lay within SERINC2 showed region-wide significance and 25 associations survived correction for a false discovery rate . The associations of two rare variants at SERINC2 were replicated in European-Australians .

We concluded that SERINC2 was a replicable and significant risk gene specific for alcohol dependence in individuals of European descent.


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