Objective: Depression and alcohol dependence (AD) are common psychiatric disorders that often co-occur. Both disorders are genetically influenced, with heritability estimates in the range of 35–60%. In addition, evidence from twin studies suggests that AD and depression are genetically correlated. Herein, we report results from a genome-wide association study of a comorbid phenotype, in which cases meet the Diagnostic and Statistical Manual of Mental Disorders-IV symptom threshold for major depressive symptomatology and the Diagnostic and Statistical Manual of Mental Disorders-IV criteria for AD.
Methods: Samples (N=467 cases and N=407 controls) were of European-American descent and were genotyped using the Illumina Human 1M BeadChip array.
Results: Although no single-nucleotide polymorphism (SNP) meets genome-wide significance criteria, we identified 10 markers with P values less than 1×10−5, seven of which are located in known genes, which have not been previously implicated in either disorder. Genes harboring SNPs yielding P values less than 1×10−3 are functionally enriched for a number of gene ontology categories, notably several related to glutamatergic function. Investigation of expression localization using online resources suggests that these genes are expressed across a variety of tissues, including behaviorally relevant brain regions. Genes that have been previously associated with depression, AD, or other addiction-related phenotypes – such as CDH13, CSMD2, GRID1, and HTR1B – were implicated by nominally significant SNPs. Finally, the degree of overlap of significant SNPs between a comorbid phenotype and an AD-only phenotype is modest.
Conclusion: These results underscore the complex genomic influences on psychiatric phenotypes and suggest that a comorbid phenotype is partially influenced by genetic variants that do not affect AD alone.
aVirginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, Virginia
bWashington University School of Medicine, St. Louis, Missouri
cIndiana University School of Medicine, Indianapolis, Indiana
dUniversity of Connecticut, Farmington, Connecticut
eUniversity of Iowa, Iowa City, Iowa
fUniversity of California, San Diego, California
gSUNY Downstate Medical Center, Brooklyn, New York, USA
hAnkara University, Ankara, Turkey
All supplementary digital content is available directly from the corresponding author.
Correspondence to Dr Alexis C. Edwards, PhD, Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth PO Box 980126, Richmond, VA, 23298-0126, USATel: +1 804 828 8591; fax: +1 804 828 1471; e-mail: firstname.lastname@example.org; email@example.com
Received November 16, 2010
Accepted June 22, 2011