Association of mu-opioid receptor variants and response to citalopram treatment in major depressive disorder.

OBJECTIVE: Because previous preclinical and clinical studies have implicated the endogenous opioid system in major depression and in the neurochemical action of antidepressants, the authors examined how DNA variation in the mu-opioid receptor gene may influence population variation in response to citalopram treatment. METHOD: A total of 1,953 individuals from the Sequenced Treatment Alternatives to Relieve Depression (STAR*D) study were treated with citalopram and genotyped for 53 single nucleotide polymorphisms (SNPs) in a 100-kb region of the OPRM1 gene. The sample consisted of Non-Hispanic Caucasians, Hispanic Caucasians, and African Americans. Population stratification was corrected using 119 ancestry informative markers and principal components analysis. Markers were tested for association with phenotypes for general and specific citalopram response as well as remission. RESULTS: Association between one SNP and specific citalopram response was observed. After Bonferroni correction, the strongest finding was the association between the rs540825 SNP and specific response. The rs540825 polymorphism is a nonsynonymous SNP in the final exon of the mu-opioid receptor-1X isoform of the OPRM1 gene, resulting in a histidine to glutamine change in the intracellular domain of the receptor. When Hispanic and Non-Hispanic Caucasians were analyzed separately, similar results in the population-corrected analyses were detected. CONCLUSIONS: These results suggest that rates of response to antidepressants and consequent remission from major depressive disorder are influenced by variation in the mu-opioid receptor gene as a result of either an effect on placebo response or true pharmacologic response.

A genomewide association study of citalopram response in major depressive disorder.

BACKGROUND: Antidepressant response is likely influenced by genetic constitution, but the actual genes involved have yet to be determined. We have carried out a genomewide association study to determine whether common DNA variation influences antidepressant response. METHODS: Our sample is derived from Level 1 participants in the Sequenced Treatment Alternatives to Relieve Depression (STAR*D) study, all treated with citalopram. Association for the response phenotype included 883 responders and 608 nonresponders. For the remission phenotype, 743 subjects that achieved remission were compared with 608 nonresponders. We used a subset of single nucleotide polymorphisms (SNPs; n = 430,198) from the Affymetrix 500K and 5.0 Human SNP Arrays, and association analysis was carried out after correcting for population stratification. RESULTS: We identified three SNPs associated with response with p values less than 1 x 10(-5) near the UBE3C gene (rs6966038, p = 4.65 x 10(-7)), another 100 kb away from BMP7 (rs6127921, p = 3.45 x 10(-6)), and a third that is intronic in the RORA gene (rs809736, p = 8.19 x 10(-6)). These same SNPs were also associated with remission. Thirty-nine additional SNPs are of interest with p values < or = .0001 for the response and remission phenotypes. CONCLUSIONS: Although the findings reported here do not meet a genomewide threshold for significance, the regions identified from this study provide targets for independent replication and novel pathways to investigate mechanisms of antidepressant response. This study was not placebo controlled, making it possible that we are also observing associations to nonspecific aspects of drug treatment of depression.

Resequencing of serotonin-related genes and association of tagging SNPs to citalopram response.

Several reports have been published investigating the relationship between common variants in serotonin-related candidate genes and antidepressant response, and most of the results have been equivocal. We previously reported a significant association between variants in serotonin-related genes and response to the selective serotonin reuptake inhibitor fluoxetine. Here, we attempt to expand upon and replicate these results by (i) resequencing the exonic and putatively regulatory regions of five serotonin-related candidate genes (HTR1A, HTR2A, TPH1, TPH2, and MAOA) in our fluoxetine-treated sample to uncover novel variants; (ii) selecting tagging single nucleotide polymorphisms (SNPs) for these genes from the resequencing data; and (iii) evaluating these tagging SNPs for association with response to the selective serotonin reuptake inhibitor citalopram in an independent sample of participants who are enrolled in the Sequenced Treatment Alternatives to Relieve Depression (STAR*D) clinical study (N=1953). None of the variants associated previously with fluoxetine response were found to be associated with citalopram response in the STAR*D sample set. Nor were any of the additional tagging SNPs found to be associated with citalopram response. An additional SNP in HTR2A (rs7997012), previously reported to be associated with outcome of citalopram treatment in this sample, but not well tagged by any of the other SNPs we studied, was also genotyped, and was associated with citalopram response (P=0.0002), strongly supporting the previous observation in the same STAR*D sample. Our results suggest that resequencing the serotonin-related genes did not identify any additional common SNPs that have not been identified previously. It appears that genetic variation in these five genes has a marginal effect on response to citalopram, although a previously observed association was supported and awaits replication in an independent sample.

Pharmacokinetic genes do not influence response or tolerance to citalopram in the STAR*D sample.

BACKGROUND: We sought to determine whether clinical response or tolerance to the Selective Serotonin Reuptake Inhibitor (SSRI) citalopram is associated with genetic polymorphisms in potentially relevant pharmacokinetic enzymes. METHODOLOGY: We used a two-stage case-control study design in which we split the sample of 1,953 subjects from the Sequenced Treatment Alternatives to Relieve Depression (STAR*D) trial into a discovery (n = 831) and validation set (n = 1,046). Fifteen polymorphisms from five (CYP2D6, ABCB1, CYP2C19, CYP3A4, and CYP3A5) pharmacokinetic genes were genotyped. We examined the associations between these polymorphisms and citalopram response and tolerance. Significant associations were validated in the second stage for those polymorphism found to be statistically significant in the first stage. CONCLUSIONS: No genetic polymorphism in the pharmacokinetic genes examined was significantly associated with our response or tolerance phenotypes in both stages. For managing pharmacological treatment with citalopram, routine screening of the common pharmacokinetic DNA variants that we examined appears to be of limited clinical utility.

Analysis of association between the serotonin transporter and antidepressant response in a large clinical sample.

BACKGROUND: SLC6A4 encodes the serotonin transporter, the protein primarily responsible for the termination of serotonin neurotransmission. Because many antidepressants inhibit the transporter, it has been the focus of intense pharmacogenetic analysis. We sought to replicate our previous findings that SLC6A4 is associated with response to a selective serotonin reuptake inhibitor (SSRI) in a large case-control study. METHODS: Genotypes at the SLC6A4 locus were obtained for 1,914 subjects in the Sequenced Treatment Alternatives to Relieve Depression (STAR*D) study and then tested for association to treatment response of the SSRI citalopram. RESULTS: Nine tagging single nucleotide polymorphisms and two variants previously associated with antidepressant response, including a promoter repeat polymorphism, were genotyped. Single marker and haplotypic analyses failed to detect association with antidepressant response in the largest clinical sample studied to date. CONCLUSIONS: The lack of association between response to an SSRI and variation at the SLC6A4 locus in this large sample, carefully characterized for response to citalopram, strongly suggests that SSRI response in major depression is not determined by DNA variation at this locus. These findings do not replicate findings of a number of studies with considerably smaller sample sizes. Other genetic determinants of SSRI response in depression should be sought.

Sequence analysis of the serotonin transporter and associations with antidepressant response.

BACKGROUND: The serotonin transporter is the molecular target of many antidepressants, and the gene (SLC6A4) encoding this protein has been associated with response to selective serotonin reuptake inhibitors (SSRIs). We sought to test further the hypothesis that SLC6A4 is associated with SSRI response by resequencing this gene in subjects with major depression. METHODS: The sequence of all exons, parts of all introns, and the promoter region containing a polymorphic repeat polymorphism (HTTLPR) previously associated with SSRI response was determined for 96 subjects, and variants were tested for association to treatment response with fluoxetine. RESULTS: We screened a total of 712 kilobases of sequence and found 27 SLC6A4 variants, 21 of which were previously undescribed. Seventeen were seen on one chromosome each, including three of the five exonic variants. One polymorphism (rs25531), just upstream of the HTTLPR, showed evidence of an association with treatment response, and biochemical experiments showed this polymorphism altered binding of nuclear extracts to a consensus sequence for the activator protein 2 transcription factor, which is believed to be a critical factor in regulating neural gene expression in mammals. CONCLUSIONS: These results support an association between response to SSRIs and deoxyribonucleic acid variation at the serotonin transporter locus. We have also identified a potentially important functional variant that contributes to this association and a possible biologic mechanism that could mediate its effect.