Eric J. Peters

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.

Investigation of serotonin-related genes in antidepressant response

In this study, we sought out to test the hypothesis that genetic factors may influence antidepressant response to fluoxetine. The investigation focused on seven candidate genes in the serotonergic pathway involved in the synthesis, transport, recognition, and degradation of serotonin. Our clinical sample consisted of 96 subjects with unipolar major depression treated with fluoxetine with response variables assessed after a 12-week trial. Patient data were also collected to investigate the pattern of drug response. Using a high-throughput single-nucleotide polymorphism (SNP) genotyping platform and capillary electrophoresis, we genotyped patients at 110 SNPs and four repeat polymorphisms located in seven candidate genes (HTR1A, HTR2A, HTR2C, MAOA, SLC6A4, TPH1, and TPH2). Statistical tests performed included single-locus and haplotype association tests, and linkage disequilibrium (LD) estimation. Little evidence of population stratification was observed in the sample with 20 random SNPs using a genomic control procedure. Our most intriguing result involved three SNPs in the TPH1 gene and one SNP in the SLC6A4 gene, which show significant single-locus association when response to fluoxetine is compared to nonresponse (P=0.02–0.04). All odds ratios indicated an increased risk of not responding to fluoxetine. In the specific response vs nonspecific and nonresponse comparison, three SNPs in the TPH2 gene (P=0.02–0.04) were positively associated and one SNP in the HTR2A gene (P=0.02) was negatively associated. When comparing specific response to nonspecific response, we found significant negative associations in three SNPs in the HTR2A gene (P=0.001–0.03) and two SNPs in the MAOA gene (P=0.03–0.05). We observed variable, although strong LD, in each gene and unexpectedly low numbers of estimated haplotypes, formed from tagged SNPs. Significant haplotype associations were found in all but the HTR1A and HTR2C genes. Although these data should be interpreted cautiously due to the small sample size, these results implicate TPH1 and SLC6A4 in general response, and HTR2A, TPH2, and MAOA in the specificity of response to fluoxetine. Intriguingly, we observe that a number of the less frequent alleles of many of the SNP markers were associated with the nonresponse and nonspecific phenotypes.

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.

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.

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.

Response to Zhang et al. (2005) loss-of-function mutation in tryptophan hydroxylase-2 identified in unipolar major depression. Neuron 45, 11-16 [2] (multiple letters)

Zhang et al. reported a naturally occurring Arg441His missense variant of the human tryptophan hydroxylase-2 (TPH2) gene. The His441 allele was reported to be more abundant in a cohort of 87 depressed patients compared to 219 controls (Zhang et al., 2005). The frequency of His441 was higher in the depressed patients (0.06), among whom there were two His/His homozygotes and seven heterozygotes. His441 was also observed among the 219 controls (allele frequency 0.009), among whom one His/His homozygote and two Arg/His heterozygotes were detected. This reported association with depression is of note in the context of the effect of this substitution in reducing serotonin synthesis by approximately 80% in a heterologous expression assay in a rat cell line (Zhang et al., 2005) and through the observation of the role of TPH2 variants as genetic predictors of depression (Zill et al., 2004) and response to antidepressants (Peters et al., 2004). The authors of this letter represent three independent groups of investigators who have resequenced the relevant region of TPH2 in some 779 unrelated individuals (Table 1), including 403 with major depression (ages 19–74, n = 21 > 60 years). In addition, another 1740 individuals with major depression (from the STAR*D study, ages 18–75, n = 121 > 60 years) were genotyped (Table 1). The sequenced and genotyped individuals represent five ethnic populations. Psychiatric assessment was accomplished using semistructured psychiatric interviews: NIAAA, SCID or SADS-L; NIMH and UCSF, SCID-I/P. Major depression was diagnosed by DSMIII-R or DSM-IV criteria, and a DSM-IV checklist was used for the STAR*D samples. Additional descriptions of individual data sets have been reported (Nielsen et al., 1998; Robin et al., 1997; Roy, 2003; Peters et al., 2004; Rush et al., 2004). All data were collected following informed consent and under human research protocols approved by IRBs of the respective institutions. For direct sequencing, genomic DNA was amplified by PCR with primers encompassing the Arg441His variant, sequenced using the BigDye Terminator V3.1 (Applied Biosystems Inc., Foster City, CA) and analyzed on ABI 3100 or 3730 sequencers. For genotyping, assays were performed using 50-nuclease assay (TaqMan, ID # PMT06-55) and analyzed on an LJL plate reader (Molecular Devices, Sunnyvale, CA). 20% of the

Variants in PDE11A and PDE1A are not associated with citalopram response

Recently, Wong et al.1 investigated an association between polymorphisms in phosphodiesterase (PDE) genes and antidepressant response in a Mexican-American population. Two single nucleotide polymorphisms (SNPs) were associated with remission in response to either fluoxetine or desipramine although sample sizes for remitter and nonremitter groups were of limited size. Association between the reported PDE gene SNPs and remission in response to antidepressants requires further investigation using larger sample sizes. We sought to replicate the response phenotype data for two SNPs, rs1549870 (PDE1A) and rs1880916 (PDE11A) in a similar ethnic group for the nonremitter vs remitter analysis in the Wong et al. study. Additionally, we examined this potential association in Non-Hispanic Caucasians and African-American samples.

The ABCB1 transporter gene and antidepressant response.

P-glycoprotein, encoded by the ABCB1 gene, may modulate the brain concentration of several antidepressants. Functional genetic variation is thought to exist in this gene, and here we review several studies that have attempted to associate this variation with clinical response to antidepressant treatment.