Does pretreatment testing for serotonin transporter polymorphisms lead to earlier effects of drug treatment in patients with major depression? A decision-analytic model

Pharmacogenetics in the clinical analysis laboratory: clinical practice, research, and drug development pipeline

Introduction: Over the last decade, the spread of next-generation sequencing technology along with the rising cost in health management in national health systems has led to widespread use/abuse of pharmacogenetic tests (PGx) in the practice of many clinical disciplines. However, given their clinical significance, it is important to standardize these tests for having an interaction with the clinical analysis laboratory (CAL), in which a PGx service can meet these requirements. Areas covered: A diagnostic test must meet the criteria of reproducibility and validity for its utility in the clinical routine. This present review mainly describes the utility of introducing PGx tests in the CAL routine to produce correct results useful for setting up personalized drug treatments. Expert opinion: With a PGx service, CALs can provide the right tool to help clinicians to make better choices about different categories of drugs and their dosage and to manage the economic impact both in hospital-based settings and in National Health Services, throughout electronic health records. Advances in PGx also allow a new approach for pharmaceutical companies in order to improve drug development and clinical trials. As a result, CALs can achieve a powerful source of epidemiological, clinical, and research findings from PGx tests.

Pharmacogenomics in Psychiatric Practice

Pharmacogenomic testing in psychiatry is becoming an established clinical procedure. Several vendors provide clinical interpretation of combinatorial pharmacogenomic testing of gene variants that have documented predictive implications regarding either pharmacologic response or adverse effects in depression and other psychiatric conditions. Such gene profiles have demonstrated improvements in outcome in depression, and reduction of cost of care of patients with inadequate clinical response. Additionally, several new gene variants are being studied to predict specific response in individuals. Many of these genes have demonstrated a role in the pathophysiology of depression or specific depressive symptoms. This article reviews the current state-of-the-art application of psychiatric pharmacogenomics.

Genetic Testing for Psychopharmacology: Is It Ready for Prime Time?

Genetic testing in psychiatric practice may be a beneficial adjunct to the nursing toolbox of considerations used to improve patient outcomes. Since 2004, the psychiatric community has used genotyping to personalize medication options for their patients. Although not a definitive or exact science, pharmacogenetic testing for psychopharmacological treatment options offers nurses and their patients insights into potential treatments that will reduce the current trial-and-error prescribing practices and more quickly improve patients' quality of life. The current article guides nurses through the process of conducting genetic testing, interpreting the results, and applying the results in clinical practice using a fictitious case example. [Journal of Psychosocial Nursing and Mental Health Services, 55(3), 19-23.].

Genome-wide association studies in pharmacogenomics of antidepressants

Major depressive disorder (MDD) is one of the most common psychiatric disorders worldwide. Doctors must prescribe antidepressants based on educated guesses due to the fact that it is unmanageable to predict the effectiveness of any particular antidepressant in an individual patient. With the recent advent of scientific research, the genome-wide association study (GWAS) is extensively employed to analyze hundreds of thousands of single nucleotide polymorphisms by high-throughput genotyping technologies. In addition to the candidate-gene approach, the GWAS approach has recently been utilized to investigate the determinants of antidepressant response to therapy. In this study, we reviewed GWAS studies, their limitations and future directions with respect to the pharmacogenomics of antidepressants in MDD.

Serotonin pathway polymorphisms and the treatment of major depressive disorder and anxiety disorders

While antidepressants are widely used to treat major depressive disorder and anxiety disorders, only half of the patients will respond to antidepressant treatment and only a third of patients will experience a remission of symptoms. Identification of genetic biomarkers that predict antidepressant treatment response could thus greatly improve current clinical practice by providing guidance on which drug to use for which patient. Most antidepressant drugs for the treatment of depression and anxiety disorders have effects on the serotonergic neurotransmitter system; thus, genetic polymorphisms in the genes involved in this pathway represent logical candidates for investigation. This article reviews recent findings on the pharmacogenetics of antidepressant drugs with a focus on serotonergic pathway polymorphisms and discusses future clinical applications.

Clinical implications of genetic variation in the serotonin transporter promoter region: a review

OBJECTIVE

To determine the state of the art in understanding the role of genetic variation in the serotonin transporter (5-HTT) promoter region (5-HTTLPR) in the development of a depressive episode and in its response to treatment.

DATA SOURCES

PubMed and Ovid were used to search for articles published prior to December 2007 utilizing the key words serotonin transporter, 5-HTT, 5-HTTLPR, serotonin transporter gene, and SLC6A4.

STUDY SELECTION

All studies were reviewed, but case reports and small case series were excluded.

DATA EXTRACTION

All relevant articles were read by at least 2 of the coauthors and notes regarding study design, measures, data analysis, and findings were later used to construct the review.

DATA SYNTHESIS

A common genetic variant, the short allele, in which 44 base pairs are missing from the promoter of SLC6A4, is associated with a greater risk for developing a major depressive disorder in patients following exposure to adversity. This association appears to be most important in the early stages of the depressive disorder. Additionally, the likelihood of a positive response to antidepressant treatment may be reduced in these patients in terms of delayed response, greater adverse event load, or, in bipolar patients, mania induction and rapid cycling.

CONCLUSIONS

Selected genetic testing of patients with a recent history of significant adversity may be a reasonable tool that can enlighten treatment options and the course of illness. Ongoing work with the short allele of 5-HTT may also inform clinical guidelines of long-term treatment with antidepressants.

Pharmacogenetics of antidepressant drugs: current clinical practice and future directions

While antidepressants are widely used to treat mood and anxiety disorders, only half of the patients will respond to antidepressant treatment and only one-third of patients experience a full remission of symptoms. The identification of genetic biomarkers that predict antidepressant-treatment response can improve current clinical practice. This is an emerging field known as pharmacogenetics, which comprises of genetic studies on both the pharmacokinetics and pharmacodynamics of treatment response. Recent studies on antidepressant-treatment response have focused on both aspects of pharmacogenetics research, identifying new candidate genes that may predict better treatment response for patients. This paper reviews recent findings on the pharmacogenetics of antidepressant drugs and future clinical applications. Ultimately, these studies should lead to the use of genetic testing to guide the use of antidepressants in clinical practice.

Should pharmacogenetics be incorporated in major depression treatment? Economic evaluation in high- and middle-income European countries

The serotonin transporter 5-HTTLPR polymorphism moderates response to SSRIs and side-effect burden. The aim of this study is to quantify the cost-utility of incorporating 5-HTTLPR genotyping in drug treatment of major depressive disorder (MDD). We previously reported a theoretical model to simulate antidepressant treatment with citalopram or bupropion for 12 weeks. The drugs were alternatively selected according to an 'as usual' algorithm or based on response and tolerability predicted by 5-HTTLPR profile. Here we apply this model to conduct a cost-utility analysis in three European regions with high GDP (Euro A), middle GDP (Euro B) and middle-high GDP (Euro C). In addition we test a verification scenario in which citalopram+bupropion augmentation is administered to individuals with the least favorable 5-HTTLPR genotype. Treatment outcomes are remission and Quality Adjusted-Life Weeks (QALW). Cost data (international $, year 2009) are retrieved from the World Health Organization (WHO) and national official sources. In base-case scenario incremental cost-effectiveness ratio (ICER) values are $1147 (Euro A), $1185 (Euro B) and $1178 (Euro C). From cost-effectiveness acceptability curve (CEAC), the probability of having an ICER value below WHO recommended cost-utility threshold (3 GDP per capita=$1926) is >90% in high-income countries (Euro A). In middle- income regions, these probabilities are <30% (Euro B) and <55% (Euro C) respectively. All estimates are robust against variations in treatment parameters, but if genetic test cost decreases to $100, pharmacogenetic approach becomes cost-effective in middle-income countries (Euro B). This simulation using data from 27 European states suggests that choosing antidepressant treatment from the results of 5-HTTLPR might be a cost-effective solution in high income countries. Its feasibility in middle income countries needs further research.

A model to incorporate genetic testing (5-HTTLPR) in pharmacological treatment of major depressive disorders

OBJECTIVE

To evaluate the benefit of pharmacogenetics in antidepressant treatment.

METHODS

In a simulated trial 100,000 subjects in a current episode of major depressive disorder (MDD) received citalopram or bupropion based on the clinician's decision (algorithm A) or following indications from 5-HTTLPR genetic testing (algorithm B), which effect size of was estimated from a meta-analysis of pharmacogenetic trials. A and B were compared in a cost-utility analysis (12 weeks). Costs (international $, 2010) were drawn from official sources. Treatment effects were expressed as quality-adjusted life weeks (QALWs). Outcome was incremental cost-effectiveness ratio (ICER).

RESULTS

Under base-case conditions, genetic test use was associated with increases in antidepressant response (0.062 QALWs) and tolerability (0.016 QALWs) but cost benefit was not acceptable (ICER = $2,890; $1,800-$4,091). However, when the joint effect on antidepressant response and tolerability was analyzed in two recurrent episodes, ICER dropped to $1,392 ($837-$1,982). Cost-effectiveness acceptability curve (CEAC) showed a >80% probability that ICER value fell below the commonly accepted 3 times Gross Domestic Product (GDP) threshold (World Health Organization) and therefore suggesting cost-effectiveness.

CONCLUSION

Notwithstanding some caveats (exclusion of gene-gene and gene-environment interactions; simple 5-HTTLPR architecture), this simulation is favourable to incorporate pharmacogenetic test in antidepressant treatment.

Serotonin transporter gene polymorphisms and treatment-resistant depression

Major Depression Disorder (MDD) is a serious mental illness that is one of the most disabling diseases worldwide. In addition, approximately 15% of depression patients are defined treatment-resistant (TRD). Preclinical and genetic studies show that serotonin modulation dysfunction exists in patients with TRD. Some polymorphisms in the promoter region of the serotonin transporter gene (SLC6A4) are likely to be involved in the pathogenesis/treatment of MDD; however, no data are available concerning TRD. Therefore, in order to investigate the possible influence of SLC6A4 polymorphisms on the risk of TRD, we genotyped 310 DSM-IV MDD treatment-resistant patients and 284 healthy volunteers. We analysed the most studied polymorphism 5-HTTLPR (L/S) and a single nucleotide substitution, rs25531 (A/G), in relation to different functional haplotype combinations. However the correct mapping of rs25531 is still debated whether it is within or outside the insertion. Our sequencing analysis showed that rs25531 is immediately outside of the 5-HTTLPR segment. Differences in 5-HTTLPR allele (p=0.04) and in L allele carriers (p<0.05) were observed between the two groups. Concerning the estimated haplotype analyses, L(A)L(A) homozygote haplotype was more represented among the control subjects (p=0.01, OR=0.64 95%CI: 0.45-0.91). In conclusion, this study reports a protective effect of the L(A)L(A) haplotype on TRD, supporting the hypothesis that lower serotonin transporter transcription alleles are correlated to a common resistant depression mechanism.

Review and meta-analysis of antidepressant pharmacogenetic findings in major depressive disorder

This systematic review summarizes pharmacogenetic studies on antidepressant response and side effects. Out of the 17 genes we reviewed, 8 genes were entered into the meta-analysis (SLC6A4, HTR1A, HTR2A, TPH1, gene encoding the beta-3 subunit, brain-derived neurotrophic factor (BDNF), HTR3A and HTR3B). TPH1 218C/C genotype (7 studies, 754 subjects) was significantly associated with a better response (odds ratio, OR=1.62; P=0.005) with no heterogeneity between ethnicities. A better response was also observed in subjects with the Met variant within the BDNF 66Val/Met polymorphism (4 studies, 490 subjects; OR=1.63, P=0.02). Variable number of tandem repeats polymorphism within intron 2 (STin2) 12/12 genotype showed a trend toward a better response in Asians (STin2: 5 studies, 686 subjects; OR=3.89, P=0.03). As for side effects, pooled ORs of serotonin transporter gene promoter polymorphism (5-HTTLPR) l (9 studies, 2642 subjects) and HTR2A -1438G/G (7 studies, 801 subjects) were associated with a significant risk modulation (OR=0.64, P=0.0005) and (OR=1.91, P=0.0006), respectively. Interestingly, this significance became more robust when analyzed with side effect induced by selective serotonin reuptake inhibitors only (5-HTTLPR: P=0.0001, HTR2A: P<0.0001). No significant result could be observed for the other variants. These results were not corrected for multiple testing in each variant, phenotype and subcategory. This would have required a Bonferroni significance level of P<0.0023. Although some heterogeneity was present across studies, our finding suggests that 5-HTTLPR, STin2, HTR1A, HTR2A, TPH1 and BDNF may modulate antidepressant response.

Both synthesis and reuptake are critical for replenishing the releasable serotonin pool in Drosophila

The two main sources of serotonin available for release are expected to be newly synthesized serotonin and serotonin recycled after reuptake by the serotonin transporter. However, their relative importance for maintaining release and the time course of regulation are unknown. We studied serotonin signaling in the ventral nerve cord of the larval Drosophila CNS. Fast-scan cyclic voltammetry at implanted microelectrodes was used to detect serotonin elicited by channelrhodopsin2-mediated depolarization. The effects of reuptake were probed by incubating in cocaine, which is selective for the serotonin transporter in Drosophila. p-chlorophenylalanine, an inhibitor of tryptophan hydroxylase2, was used to investigate the effects of synthesis. Stimulations were repeated at various intervals to assess the time course of recovery of the releasable pool. Reuptake is important for the rapid replenishment of the releasable pool, on the 1 min time scale. Synthesis is critical to the longer-term replenishment (10 min) of the releasable pool, especially when reuptake is also inhibited. Concurrent synthesis and reuptake inhibition decreased both serotonin tissue content measured by immunohistochemistry (by 50%) and the initial amount of evoked serotonin (by 65%). Decreases in evoked serotonin are rescued by inhibiting action potential propagation with tetrodotoxin, implicating endogenous activity in the depletion. These results show synthesis is necessary to replenish part of the releasable serotonin pool that is depleted after reuptake inhibition, suggesting that regulation of synthesis may modulate the effects of serotonin reuptake inhibitors.

Application of pharmacogenomics to clinical problems in depression

The goal of this article is to review the literature for evidence supporting an association between polymorphisms within drug target genes and clinical outcomes for treating depression, with a purpose to identify a research area having the most promising potential to be introduced into clinical settings, and thus, discussing the perspectives of genotyping in antidepressant therapy. A total of 67 articles were identified. Polymorphic sites within the serotonin transporter gene promoter, 5-HTTLPR, were the most studied polymorphisms. All except three articles were designed as cohort studies. The other three articles included two meta-analyses and one decision-analytic model. The main finding from these meta-analyses was that the l variant was associated with a better response to selective serotonin reuptake inhibitors. The main conclusion from the decision-analytic model study was that performing genetic testing before prescribing antidepressant treatment may lead to greater numbers of patients experiencing remission early in treatment. Clinical outcomes of genotyping this polymorphism were evaluated by improvement of depression score, odds ratio and absolute risk reduction.

Pharmacogenomics with antidepressants in the STAR*D study

Major depressive disorder is one of the most common psychiatric disorders worldwide. No single antidepressant has been shown to be more effective than any other in lifting depression, and the effectiveness of any particular antidepressant in an individual is difficult to predict; therefore, doctors must prescribe antidepressants based on educated guesses. SNPs can be used in clinical association studies to determine the contribution of genes to drug efficacy. Evidence is accumulating to suggest that the efficacy of antidepressants results from the combined effects of a number of genetic variants, such as SNPs. Although there are not enough data currently available to prove this hypothesis, an increasing number of genetic variants associated with antidepressant response are being discovered. In this article, we review the pharmacogenomics of the drug efficacy of antidepressants in major depressive disorder. First, we survey the SNPs and genes identified as genetic markers that are correlated and associated with the drug efficacy of antidepressants in the Sequenced Treatment Alternatives for Depression (STAR*D) study. Second, we investigate candidate genes that have been suggested as contributing to treatment-emergent suicidal ideation during the course of antidepressant treatment in the STAR*D study. Third, we briefly describe the pharmacokinetic genes examined in the STAR*D study, and finally, we summarize the limitations with respect to the pharmacogenomics studies in the STAR*D study. Future research with independent replication in large sample sizes is needed to confirm the role of the candidate genes identified in the STAR*D study in antidepressant treatment response.

[The genetics of depressive disorders]

Among the most common severe psychiatric disorders worldwide, depressive disorders are a leading cause of morbidity, the onset usually occurring during childhood or adolescence. Symptomatology, prevalence, outcome and treatment differentiate depressive disorder nosologically as being either unipolar depression or bipolar disorder, which is characterized by one or more episodes of mania with or without episodes of depression. Genetic factors decisively influence the susceptibility to depressive disorders. Family studies and twin studies have been essential in defining the magnitude of familial risk and liability to heritability, particularly in the case of bipolar disorder. In recent years, linkage and association studies have made great strides towards identifying candidate genes. Particularly the s-allele of the serotonin transporter has been repeatedly confirmed to be a risk factor. Meta-analyses suggest, however, that the genetic contributions of the ascertained loci are relatively small. Along with genetic factors, environmental factors are heavily involved. Gene-environment action plays a pivotal role, particularly in unipolar depression. The genetic disposition seems to be modulated by a protective or pathogenic environment. Early-onset disorders must be further investigated in future as studies to date are somewhat limited.