Pharmacogenetics of lithium prophylaxis in mood disorders: analysis of COMT, MAO-A, and Gbeta3 variants

Genetic and Epigenetic Markers of Lithium Response

The mood stabilizer lithium represents a cornerstone in the long term treatment of bipolar disorder (BD), although with substantial interindividual variability in clinical response. This variability appears to be modulated by genetics, which has been significantly investigated in the last two decades with some promising findings. In addition, recently, the interest in the role of epigenetics has grown significantly, since the exploration of these mechanisms might allow the elucidation of the gene–environment interactions and explanation of missing heritability. In this article, we provide an overview of the most relevant findings regarding the pharmacogenomics and pharmacoepigenomics of lithium response in BD. We describe the most replicated findings among candidate gene studies, results from genome-wide association studies (GWAS) as well as post-GWAS approaches supporting an association between high genetic load for schizophrenia, major depressive disorder or attention deficit/hyperactivity disorder and poor lithium response. Next, we describe results from studies investigating epigenetic mechanisms, such as changes in methylation or noncoding RNA levels, which play a relevant role as regulators of gene expression. Finally, we discuss challenges related to the search for the molecular determinants of lithium response and potential future research directions to pave the path towards a biomarker guided approach in lithium treatment.

The Repertoire of Small-Molecule PET Probes for Neuroinflammation Imaging: Challenges and Opportunities beyond TSPO

Neuroinflammation is an adaptive response of the central nervous system to diverse potentially injurious stimuli, which is closely associated with neurodegeneration and typically characterized by activation of microglia and astrocytes. As a noninvasive and translational molecular imaging tool, positron emission tomography (PET) could provide a better understanding of neuroinflammation and its role in neurodegenerative diseases. Ligands to translator protein (TSPO), a putative marker of neuroinflammation, have been the most commonly studied in this context, but they suffer from serious limitations. Herein we present a repertoire of different structural chemotypes and novel PET ligand design for classical and emerging neuroinflammatory targets beyond TSPO. We believe that this Perspective will support multidisciplinary collaborations in academic and industrial institutions working on neuroinflammation and facilitate the progress of neuroinflammation PET probe development for clinical use.

Twenty years of Lithium pharmacogenetics: A systematic review

Lithium is among the best proven treatments for patients diagnosed with Bipolar Disorder, however response to Lithium appears to be considerably variable among individuals and it has been suggested that this inconstancy in Lithium response could be genetically determined. Starting from this perspective, in the last few decades, a number of pharmacogenetic studies have attempted to identify genetic variants, which might be associated with response to Lithium in bipolar patients, in order to develop a pharmacogenetics test to tailor treatment on patients, identifying who will benefit the most from therapy with Lithium. Within this context, authors have critically reviewed pharmacogenetic studies of Lithium response in bipolar disorder, suggesting strategies for future work in this field. Computerized searches of PubMed and Embase databases, for studies published between 1998 and January 2018, was performed: 1162 studies were identified but only 37 relevant papers were selected for detailed review. Despite some interesting preliminary findings, the pharmacogenetics of Lithium and the development of a specific pharmacogenetics test in bipolar disorder appears to be a field still in its infancy, even though the advent of genome-wide association studies holds particular promise for future studies, which should include larger samples.

The Role of Pharmacogenomics in Bipolar Disorder: Moving Towards Precision Medicine

Bipolar disorder (BD) is a common and disabling psychiatric condition with a severe socioeconomic impact. BD is treated with mood stabilizers, among which lithium represents the first-line treatment. Lithium alone or in combination is effective in 60% of chronically treated patients, but response remains heterogenous and a large number of patients require a change in therapy after several weeks or months. Many studies have so far tried to identify molecular and genetic markers that could help us to predict response to mood stabilizers or the risk for adverse drug reactions. Pharmacogenetic studies in BD have been for the most part focused on lithium, but the complexity and variability of the response phenotype, together with the unclear mechanism of action of lithium, limited the power of these studies to identify robust biomarkers. Recent pharmacogenomic studies on lithium response have provided promising findings, suggesting that the integration of genome-wide investigations with deep phenotyping, in silico analyses and machine learning could lead us closer to personalized treatments for BD. Nevertheless, to date none of the genes suggested by pharmacogenetic studies on mood stabilizers have been included in any of the genetic tests approved by the Food and Drug Administration (FDA) for drug efficacy. On the other hand, genetic information has been included in drug labels to test for the safety of carbamazepine and valproate. In this review, we will outline available studies investigating the pharmacogenetics and pharmacogenomics of lithium and other mood stabilizers, with a specific focus on the limitations of these studies and potential strategies to overcome them. We will also discuss FDA-approved pharmacogenetic tests for treatments commonly used in the management of BD.

Pharmacogenomic aspects of bipolar disorder: An update

The hopes for readily implementable precision medicine are high. For many complex disorders, such as bipolar disorder, these hopes critically hinge on tangible successes in pharmacogenetics of treatment response or susceptibility to adverse events. In this article, we review the current state of pharmacogenomics of bipolar disorder including latest results from candidate genes and genome-wide association studies. The majority of studies focus on response to lithium treatment. Although a host of genes has been studied, hardly any replicated findings have emerged so far. Very small samples sizes and heterogeneous phenotype definition may be considered the major impediments to success in this field. Drawing from current experiences and successes in studies on diagnostic psychiatric phenotypes, we suggest several approaches for our way forward.

The C825T Polymorphism of the G-Protein β3 Gene as a Risk Factor for Depression: A Meta-Analysis

Background

TheG-protein β3 gene (GNβ3) has been implicated in psychiatric illness through its effects upon intracellular transduction of several neurotransmitter receptors. Multiple studies have investigated the relationship of the C825T polymorphism of the GNβ3 gene (GNβ3 C825T) to depression and antidepressant response. However, the relationship between GNβ3 C825T and depression remains inconsistent. Therefore, here we performed a meta-analysis to investigate the role of GNβ3 C825Tin depression risk.

Methods

Published case-control studies examining the association between GNβ3 C825T and depression were systematically searched for through several electronic databases (PubMed, Scopus, Science Direct, Springer, Embase, psyINFO, and CNKI). The association between GNβ3 C825T and depression risk were assessed by odd ratios (ORs) and their 95% confidence intervals (CIs) for each study. Pooled ORs were constructed for allele contrast (C versus T), homozygote (CC versus TT) model, heterozygote (CC versus CT) model, dominant model (CC + CT versus TT), and recessive (CC versus TT+CT) model. In order to evaluate possible biases, a sensitivity analysis was conducted by sequential deletion of individual studies in an attempt to assess the contribution of each individual dataset to the pooled OR.

Results

Nine studies, including 1055 depressed patients and 1325 healthy controls, were included. A significant association between GNβ3 C825Tand depression was found to exist, suggesting that the T-allele of GNβ3 C825Tcan increase susceptibility to depression. After stratification by ethnicity, the same association was found in the Asian subpopulation, but not the Caucasian subpopulation.

Conclusions

This is the first meta-analysis to reveal a relationship between GNβ3 C825T and depression. Asian T-allele carriers of GNβ3 C825T appear to be more susceptible to depression.

Molecular actions and clinical pharmacogenetics of lithium therapy

Mood disorders, including bipolar disorder and depression, are relatively common human diseases for which pharmacological treatment options are often not optimal. Among existing pharmacological agents and mood stabilizers used for the treatment of mood disorders, lithium has a unique clinical profile. Lithium has efficacy in the treatment of bipolar disorder generally, and in particular mania, while also being useful in the adjunct treatment of refractory depression. In addition to antimanic and adjunct antidepressant efficacy, lithium is also proven effective in the reduction of suicide and suicidal behaviors. However, only a subset of patients manifests beneficial responses to lithium therapy and the underlying genetic factors of response are not exactly known. Here we discuss preclinical research suggesting mechanisms likely to underlie lithium's therapeutic actions including direct targets inositol monophosphatase and glycogen synthase kinase-3 (GSK-3) among others, as well as indirect actions including modulation of neurotrophic and neurotransmitter systems and circadian function. We follow with a discussion of current knowledge related to the pharmacogenetic underpinnings of effective lithium therapy in patients within this context. Progress in elucidation of genetic factors that may be involved in human response to lithium pharmacology has been slow, and there is still limited conclusive evidence for the role of a particular genetic factor. However, the development of new approaches such as genome-wide association studies (GWAS), and increased use of genetic testing and improved identification of mood disorder patients sub-groups will lead to improved elucidation of relevant genetic factors in the future.

Pharmacogenomics of bipolar disorder

Bipolar disorder (BD) is a lifelong severe psychiatric condition with high morbidity, disability and excess mortality. The longitudinal clinical trajectory of BD is significantly modified by pharmacological treatment(s), both in acute and in long-term stages. However, a large proportion of BD patients have inadequate response to pharmacological treatments. Pharmacogenomic research may lead to the identification of molecular predictors of treatment response. When integrated with clinical information, pharmacogenomic findings may be used in the future to determine the probability of response/nonresponse to treatment on an individual basis. Here we present a selective review of pharmacogenomic findings in BD. In light of the evidence suggesting a genetic effect of lithium reponse in BD, we focused particularly on the pharmacogenomic literature relevant to this trait. The article contributes a detailed overview of the current status of pharmacogenomics in BD and offers a perspective on the challenges that can hinder its transition to personalized healthcare.

Genetic influences on response to mood stabilizers in bipolar disorder: current status of knowledge

Mood stabilizers form a cornerstone in the long-term treatment of bipolar disorder. The first representative of their family was lithium, still considered a prototype drug for the prevention of manic and depressive recurrences in bipolar disorder. Along with carbamazepine and valproates, lithium belongs to the first generation of mood stabilizers, which appeared in psychiatric treatment in the 1960s. Atypical antipsychotics with mood-stabilizing properties and lamotrigine, which were introduced in the mid-1990 s, form the second generation of such drugs. The response of patients with bipolar disorder to mood stabilizers has different levels of magnitude. About one-third of lithium-treated patients are excellent responders, showing total prevention of the episodes, and these patients are clinically characterized by an episodic clinical course, complete remission, a bipolar family history, low psychiatric co-morbidity and a hyperthymic temperament. It has been suggested that responders to carbamazepine or lamotrigine may differ clinically from responders to lithium. The main phenotype of the response to mood stabilizers is a degree of prevention against recurrences of manic and depressive episodes during long-term treatment. The most specific scale in this respect is the so-called Alda scale, where retrospective assessment of lithium response is scored on a 0-10 scale. The vast majority of data on genetic influences on the response to mood stabilizers has been gathered in relation to lithium. The studies on the mechanisms of action of lithium and on the neurobiology of bipolar disorder have led to the identification of a number of candidate genes. The genes studied for their association with lithium response have been those connected with neurotransmitters (serotonin, dopamine and glutamate), second messengers (phosphatidyl inositol [PI], cyclic adenosine-monophosphate [cAMP] and protein kinase C [PKC] pathways), substances involved in neuroprotection (brain-derived neurotrophic factor [BDNF] and glycogen synthase kinase 3-β [GSK-3β]) and a number of other miscellaneous genes. There are no published pharmacogenomic studies of mood stabilizers other than lithium, except for one study of the X-box binding protein 1 (XBP1) gene in relation to the efficacy of valproate. In recent years, a number of genome-wide association studies (GWAS) in bipolar disorders have been performed and some of those have also focused on lithium response. They suggest roles for the glutamatergic receptor AMPA (GRIA2) gene and the amiloride-sensitive cation channel 1 neuronal (ACCN1) gene in long-term lithium response. A promise for better elucidating the genetics of lithium response has been created by the formation of the Consortium on Lithium Genetics (ConLiGen) to establish the largest sample, to date, for the GWAS of lithium response in bipolar disorder. The sample currently comprises more than 1,200 patients, characterized by their response to lithium treatment according to the Alda scale. Preliminary results from this international study suggest a possible involvement of the sodium bicarbonate transporter (SLC4A10) gene in lithium response. It is concluded that the pharmacogenetics of response to mood stabilizers has recently become a growing field of research, especially so far as the pharmacogenetics of the response to lithium is concerned. Clearly, the ConLiGen project is a highly significant step in this research. Although the results of pharmacogenetic studies are of significant scientific value, their possible practical implications are yet to be seen.

Pharmacogenetics of lithium response in bipolar disorder

Bipolar disorder (BD) is a serious mental illness with well-established, but poorly characterized genetic risk. Lithium is among the best proven mood stabilizer therapies for BD, but treatment responses vary considerably. Based upon these and other findings, it has been suggested that lithium-responsive BD may be a genetically distinct phenotype within the mood disorder spectrum. This assertion has practical implications both for the treatment of BD and for understanding the neurobiological basis of the illness: genetic variation within lithium-sensitive signaling pathways may confer preferential treatment response, and the involved genes may underlie BD in some individuals. Presently, the mechanism of lithium is reviewed with an emphasis on gene-expression changes in response to lithium. Within this context, findings from genetic-association studies designed to identify lithium response genes in BD patients are evaluated. Finally, a framework is proposed by which future pharmacogenetic studies can incorporate advances in genetics, molecular biology and bioinformatics in a pathway-based approach to predicting lithium treatment response.

The promise and reality of pharmacogenetics in psychiatry

Existing psychotropic medications for the treatment of mental illnesses, including antidepressants, mood stabilizers, and antipsychotics, are clinically suboptimal. They are effective in only a subset of patients or produce partial responses, and they are often associated with debilitating side effects that discourage adherence. There is growing enthusiasm in the promise of pharmacogenetics to personalize the use of these treatments to maximize their efficacy and tolerability; however, there is still a long way to go before this promise becomes a reality. This article reviews the progress that has been made in research toward understanding how genetic factors influence psychotropic drug responses and the challenges that lie ahead in translating the research findings into clinical practices that yield tangible benefits for patients with mental illnesses.

Predicting response to lithium in bipolar disorder: a critical review of pharmacogenetic studies

BACKGROUND

It is difficult to reliably identify clinical predictors of lithium response. In recent years a number of pharmacogenetic studies have attempted to identify genetic variants which might be associated with response to lithium in bipolar patients.

AIMS

To critically review pharmacogenetic studies of lithium response in bipolar disorder and suggest strategies for future work in this field.

METHOD

Computerized searches of electronic databases for studies published between 1966 and October 2007. Studies were selected for detailed review according to the following criteria: (i) contained original data; (ii) included bipolar patients (including DSM-IV BP-I and BP-II); and (iii) lithium was the prophylactic agent under study.

RESULTS

One hundred and fifty studies of interest were identified but only 15 relevant papers were selected for detailed review based on the selection criteria. Despite some interesting preliminary findings, there are substantial methodological limitations with almost all of the studies published to date. These issues are critically reviewed.

CONCLUSIONS

The pharmacogenetics of lithium response in bipolar disorder remains a field in its infancy. There is a need for large-scale, prospective studies of biologically plausible candidate gene genes. The advent of genome-wide association studies holds particular promise for future studies.

Pharmacogenomics of mood stabilizers in the treatment of bipolar disorder

Bipolar disorder (BD) is a chronic and often severe psychiatric illness characterized by manic and depressive episodes. Among the most effective treatments, mood stabilizers represent the keystone in acute mania, depression, and maintenance treatment of BD. However, treatment response is a highly heterogeneous trait, thus emphasizing the need for a structured informational framework of phenotypic and genetic predictors. In this paper, we present the current state of pharmacogenomic research on long-term treatment in BD, specifically focusing on mood stabilizers. While the results provided so far support the key role of genetic factors in modulating the response phenotype, strong evidence for genetic predictors is still lacking. In order to facilitate implementation of pharmacogenomics into clinical settings (i.e., the creation of personalized therapy), further research efforts are needed.

The promise and reality of pharmacogenetics in psychiatry

Existing psychotropic medications for the treatment of mental illnesses, including antidepressants, mood stabilizers, and antipsychotics, are clinically suboptimal. They are effective in only a subset of patients or produce partial responses, and they are often associated with debilitating side effects that discourage adherence. There is growing enthusiasm in the promise of pharmacogenetics to personalize the use of these treatments to maximize their efficacy and tolerability; however, there is still a long way to go before this promise becomes a reality. This article reviews the progress that has been made in research toward understanding how genetic factors influence psychotropic drug responses and the challenges that lie ahead in translating the research findings into clinical practices that yield tangible benefits for patients with mental illnesses.

Common genetic, clinical, demographic and psychosocial predictors of response to pharmacotherapy in mood and anxiety disorders

The aim of this study is to summarize available knowledge about common genetic, clinical, demographic and psychosocial predictors of response to pharmacotherapy in mood and anxiety disorders. A literature search was carried out by using MEDLINE and references of selected articles. The search included articles published up to March 2008. The main genetic finding concerns the serotonin transporter gene promoter polymorphisms, the long variant of which seems to be related to a positive response to therapy in mood disorders and could also have a role in the treatment of anxiety disorders. Among other predictors, the main factors common to both classes of disorder are comorbid axis II disorders and early onset of illness, which are related to a worse response to therapy and concomitant good physical conditions, absence of earlier treatments, early administration and response to therapies, and higher self- directedness, which is related to a better outcome. Many common predictors have been identified and these seem to be related to features covering the totality of patients that go beyond specific characteristics of single disorders. Possible limitations and suggestions for future research based on a more integrated vision of human complexity are discussed.

A possible association between missense polymorphism of the breakpoint cluster region gene and lithium prophylaxis in bipolar disorder

Lithium is one of the most commonly used drugs for the treatment of bipolar disorder. To prescribe lithium appropriately to patients, predictors of response to this drug were explored, and several genetic markers are considered to be good candidates. We previously reported a significant association between genetic variations in the breakpoint cluster region (BCR) gene and bipolar disorder. In this study, we examined a possible relationship between response to maintenance treatment of lithium and Asn796Ser single-nucleotide polymorphism in the BCR gene. Genotyping was performed in 161 bipolar patients who had been taking lithium for at least 1 year, and they were classified into responders for lithium mono-therapy and non-responders. We found that the allele frequency of Ser796 was significantly higher in non-responders than in responders. Further investigation is warranted to confirm our findings.

Pharmacogenomics in Psychiatry

Pharmacogenomics may provide us with the means to expedite treatment for patients with various psychiatric disorders. Treatment is presently hampered by individual variation in medication response that often results in an extended trial-and-error process of treatment until the optimal medication is found. This can extend the time until treatment optimization to months or years. Much of this variation may be genetically based. This review discusses current pharmacogenomics research in mood disorders and in schizophrenia. Although the field is in an early stage, results already suggest that DNA tests will one day be of clinical value in the optimal selection of medications for mood and thought disorders.

Influence of the catechol-O-methyltransferase Val108/158Met polymorphism on the plasma concentration of catecholamine metabolites and on clinical features in type I bipolar disorder--a preliminary report

BACKGROUND

The activity of catechol-O-methyltransferase (COMT) may be related to psychosis susceptibility. The Val108/158Met polymorphism of the COMT gene influences its enzymatic activity and may result in altered concentrations of monoamine metabolites and different clinical responses of patients to pharmacological treatments.

METHODS

We examined in a sample of 42 bipolar patients if the Val108/158Met polymorphism influences: (a) the presence of psychosis in type I bipolar patients; (b) the blood plasma concentration of homovanillic acid (HVA) and 3-methoxy-4-hydroxyphenylglycol (MHPG), which are metabolites of dopamine and noradrenaline respectively and (c) the severity of the clinical characteristics of these patients and their response to pharmacological treatment.

RESULTS

No significant associations were found between the studied COMT genotypes and the studied parameters. However, a non-significant aggregation of bipolar patients presenting with psychosis was found in the homozygous Val-Val group. Clinical improvement was found to significantly correlate with the levels of plasma MHPG prior to treatment. Moreover, a significant difference was found between the standard deviations of the concentrations of HVA in the three genotypes, but not in their mean values. Significant associations were not detected between COMT polymorphisms and the initial severity of the disorder, or the clinical response to pharmacological treatment.

LIMITATIONS

The size of the studied sample is somewhat small and comparisons have been made with a previously studied control group.

CONCLUSIONS

The Val108/158Met polymorphism does not appear to be a crucial determinant in type I bipolar disorder.

Investigating responders to lithium prophylaxis as a strategy for mapping susceptibility genes for bipolar disorder

Attempts to map susceptibility genes for bipolar disorder have been complicated by genetic complexity of the illness and, above all by heterogeneity. This paper reviews the genetic research of bipolar disorder aiming to reduce the heterogeneity by focusing on definite responders to long-term lithium treatment. The available evidence strongly suggests that lithium-responsive bipolar disorder is the core bipolar phenotype, characterized by a more prominent role of genetic factors. Responders to lithium have typically a family history of bipolar disorder (often responsive to lithium). They differ from responders to other mood stabilizing drugs in their family histories as well as in other clinical characteristics. The molecular genetic investigations of bipolar disorder responsive to lithium indicate possibly several loci linked to and/or associated with the illness. A combination of research strategies employing multiple methods such as linkage, association, and gene-expression studies will be needed to clarify which of these represent true susceptibility loci.

Pharmacogenetics of selective serotonin reuptake inhibitor response: a 6-month follow-up

BACKGROUND

We previously reported the association between some genetic factors and short-term antidepressant outcome. In the present paper we investigated the same gene variants in a prospective 6-months naturalistic follow-up.

METHODS

The sample included 185 inpatients affected by recurrent major depression consecutively admitted to the Psychiatric Inpatient Unit of San Raffaele Hospital from 1998 to 2003 and prospectively followed for 6 months after their recovery. All the patients were undertaking continuation therapy. The functional polymorphism in the upstream regulatory region of the serotonin transporter gene (SERTPR), the tryptophan hydroxylase A218C substitution, a VNTR polymorphism located 1.2 kb upstream of the monoamine oxidase-A coding sequences, the CLOCK gene T3111C and the PER3exon15 gene T1940G substitutions were analysed, using PCR-based techniques.

RESULTS

No association was found between clinical variables and relapses; subjects showing TT genotype at CLOCK gene tended to relapse within 6 months after recovery more than TC and CC subjects taken together. A non-significant tendency of SERTPR*s/s subjects to a minor frequency of relapse was also observed.

CONCLUSION

Some subjects showing remission after acute treatment relapsed within 6 months, despite undertaking a maintenance treatment; the causes could be heterogeneous, but CLOCK gene variants may influence the outcome.

Pharmacogenetics in the treatment of depression: pharmacodynamic studies

The pharmacological treatment of mood disorders has reduced their morbidity and improved mental health for millions of individuals worldwide, favouring a considerable reduction of the direct and indirect costs caused by these common pathologies. Unfortunately, not all individuals benefit, and 30-40% of patients do not show a complete response to treatment. Efficient clinical predictors are not available, although genetic factors are thought to play a substantial (but complex) role in the antidepressant response. Pharmacogenetics, which investigates the influence of genetic features on the pharmacological response, has gained increasing attention and holds great promise for clinical psychiatry. Here, a brief overview is provided on the various pharmacogenetic studies published to date that analyse the commonest treatments for depression: antidepressants, sleep deprivation and lithium salts.

Pharmacogenetics and mood stabilization in bipolar disorder

Bipolar disorder is a severe psychiatric disease characterized by varying treatment response among individual patients. Effects of certain treatments, for instance, lithium, can be predicted from clinical characteristics of patients and their family histories. This led to a suggestion that a treatment response could identify subtypes of bipolar disorder particularly suited for gene-mapping studies. In this paper we review family and molecular studies of bipolar disorder responsive to lithium, as well as studies aiming to identify polymorphisms associated with the treatment response itself. While molecular genetic research and gene expression studies promise to bring new insights into the pathophysiology of the illness and the nature of treatment response, and thus provide new information for better treatment of bipolar disorder in the future, results from family studies and studies of clinical correlates of treatment response may already be utilized in the management of bipolar disorder.

Pharmacogenetics and bipolar disorder

Bipolar disorder (BD) is a major psychiatric condition that commonly requires prophylactic and episodic treatment. There is important variability in the therapeutic response and side-effect profiles to currently available pharmacological agents. Pharmacogenetics have provided new hopes to develop more efficient treatment strategies tailored to the individual patient's needs. This review assesses nonsystematically studies using pharmacogenetic strategies in BD. Most of these studies have focused on patients selected according to lithium response, and more recently, a growing number of studies have been investigating genetic factors in mixed samples of patients classified according to response to antidepressant treatment. Although previous clinical and family studies support the use of pharmacogenetic strategies both to increase phenotype homogeneity as well as to identify genetic factors that may mediate response to treatment, most molecular studies carried out to date are still preliminary and in need of external validation. A major problem has been comparability between studies, in part, because of differences in the criteria used to define response. More attention should be paid to standardize the criteria for drug response definition.

Long-term responsiveness to lithium as a pharmacogenetic outcome variable: treatment and etiologic implications

The importance of genes in the etiology of bipolar disorder has been substantiated through family, twin, and adoption studies. Bipolar disorder is treated at the prophylactic and episodic levels; lithium is one of the most common forms of prophylactic treatment. Recently, pharmacogenetics has come to play an active role in the elucidation of genetic factors that may play a role in modulating lithium response. This strategy has provided hope for advancements in understanding the genetics of lithium-responsive bipolar disorder. This review encompasses studies that have used populations of lithium responders and non-responders to carry out family, linkage, or association studies, as well as some insight into possible mechanisms by which lithium produces its prophylactic effect. Although data examining the pharmacogenetics of bipolar disorder remain scarce, this is a promising avenue of investigation to help genetically define more homogeneous populations or to search for genetic predictors of drug response.

Predicting response to lithium in mood disorders: role of genetic polymorphisms

Lithium is considered to be the first choice mood stabilizer in recurrent mood disorders. Its widespread and large-scale use is the result of its proven efficacy. In spite of this fact, patients have been observed to show a variable response to lithium treatment: in some cases it is completely effective in preventing manic or depressive relapses, while in other cases it appears to show no influence on the disease course. The possible definition of a genetic liability profile for adverse effects and efficacy will be of great help, as lithium therapy needs at least 6 months to be effective in stabilizing mood disorders. During the last few years, a number of groups have reported possible liability genes. Lithium long-term prophylactic efficacy has been associated with serotonin transporter protein, tryptophan hydroxylase and inositol polyphosphate 1-phosphatase variants. A number of other candidate genes and anonymous markers did not yield positive associations. Therefore, even if some positive results have been reported, no unequivocal susceptibility gene for lithium efficacy has been identified. Although the available data may not currently allow a meaningful prediction of lithium response, future research is aimed at the development of individualized treament of mood disorders, including the possibility of 'pharmacological genetic counseling'.

Biological predictors of lithium response in bipolar disorder

In order to prescribe lithium appropriately to patients with bipolar disorder, predictors of lithium response are helpful. The present paper reviews the biological predictors of lithium response. As a positive predictor of lithium response, the following have been reported: strong loudness dependence of the auditory-evoked N1/P2-response; higher brain lithium concentration; lower inositol monophosphatase (IMPase) mRNA expression; higher serotonin-induced calcium mobilization; increased N-acetyl-aspartate peak and decreased myo-inositol peak; white matter hyperintensity; decreased intracellular pH; higher frequency of phospholipase C gamma-1 (PLCG1)-5 repeat and PLCG1-8 repeat; and C973A polymorphism in the inositol polyphosphate 1-phosphatase gene. In contrast the following have been reported as a predictor of negative lithium response: epileptiform abnormality of electroencephalography; human leukocyte antigen type A3; decreased phosphocreatine peak area after photic stimulation; and homozygotes for the short variant of the serotonin transporter gene. Most of the possible biological predictors of better lithium response, such as lower IMPase mRNA levels, white matter hyperintensity, lower brain intracellular pH, enhanced calcium response, and PLCG1-5 repeat had been detected as risk factors for bipolar disorder, suggesting that bipolar disorder responding well to maintenance lithium treatment is a distinct category having a certain neurobiological basis, although these findings need further replication. The search for biological predictors of lithium response is still in its infancy. Most of the laboratory or neuroimaging techniques used in these studies are not easily performed in clinical settings, so the development of an easy and useful laboratory test is needed.

Pharmacogenetic aspects of bipolar disorder

This paper reviews current knowledge of genetic factors in the treatment of bipolar disorder. Most studies to date have investigated genetic differences between responders and non-responders to lithium. The most provocative findings have been obtained in studies of serotonin transporter gene. Another promising application of pharmacogenetic research is the identification of subgroups of bipolar disorder defined by response (or non-response) to pharmacological treatments. Such subgroups could be used to define more homogeneous patient populations for gene-mapping studies.