Lithium-responsive affective disorders: no association with the tyrosine hydroxylase gene

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.

Sex-specific effects of LiCl treatment on preservation of renal function and extended life-span in murine models of SLE: perspective on insights into the potential basis for survivorship in NZB/W female mice

Considerable research effort has been invested in attempting to understand immune dysregulation leading to autoimmunity and target organ damage. In systemic lupus erythematosus (SLE), patients can develop a systemic disease with a number of organs involved. One of the major target organs is the kidney, but patients vary in the progression of the end-organ targeting of this organ. Some patients develop glomerulonephritis only, while others develop rapidly progressive end organ failure. In murine models of SLE, renal involvement can also occur. Studies performed over the past several years have indicated that treatment with LiCl of females, but not males of the NZB/W model, at an early age during the onset of disease, can prevent development of end-stage renal disease in a significant percentage of the animals. While on Li treatment, up to 80 % of the females can exhibit long-term survival with evidence of mild glomerulonephritis which does not progress to renal failure in spite of on-going autoimmunity. Stopping the treatment led to a reactivation of the disease and renal failure. Li treatment of other murine models of SLE was less effective and decreased survivorship in male BxSB mice, exhibited little effect on male MRL-lpr mice, and only modestly improved survivorship in female MRL-lpr mice. This perspective piece discusses the findings of several related studies which support the concept that protecting target organs such as the kidney, even in the face of continued immune insults and some inflammation, can lead to prolonged survival with retention of organ function. Some possible mechanisms for the effectiveness of Li treatment in this context are also discussed. However, the detailed mechanistic basis for the sex-specific effects of LiCl treatment particularly in the NZB/W model remains to be elucidated. Elucidating such details may provide important clues for development of effective treatment for patients with SLE, ~90 % of which are females.

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.

Gene-expression differences in peripheral blood between lithium responders and non-responders in the Lithium Treatment-Moderate dose Use Study (LiTMUS)

This study was designed to identify genes whose expression in peripheral blood may serve as early markers for treatment response to lithium (Li) in patients with bipolar disorder. Although changes in peripheral blood gene-expression may not relate directly to mood symptoms, differences in treatment response at the biochemical level may underlie some of the heterogeneity in clinical response to Li. Subjects were randomized to treatment with (n=28) or without (n=32) Li. Peripheral blood gene-expression was measured before and 1 month after treatment initiation, and treatment response was assessed after 6 months. In subjects treated with Li, 62 genes were differentially regulated in treatment responders and non-responders. Of these, BCL2L1 showed the greatest difference between Li responders and non-responders. These changes were specific to Li responders (n=9), and were not seen in Li non-responders or patients treated without Li, suggesting that they may have specific roles in treatment response to Li.

Molecular linkage studies of bipolar disorder

Linkage studies have defined at least five bipolar (BP) disorder susceptibility loci that meet suggested guidelines for initial identification and subsequent confirmation. These loci, found on 18p11, 18q22, 21q21, 4p16, and Xq26, are targets for BP candidate gene investigations. Molecular dissection of expressed sequences for these regions is likely to yield specific BP susceptibility alleles in most cases, in all probability, these BP susceptibility alleles will be common in the general population, and, individually, will be neither necessary nor sufficient for manifestation syndrome. Additive or multiplicative oligogenic models involving several susceptibility loci appear most reasonable at present, it is hoped thai these BP susceptibility genes will increase understanding of many mysteries surrounding these disorders, including drug response, cycling patterns, age-of-onset, and modes of transmission.

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.

Response to treatment in bipolar disorder

PURPOSE OF REVIEW

Bipolar disorder is a complex psychiatric condition that has been shown to carry a great degree of genetic loading. This review addresses current research in the genetics of treatment response in bipolar disorder, with a focus on findings that have shaped our understanding of the changing direction of this field in light of recent technological advancements.

RECENT FINDINGS

The recent publications in bipolar disorder treatment response have helped consolidate or improve upon knowledge of susceptibility loci and genes in the field. There seems to be an increasing trend toward functionally assessing the role played by putative candidate genes and molecular factors modulating expression in bipolar disorder, as well as a movement toward more global, pathway and genome-wide-oriented research.

SUMMARY

Genetic and molecular research to date in bipolar disorder treatment response has not completely answered all the lingering questions in the field, but has contributed to the development of a more patient-based understanding of treatment. In order to apply these findings at a clinical level, more comprehensive treatment response studies are imperative, combining recent advances in high-throughput genomics with functional molecular research.

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.

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.

Further evidence for a possible association between serotonin transporter gene and lithium prophylaxis in mood disorders

We previously reported an association between the functional polymorphism in the upstream regulatory region of the serotonin transporter gene (SERTPR) and the prophylactic efficacy of lithium in a sample of 201 Italian subjects affected by Mood disorders. The aim of the present study was to replicate analyses on an independent sample. In total, 83 subjects affected by Bipolar disorder were recruited in the Mood Disorders Clinic of the Eginition Hospital of the Athens University, Medical School Department of Psychiatry. All patients were administered with lithium as prophylactic therapy and they were prospectively observed for at least 3 years. Subjects were typed for their SERTPR variant using polymerase chain reaction techniques. SERTPR variants were associated with lithium outcome among those subjects who had few manic episodes before lithium treatment and, as a trend, among subjects who received a high daily dose of lithium (> or =1200 mg/die). In both cases, subjects with the l/l variant showed a higher probability to develop an illness episode within 3 years of prophylactic treatment with lithium. The present study confirmed our previous observation of a better response of SERTPR*l/s carriers, but could not confirm a poor efficacy in subjects with the SERTPR*s/s genotype. Notwithstanding the conflicting results, SERTPR variants are a possible liability factor for lithium long-term efficacy in mood disorders. Further studies on independent and large samples are required to determine the reliability and direction of the possible association between SERTPR variants and lithium 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'.

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.

Post-genomic era and gene discovery for psychiatric diseases: there is a new art of the trade? The example of the HUMTH01 microsatellite in the Tyrosine Hydroxylase gene

The microsatellite HUMTH01, located in the first intron of the Tyrosine Hydroxylase (TH) gene (encoding the rate-limiting enzyme in the synthesis of catecholamines), is characterized by a TCAT repeated motif and has been used in genetic studies of neuropsychiatric and other complex diseases, in which catecholaminergic neurotransmission is implicated. After reporting a positive association between HUMTH01 and bipolar disorder as well as schizophrenia, the authors established that HUMTH01 alleles display the features of regulatory elements. Thereafter, they cloned two proteins (ZNF191 and HBP1), specifically binding to HUMTH01, and demonstrated that allelic variations of HUMTH01 have a quantitative silencing effect on TH gene expression in vitro, and correlate with quantitative and qualitative changes in the binding by ZNF191. The authors aim to characterize the transduction pathway impinging on the HUMTH01 microsatellite and establish its relevance for TH gene regulation in vivo. Since the TCAT repeated sequence is widespread throughout the genome, their approach may lead to the dissection of the mechanisms underlying the quantitative expression of several genes implicated in complex genetic traits, both normal and pathological. Thus, these investigations on the possible contribution and potential role of the HUMTH01 microsatellite in neuro-pathological conditions may represent an example of the different approaches needed to validate genetic targets in the "post-genomic era."

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

We studied the possible association between the prophylactic efficacy of lithium in mood disorders and the following gene variants: catechol-O-methyltransferase (COMT) G158A, monoamine oxydase A (MAO-A) 30-bp repeat, G-protein beta 3-subunit (Gbeta3) C825T. A total of 201 subjects affected by bipolar (n = 160) and major depressive (n = 41) disorder were followed prospectively for an average of 59.8 months and were typed for their gene variants using PCR techniques. COMT, MAO-A, and Gbeta3 variants were not associated with lithium outcome, even when possible stratification effects such as sex, polarity, age at onset, duration of lithium treatment, and previous episodes were included in the model. The pathways influenced by those variants are not therefore involved with long-term lithium outcome in our sample.

Serotonin transporter gene associated with lithium prophylaxis in mood disorders

The aim of this study was to investigate the possible association between the functional polymorphism in the upstream regulatory region of the serotonin transporter gene (5-HTTLPR) and the prophylactic efficacy of lithium in mood disorders. Two hundred and one subjects affected by bipolar (n = 167) and major depressive (n = 34) disorder were followed prospectively for an average of 58.2 months and were typed for their 5-HTTLPR variant using polymerase chain reaction techniques. 5-HTTLPR variants were associated with lithium outcome (F = 5.35; df = 2,198; P = 0.005). Subjects with the s/s variant showed a worse response compared to both l/s and l/l variants. Consideration of possible stratification effects such as sex, polarity, age at onset, duration of lithium treatment and previous episodes did not influence the observed association. 5-HTTLPR variants may be a possible influencing factor for the prophylactic efficacy of lithium in mood disorders.

Pharmacogenetics of bipolar disorder

To review the pharmacogenetics of bipolar disorders, the authors searched databases for genetic association and linkage studies involving response to long-term prophylactic lithium treatment, as well as treatment with antidepressants or clozapine. Significant ethnic variations in the metabolism and efficacy of antidepressants, as well as clozapine, have been reported by several groups. Systematic studies suggest that that genetic factors affect the response to prophylactic lithium treatment. Numerous associations between the three traits of interest and candidate gene polymorphisms have been proposed. Among these, an association between the serotonin transporter gene and response to serotonin reuptake inhibitors appears robust. Considerable interest has also focused on serotonergic gene polymorphisms and response to clozapine. Response to pharmacotherapy in bipolar disorders may be mediated by genetic factors, but the role played by heritability is unknown.

Pharmacogenetics in affective disorders

Pharmacogenetics will be of substantial help in the field of affective disorders pharmacotherapy. The possible definition of a genetic liability profile for drug side-effects and efficacy will be of great help in treatments that need weeks to months to be effective. During the last few years, a number of groups have reported possible liability genes. The efficacy and time of onset of selective serotonin reuptake inhibitors have been associated with a polymorphism in the promoter region of the transporter (SERTPR) in many independent studies, while variants at the tryptophan hydroxylase gene, 5-HT2a receptor and G-protein beta3 have been associated with them in pilot studies. Lithium long-term prophylactic efficacy has been associated with SERTPR, TPH and inositol polyphosphate 1-phosphatase variants, though in unreplicated samples. A number of further candidate genes were not associated with these treatments. In conclusion, both acute and long-term treatments appear to be, at least to some extent, under genetic influence and preliminary data have identified possible liability genes.

Lithium long-term treatment in mood disorders: clinical and genetic predictors

Lithium is the most widely used long-term treatment for recurrent mood disorders. Despite its proven efficacy, patients show a variable response, ranging from complete efficacy to no influence at all. This paper reviews possible predictors of response focusing on molecular genetic studies. The functional polymorphism in the upstream regulatory region of the serotonin transporter gene (5-HTTLPR) has been associated with lithium long-term efficacy in two independent studies, marginal associations have been reported for tryptophan hydroxylase and inositol polyphosphate 1-phosphatase (INPP1). A number of other candidate genes and anonymous markers did not yield positive associations. Therefore, even though some positive results have been reported, no unequivocal susceptibility gene for lithium efficacy has been identified.

Genetic factors and treatment of mood disorders

OBJECTIVES

This paper reviews the pharmacogenetics of mood disorders.

METHODS

We have searched the literature for published studies and abstracts relevant for genetic effects in acute antidepressant treatment and in long-term prophylactic treatment.

RESULTS

The most promising findings to date show an association of the serotonin transporter (5-HTT) gene and the response to serotonin reuptake inhibitors. Genetic factors also appear to play a significant role in the outcome of long-term lithium treatment. The phenotype of lithium-responsive bipolar disorder is associated with stronger genetic effects as well as with an increased phenotypic homogeneity.

CONCLUSIONS

Genetic factors likely influence treatment response in mood disorders. Clarifying their precise role will have implications for treatment as well as for understanding the pathophysiological mechanisms of these disorders.

Tryptophan hydroxylase gene associated with paroxetine antidepressant activity

The possible association of the A218C tryptophan hydroxylase (TPH) gene variant with the antidepressant activity of paroxetine was investigated in a sample of 121 inpatients affected by a major depressive episode and treated with paroxetine 20-40 mg with either placebo or pindolol in a double blind design for 4 weeks. The severity of depressive symptoms was weekly assessed with the Hamilton Rating Scale for Depression. TPH allelic variants were determined in each subject using a PCR-based technique. TPH*A/A and TPH*A/C variants were associated with a poorer response to paroxetine treatment when compared to TPH*C/C (P=0.005); this difference was not present in the pindolol augmented group. Other variables, such as sex, diagnosis, presence of psychotic features, severity of depressive symptomatology at baseline and paroxetine plasma level, were not associated with the outcome. TPH gene variants are therefore a possible modulator of paroxetine antidepressant activity.

Factors affecting fluvoxamine antidepressant activity: influence of pindolol and 5-HTTLPR in delusional and nondelusional depression

BACKGROUND

It has been recently reported that the short variant of the serotonin transporter (5-HTT) gene-linked functional polymorphic region (5-HTTLPR) influences the antidepressant response to certain selective serotonin reuptake inhibitors. The aim of the present study was to test this finding in a sample of major and bipolar depressives, with or without psychotic features.

METHODS

One hundred fifty-five inpatients were treated with fluvoxamine 300 mg and either placebo or pindolol in a double-blind design for 6 weeks. The severity of depressive symptoms was weekly assessed with the Hamilton Rating Scale for Depression. Allelic variation of 5-HTTLPR in each subject was determined using a polymerase chain reaction-based technique.

RESULTS

5-HTTLPR short variant was associated with a poor response to fluvoxamine treatment, independently from the recorded clinical variables. More specifically, the diagnosis, the presence of psychotic features, and the severity of depressive symptomatology did not influence this association. Conversely, pindolol augmentation may ameliorate the rate of response in 5-HTTLPR short variant subjects, thus reducing the difference in the response rate among the genotype variants.

CONCLUSIONS

If confirmed, these results may improve patient care by helping the clinician to individualize treatment according to the patient's genetic 5-HTTLPR pattern.

Lithium-related genetics of bipolar disorder

Lithium is a potent prophylactic medication and mood stabilizer in bipolar disorder. However, clinical outcome is variable, and its therapeutic effect manifests after a period of chronic treatment, implying a progressive and complex biological response process. Signal transduction systems known to be perturbed by lithium involve phosphoinositide (PI) turnover, activation of the Wnt pathway via inhibition of glycogen synthase kinase-3beta (GSK-3beta), and a growth factor-induced, Akt-mediated signalling that promotes cell survival. These pathways, acting in synergy, probably prompt the amplification of lithium signal causing such immense impact on the neuronal network. The sequencing of the human genome presents an unparallelled opportunity to uncover the full molecular repertoire involved in lithium action. Interrogation of high-resolution expression microarrays and protein profiles represents a strategy that should help accomplish this goal. A recent microarray analysis on lithium-treated versus untreated PC12 cells identified multiple differentially altered transcripts. Lithium-perturbed genes, particularly those that map to susceptibility regions, could be candidate risk-conferring factors for mood disorders. Transcript and protein profiling in patients could reveal a lithium fingerprint for responsiveness or nonresponsiveness, and a signature motif that may be diagnostic of a specific phenotype. Similarly, lithium-sensitive gene products could provide a new generation of pharmacological targets.

Serotonin receptor 2A, 2C, 1A genes and response to lithium prophylaxis in mood disorders

The aim of this study was to investigate the influence of serotonin receptors 2A, 2C and 1A gene variants on lithium prophylactic efficacy in mood disorders. One hundred and twenty-four subjects affected by bipolar (n=102) and major depressive (n=22) disorder were followed prospectively for an average of 52 months and were typed for 5-HT2A (T102C: n=111, HTP: n=104), 5-HT2C (n=110) and 5-HT1A (n=61) variants. Both 5-HT2A and 5-HT2C variants were not associated with lithium outcome. Consideration of possible stratification effects like gender, polarity, family history, age at onset and duration of lithium treatment did not influence results. No 5-HT1A gene variant was identified. 5-HT2A and 2C variants are not, therefore, associated with lithium prophylactic efficacy in mood disorders.

Searching high and low: a review of the genetics of bipolar disorder

OBJECTIVES

To review the methodologies and findings in the genetics of bipolar disorder (BPD), and to suggest future directions for research.

METHODS

Reports of family, twin, adoption, linkage, association, cytogenetic, and animal model studies, and segregation analyses in English, were identified from multiple MEDLINE searches. Hand searches were carried out in bibliographies from review articles.

RESULTS

Family, twin, and adoption studies have provided strong evidence for a genetic etiology in BPD. Early reports of linkage of BPD to DNA markers at several chromosomal sites have not proven robust, perhaps because of the complex nature of BPD inheritance. However, linkage findings in the 1990s, on chromosomes 18, 21q, 12q, and 4p, have provided leads that are being pursued through both genetic and physical mapping. No gene has yet been definitively implicated in BPD.

CONCLUSIONS

Strategies for increasing the power to detect BPD genes include: (1) dividing the phenotype into genetically meaningful subtypes to decrease heterogeneity: and (2) ascertaining a very large family sample--a multicenter study now in progress will collect 700 bipolar I sibling pairs. BPD may result from several genes acting in concert so that new multilocus statistical methods could enhance the capacity to detect loci involved. Family-based association studies using a very large number of newly identified single nucleotide polymorphisms (SNPs) may allow for more efficient screening of the genome. As the Human Genome Project approaches its goal of isolating all genes by 2003, the data generated is likely to speed identification of candidate BPD genes.

Tryptophan hydroxylase gene and response to lithium prophylaxis in mood disorders

Lithium is an effective prophylactic agent in mood disorders but not all patients with mood disorders respond to lithium therapy; it is therefore necessary to identify responders prior to treatment. Clinical predictors account for about half of the variance and it is probable that genetic factors play a substantial role. The aim of this study was to investigate the possible association between the tryptophan hydroxylase (TPH) gene and prophylactic efficacy of lithium in mood disorders. One hundred and eight subjects affected by bipolar (n = 90) and major depressive (n = 18) disorder were followed prospectively for an average of 50.4 months and were typed for their TPH variant using polymerase chain reaction techniques. TPH variants were marginally associated with lithium outcome (F = 3.16; d.f.=2,105; P = 0.046). Subjects with the TPH*A/A variant showed a trend toward a worse response compared to both TPH*A/C and TPH*C/C variants. Consideration of possible stratification effects such as gender, polarity or age at onset did not influence the observed association. TPH variants may be a possible factor influencing the prophylactic efficacy of lithium in mood disorders.

Dopamine receptor D2 and D4 genes, GABA(A) alpha-1 subunit genes and response to lithium prophylaxis in mood disorders

Lithium is an effective prophylactic agent in mood disorders, and genetic factors are likely to modulate individual susceptibility to lithium treatment. The aim of this study is to investigate the influence of dopamine receptor D2 (DRD2), D4 exon 3 (DRD4), and gamma-aminobutyric acid type A (GABA(A)) receptor alpha-1 subunit (GABRA1) gene variants on the efficacy of lithium prophylaxis in mood disorders. Patients with mood disorders (N = 125: bipolar subtype, n = 100; major depressive disorder subtype, n = 25) were followed prospectively for an average of 53 months and were typed for DRD2 (Ser311/Cys311: n = 121, VNTR: n = 63), DRD4 (n = 125) and GABRA1 (n = 61) variants using polymerase chain reaction (PCR) techniques. DRD2, DRD4 and GABRA1 variants were not associated with response to lithium. A trend was observed toward a better outcome of DRD4* 2/4 subjects, but it was due to only two subjects. Consideration of possible stratification effects like gender, polarity, family history, age at onset and duration of lithium treatment did not reveal any association either. DRD2, DRD4 and GABRA1 variants therefore do not appear to be associated with the outcome of lithium prophylaxis in mood disorders.

Analysis and metaanalysis of two polymorphisms within the tyrosine hydroxylase gene in bipolar and unipolar affective disorders

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the synthesis of dopamine and noradrenaline. While positive associations between TH and bipolar affective disorder have been found in several studies, many studies have failed to reproduce these results. In order to clarify this situation, association studies of bipolar and unipolar affective disorder groups and metaanalyses of published data on the TH tetranucleotide repeat polymorphism were done. The association studies used the TH tetranucleotide repeat polymorphism in intron 1 and a PstI polymorphism at the 3' end of the gene. The study comprised 124 unrelated bipolar patients, 126 unipolar patients, and 242 controls. There was no significant association of either bipolar or unipolar affective disorder with the TH tetranucleotide repeat polymorphism. However, a weak association (chi2 = 3.946, 1 df, P = 0.047; odds ratio, allele 2 vs. allele 1 = 0.71 (95% CI, 0.51-0.996)) was observed in the unipolar sample with the TH-PstI polymorphism. Three metaanalyses of published data on the TH tetranucleotide repeat polymorphism in major affective disorder were performed: bipolar I + II vs. control using 583 cases and 745 controls; unipolar vs. control using 204 cases and 359 controls; and bipolar + unipolar vs. control using 846 cases and 823 controls. In each analysis there was no association of the TH tetranucleotide repeat polymorphism and affective disorder. These results do not support the tyrosine hydroxylase gene having a major role in the etiology of bipolar affective disorder. However, our data suggest that this locus should be examined in larger samples of unipolar affective disorder.

Bipolar disorder: from families to genes

BACKGROUND

Genetic factors are known to contribute to the etiology of bipolar illness, but the actual genetic mechanisms remain to be clarified.

METHODS

This paper reviews the research undertaken to establish the genetic basis of bipolar illness and to elucidate the nature of its genetic predisposition.

RESULTS

The presented findings suggest that bipolar affective disorder is a heterogeneous condition characterized by a complex relationship between the genetic susceptibility and the clinical presentation. Linkage studies have generated promising and replicated findings on chromosomes 18 and 21.

CONCLUSION

In spite of the methodological difficulties inherent in the genetic study of psychiatric disorders recent investigations have made important advances and promise to identify specific susceptibility genes.