Response to Zhang et al. (2005) Loss-of-Function Mutation in Tryptophan Hydroxylase-2 Identified in Unipolar Major Depression. Neuron 45, 11–16

Influence of TPH2 and HTR1A polymorphisms on lifelong premature ejaculation risk among the chinese Han population

BACKGROUND

Lifelong premature ejaculation (LPE) is one of the most common ejaculatory dysfunctions in men. The serotonin (5-HT) synthesis rate-limiting enzyme (TPH2) and receptor (HTR1A) in the 5-HT regulatory system may play a key role in the pathogenesis of LPE. However, there are few studies on the effects of TPH2 and HTR1A polymorphisms on LPE risk. We speculated that TPH2 and HTR1A polymorphisms may affect the occurrence and development of LPE in the Chinese Han population.

METHODS

In this study, 91 patients with LPE and 362 normal controls aged 18 to 64 years were enrolled in the male urology department of Hainan General Hospital in China from January 2016 to December 2018. The SNPs in HTR1A and TPH2, which are related to 5-HT regulation, were selected as indexes to genotype the collected blood samples of participants. Logistic regression was used to analyze the correlation between SNPs of HTR1A and TPH2 with LPE susceptibility, as well as the relationship with leptin, 5-HT and folic acid levels.

RESULTS

The results revealed that HTR1A-rs6295 increased LPE risk in recessive model. Rs11178996 in TPH2 significantly reduced susceptibility to LPE in allelic (odds ratio (OR) = 0.68, 95% confidence interval (95% CI) = 0.49-0.96, p = 0.027), codominant (OR = 0.58, 95% CI = 0.35-0.98, p = 0.040), dominant (OR = 0.58, 95% CI = 0.36-0.92, p = 0.020), and additive (OR = 0.71, 95% CI = 0.52-0.98, p = 0.039) models. G_rs11179041T_rs10879352 could reduce the risk of LPE (OR = 0.44, 95% CI = 0.22-0.90, p = 0.024) by haplotype analysis.

CONCLUSION

HTR1A-rs6295 and TPH2-rs11178996 are associated with LPE risk in the Chinese Han population based on the finding of this study.

Polymorphism of TPH2 Gene rs120074175 Is Not Associated with Risk Factors of Schizophrenia

CONTEXT

Polymorphism on tryptophan hydroxylase 2 (TPH2) gene rs120074175 can cause the synthesis of neurotransmitter serotonin in the brain to reduce up to 80%. Reduced serotonin in the brain can cause dopamine release to occur continuously. Excess dopamine in the brain may cause positive symptom of schizophrenia.

AIM

The aim of this study was to investigate the genotype distribution of TPH2 rs120074175 gene on patients with schizophrenia at Prof. Dr. Soerojo Magelang Psychiatric Hospital, Indonesia, and the relationship between the genetic polymorphism of the TPH2 rs120074175 gene against risk factors of schizophrenia.

SETTINGS AND DESIGN

This was a cross-sectional study.

MATERIALS AND METHODS

The method used was amplification refractory mutation system-polymerase chain reaction (ARMS-PCR). Whole blood from healthy subjects and patients with schizophrenia, Wizard genomic deoxyribonucleic acid (DNA) purification kit (Promega, Fitchburg, Wisconsin), PCR master mix (Promega), ARMS-PCR primers, ddH2O, agarose (Thermo Scientific, Seoul, South Korea), Tris, Acetic Acid, EDTA (TAE) 1X, ethidium bromide, loading dye 6×, and DNA ladder (Thermo Scientific) were the materials used.

STATISTICAL ANALYSIS

Hardy-Weinberg equilibrium and chi-square (χ2) tests were used.

RESULTS

The results showed that both groups (healthy subjects and patients with schizophrenia) at the Prof. Dr. Soerojo Magelang Psychiatric Hospital have a wild-type GG genotype (100%) without anyone having a mutant A allele.

CONCLUSION

TPH2 rs120074175 gene polymorphism was not associated with risk factors for schizophrenia.

Tryptophan hydroxylase(2) gene polymorphisms predict brain serotonin synthesis in the orbitofrontal cortex in humans

Brain regional serotonin synthesis can be estimated in vivo using positron emission tomography (PET) and α-[((11))C]methyl-L-tryptophan ((11)C-AMT) trapping (K*) as a proxy. Recently, we reported evidence of lower normalized (11)C-AMT trapping in the orbitofrontal cortex (OBFC) of subjects meeting the criteria for an impulsive and/or aggressive behavioral phenotype. In this study, we examined whether part of the variance in OBFC serotonin synthesis is related to polymorphisms of the gene that encodes for the indoleamine's rate-limiting enzyme in the brain, tryptophan hydroxylase-2 (TPH(2)). In all, 46 healthy controls had PET (11)C-AMT scans and were genotyped for 11 single-nucleotide polymorphisms (SNPs) distributed across the TPH(2) gene and its 5' upstream region. Several TPH(2) SNPs were associated with lower normalized blood-to-brain clearance of (11)C-AMT in the OBFC. Dose-effect relationships were found for two variants (rs6582071 and rs4641527, respectively, located in the 5' upstream region and intron 1) that have previously been associated with suicide. Associations in the OBFC remained statistically significant in a mixed larger sample of patients and controls. These results suggest that in humans, genetic factors might partly account for variations in serotonin synthesis in the OBFC.

TPH2 gene polymorphisms and major depression--a meta-analysis

BACKGROUND

Tryptophan hydroxylase-2 (TPH2) is the rate-limiting enzyme in the synthetic pathway for brain serotonin and is considered key factor for maintaining normal serotonin transmission in the central neuron system (CNS). Gene-disease association studies have reported a relationship between TPH2 and major depressive disorder (MDD) in different populations, however subsequent studies have produced contradictory results.

OBJECTIVES

We performed a systematic overview and a meta-analysis with all available data up-to-date.

METHODS

We scrutinized PubMed, Embase, HuGNet and China National Knowledge Infrastructure (CNKI ) and last update was held on October 2011. We also searched the manuscripts and the supplementary documents of the published genome-wide association studies in the field. Effect sizes of independent loci that have been studied in more than 3 articles were synthesized using fixed and random effects models.

RESULTS

We found 27 eligible articles that studied a total of 74 single nucleotide polymorphisms (SNPs). Finally, 12 independent loci were included in the meta-analysis. The synthesis of the data shown that two SNPs (rs4570625 and rs17110747) were associated with MDD using fixed effects models. SNP rs4570625 had low heterogeneity and remained significant using the more conservative random effects calculations with a summary OR = 0.83 (95% CI: 0.73-0.96).

CONCLUSION

The current study identified a SNP (rs4570625) with strong epidemiological credibility; however more studies are required to provide robust evidence for other weak associations.

The genetics of major depression: moving beyond the monoamine hypothesis

Efforts to unlock the biology of major depressive disorder (MDD) are proceeding on multiple fronts. In this article, the authors review the current understanding of epidemiological evidence for a heritable component to MDD risk, as well as recent advances in linkage, candidate gene, and genome-wide association analyses of MDD and related disease subtypes and endophenotypes. While monoamine signaling has preoccupied the bulk of scientific investigation to date, nontraditional gene candidates such as PCLO and GRM7 are now emerging and beginning to change the landscape for future human and animal research on depression.

Alternative splicing and extensive RNA editing of human TPH2 transcripts

Brain serotonin (5-HT) neurotransmission plays a key role in the regulation of mood and has been implicated in a variety of neuropsychiatric conditions. Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in the biosynthesis of 5-HT. Recently, we discovered a second TPH isoform (TPH2) in vertebrates, including man, which is predominantly expressed in brain, while the previously known TPH isoform (TPH1) is primarly a non-neuronal enzyme. Overwhelming evidence now points to TPH2 as a candidate gene for 5-HT-related psychiatric disorders. To assess the role of TPH2 gene variability in the etiology of psychiatric diseases we performed cDNA sequence analysis of TPH2 transcripts from human post mortem amygdala samples obtained from individuals with psychiatric disorders (drug abuse, schizophrenia, suicide) and controls. Here we show that TPH2 exists in two alternatively spliced variants in the coding region, denoted TPH2a and TPH2b. Moreover, we found evidence that the pre-mRNAs of both splice variants are dynamically RNA-edited in a mutually exclusive manner. Kinetic studies with cell lines expressing recombinant TPH2 variants revealed a higher activity of the novel TPH2B protein compared with the previously known TPH2A, whereas RNA editing was shown to inhibit the enzymatic activity of both TPH2 splice variants. Therefore, our results strongly suggest a complex fine-tuning of central nervous system 5-HT biosynthesis by TPH2 alternative splicing and RNA editing. Finally, we present molecular and large-scale linkage data evidencing that deregulated alternative splicing and RNA editing is involved in the etiology of psychiatric diseases, such as suicidal behaviour.

TPH2 is not a susceptibility gene for suicide in Japanese population

BACKGROUND

Serotonergic systems mediate a control of aggression and/or impulsivity in human and are suggested to be involved in suicidal behavior. The newly identified neuronal tryptophan hydroxylase isoform 2 (TPH2), the rate-limiting enzyme in serotonin synthesis, represents a prime candidate in numerous genetic association analyses of suicidal behavior; however, the results are still inconclusive. The discrepancy may result from the heterogeneity of pathogenesis of suicidal behavior and/or methodological mismatches. We, therefore, attempted to replicate the association of TPH2 gene with suicide using a case-control study of 234 completed suicides and 260 control subjects in Japanese population.

METHODS

We genotyped 15 tagging-single nucleotide polymorphisms (SNPs) including 4 SNPs, which were previously reported to be associated with suicidal behavior, using the TaqMan probe assays and the polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) method.

RESULTS

We found no significant differences in genotypic distributions (uncorrected p=0.06-0.98) or allelic frequencies (uncorrected p=0.09-0.95) of the fifteen SNPs between the completed suicides and control groups. Haplotypes constructed with these SNPs were also not associated with suicide (uncorrected p=0.03-0.96 and corrected p=0.20-1.00). Even when we took sex and suicidal methods (violent or non-violent) into account for the analyses, no significant differences in genotypic distributions, allelic/haplotypic frequencies were found in the two groups.

CONCLUSION

Our results suggest that the common SNPs and haplotypes of the TPH2 gene are unlikely to contribute to the genetic susceptibility to suicidal behavior in Japanese population.

Chronic citalopram administration causes a sustained suppression of serotonin synthesis in the mouse forebrain

BACKGROUND

Serotonin (5-HT) is a neurotransmitter with important roles in the regulation of neurobehavioral processes, particularly those regulating affect in humans. Drugs that potentiate serotonergic neurotransmission by selectively inhibiting the reuptake of serotonin (SSRIs) are widely used for the treatment of psychiatric disorders. Although the regulation of serotonin synthesis may be an factor in SSRI efficacy, the effect of chronic SSRI administration on 5-HT synthesis is not well understood. Here, we describe effects of chronic administration of the SSRI citalopram (CIT) on 5-HT synthesis and content in the mouse forebrain.

METHODOLOGY/PRINCIPAL FINDINGS

Citalopram was administered continuously to adult male C57BL/6J mice via osmotic minipump for 2 days, 14 days or 28 days. Plasma citalopram levels were found to be within the clinical range. 5-HT synthesis was assessed using the decarboxylase inhibition method. Citalopram administration caused a suppression of 5-HT synthesis at all time points. CIT treatment also caused a reduction in forebrain 5-HIAA content. Following chronic CIT treatment, forebrain 5-HT stores were more sensitive to the depleting effects of acute decarboxylase inhibition.

CONCLUSIONS/SIGNIFICANCE

Taken together, these results demonstrate that chronic citalopram administration causes a sustained suppression of serotonin synthesis in the mouse forebrain. Furthermore, our results indicate that chronic 5-HT reuptake inhibition renders 5-HT brain stores more sensitive to alterations in serotonin synthesis. These results suggest that the regulation of 5-HT synthesis warrants consideration in efforts to develop novel antidepressant strategies.

Genetic architecture of the human tryptophan hydroxylase 2 Gene: existence of neural isoforms and relevance for major depression

Impaired brain serotonin neurotransmission is a potential component of the diathesis of major depression. Tryptophan hydroxylase-2 (TPH2), is the rate limiting biosynthetic isoenzyme for serotonin that is preferentially expressed in the brain and a cause of impaired serotonin transmission. Here, we identify a novel TPH2 short isoform with truncated catalytic domain expressed in human brainstem, prefrontal cortex, hippocampus and amygdala. An exploratory study of 166 Caucasian subjects revealed association with major depression or suicide of a novel single nucleotide polymorphism (SNP) g.22879A>G located in exon 6 of this short isoform. This SNP and additional SNPs were discovered through a systematic characterization of the genetic architecture of the TPH2 gene for further genetic and functional investigations of its relationship to major depression and other psychopathology.

Elevated expression of tryptophan hydroxylase-2 mRNA at the neuronal level in the dorsal and median raphe nuclei of depressed suicides

Deficient levels of serotonin are associated with suicide and depression. Paradoxically, in the dorsal raphe nucleus (DRN) there are more serotonin neurons and more neuronal tryptophan hydroxylase-2 (TPH2) expression postmortem in depressed suicides. In this study, we sought to determine whether greater TPH2 expression in depressed suicides was the result of more TPH2 expression per neuron. In situ hybridization and computer-assisted image analysis were performed on tissue sections throughout the extent of the raphe nuclei at the level of silver grains per neuron to systematically quantify TPH2 neuronal expression. Depressed suicides have 26.5% more TPH2 grain density per neuron in the DRN compared with matched controls (P=0.04). The difference in grain density is greater at mid- and caudal anatomical levels across the rostrocaudal axis of the DRN. Densitometric analysis of TPH2 expression in the DRN subnuclei showed that higher expression levels were observed at posterior anatomical levels of depressed suicides (121% of control in the caudal subnucleus). Higher TPH2 expression in depressed suicides may explain more TPH2 protein and reflect a homeostatic response to deficient serotonin levels in the brains of depressed suicides. Localized changes in TPH2 expression in specific subnuclei of the DRN suggest that the serotonergic compensatory mechanism in depression and suicide is specifically regulated within the DRN and has implications for regions innervated by this subnucleus.

Glucocorticoid modulation of tryptophan hydroxylase-2 protein in raphe nuclei and 5-hydroxytryptophan concentrations in frontal cortex of C57/Bl6 mice

Considerable attention has focused on regulation of central tryptophan hydroxylase (TPH) activity and protein expression. At the time of these earlier studies, it was thought that there was a single central TPH isoform. However, with the recent identification of TPH2, it becomes important to distinguish between regulatory effects on the protein expression and activity of the two isoforms. We have generated a TPH2-specific polyclonal antiserum (TPH2-6361) to study regulation of TPH2 at the protein level and to examine the distribution of TPH2 expression in rodent and human brain. TPH2 immunoreactivity (IR) was detected throughout the raphe nuclei, in lateral hypothalamic nuclei and in the pineal body of rodent and human brain. In addition, a prominent TPH2-IR fiber network was found in the human median eminence. We recently reported that glucocorticoid treatment of C57/Bl6 mice for 4 days markedly decreased TPH2 messenger RNA levels in the raphe nuclei, whereas TPH1 mRNA was unaffected. The glucocorticoid-elicited inhibition of TPH2 gene expression was blocked by co-administration of the glucocorticoid receptor antagonist mifepristone (RU-486). Using TPH2-6361, we have extended these findings to show a dose-dependent decrease in raphe TPH2 protein levels in response to 4 days of treatment with dexamethasone; this effect was blocked by co-administration of mifepristone. Moreover, the glucocorticoid-elicited inhibition of TPH2 was functionally significant: serotonin synthesis was significantly reduced in the frontal cortex of glucocorticoid-treated mice, an effect that was blocked by mifepristone co-administration. This study provides further evidence for the glucocorticoid regulation of serotonin biosynthesis via inhibition of TPH2 expression, and suggest that elevated glucocorticoid levels may be relevant to the etiology of psychiatric diseases, such as depression, where hypothalamic-pituitary-adrenal axis dysregulation has been documented.

TPH2 and TPH1: association of variants and interactions with heroin addiction

The tryptophan hydroxylase 2 gene (TPH2) was resequenced at the 5' upstream, coding, and 3' downstream regions, including all 11 exons in 185 subjects. Twenty-three novel and 14 known variants were identified. In a cohort of 583 consecutively ascertained subjects, including normal volunteers and those with specific addictive diseases, six common TPH2 and one TPH1 variant were genotyped. Allele frequencies of three TPH2 variants and the TPH1 variant varied significantly among the four ethnic groups within the control subjects. Of these subjects, 385 who met heroin addiction or control criteria and were of Caucasian, African-American, or Hispanic ethnicity were examined for potential association with vulnerability to develop heroin addiction. At the two locus genotype level in Hispanics, the TPH1 rs1799913 variant was found to significantly interact with the TPH2 rs7963720 variant and heroin addiction (P=0.022), and with the TPH2 rs4290270 variant and heroin addiction (P=0.011). In the African-American group, a significant association of a specific TPH2 haplotype with heroin addiction also was found (SNPHAP, P=0.004; PHASE P=0.036).

Functional characterization of the human TPH2 5' regulatory region: untranslated region and polymorphisms modulate gene expression in vitro

Tryptophan hydroxylase-2 (TPH2) is a recently identified TPH isoform responsible for neuronal serotonin (5-HT) synthesis, and TPH2 polymorphisms are associated with a range of behavioral traits and psychiatric disorders. This study characterized cis-acting elements and three common polymorphisms (-703G/T, -473T/A, and 90A/G) in the 5' regulatory region of human TPH2 by using luciferase reporter assay, quantitative real-time PCR, and electrophoretic mobility shift assay (EMSA). The core promoter of human TPH2 was localized to the region between -107 and +7, and the segment of +8 to +53 within the 5'-UTR was found to exert a potent inhibitory effect on gene expression at both transcriptional and post-transcriptional levels. In both RN46A and HEK-293 cell lines, the TTA (-703T/-473T/90A) haplotype of the three polymorphisms showed the lowest gene expression compared with other haplotypes, and the -703G/T and -473T/A polymorphisms tended to exert a synergic effect on gene expression dependent upon the sequence of the 5'-UTR. In RN46A, the 90A/G polymorphism significantly increased luciferase activity and mRNA level irrespective of the other two polymorphisms, while in HEK-293 cells the effect of 90A/G was dependent on the alleles at loci -703 and -473. EMSA showed that all the three polymorphisms potentially alter DNA-protein interactions, while the 90A/G polymorphism predictably alters the 5'-UTR secondary structure of mRNA and influences RNA-protein interactions. In conclusion, our present study demonstrates that both the 5'-UTR and common polymorphisms (especially the 90A/G) in the 5' regulatory region of human TPH2 have a significant impact on gene expression.

Polymorphisms in the neuronal isoform of tryptophan hydroxylase 2 are associated with bipolar disorder in French Canadian pedigrees

OBJECTIVE

Tryptophan hydroxylase is the rate-limiting enzyme in the serotonin biosynthetic pathway and plays an important role in the regulation of serotonin levels. Recently, a brain-specific isoform, tryptophan hydroxylase 2 or n-tryptophan hydroxylase, has been discovered. Some studies reported genetic and functional associations between this isoform and bipolar disorder and/or major depressive disorder. The aim of this study was to investigate further association of genetic variants in French Canadian samples with bipolar disorders.

METHODS

Genetic variants in the tryptophan hydroxylase 2 gene were genotyped in a case-control sample consisting of 225 affected individuals (191 bipolar I and 34 bipolar II) and 221 controls and in a collection of extended pedigrees and trios from the same population 357 nuclear families (201 bipolar I, 64 bipolar II, 79 recurrent major depressive disorder).

RESULTS

We determined linkage disequilibrium structure in our isolated population and analyzed six tagged single nucleotide polymorphisms in the case-control sample. Whereas no single, single nucleotide polymorphism gave any significant result, a three single nucleotide polymorphism haplotype gave a global P=0.01. Family-based association showed significant association (P=0.004) of one polymorphism (rs4290270) with the major allele overtransmitted to affected offspring.

CONCLUSIONS

Case-control and family-based association studies further support the presence of a susceptibility locus for bipolar disorder in tryptophan hydroxylase 2 by showing statistically significant associations with both, single nucleotide polymorphism alone and haplotype of single nucleotide polymorphism markers.

Molecular genetics of bipolar disorder and depression

In this review, all papers relevant to the molecular genetics of bipolar disorder published from 2004 to the present (mid 2006) are reviewed, and major results on depression are summarized. Several candidate genes for schizophrenia may also be associated with bipolar disorder: G72, DISC1, NRG1, RGS4, NCAM1, DAO, GRM3, GRM4, GRIN2B, MLC1, SYNGR1, and SLC12A6. Of these, association with G72 may be most robust. However, G72 haplotypes and polymorphisms associated with bipolar disorder are not consistent with each other. The positional candidate approach showed an association between bipolar disorder and TRPM2 (21q22.3), GPR50 (Xq28), Citron (12q24), CHMP1.5 (18p11.2), GCHI (14q22-24), MLC1 (22q13), GABRA5 (15q11-q13), BCR (22q11), CUX2, FLJ32356 (12q23-q24), and NAPG (18p11). Studies that focused on mood disorder comorbid with somatic symptoms, suggested roles for the mitochondrial DNA (mtDNA) 3644 mutation and the POLG mutation. From gene expression analysis, PDLIM5, somatostatin, and the mtDNA 3243 mutation were found to be related to bipolar disorder. Whereas most previous positive findings were not supported by subsequent studies, DRD1 and IMPA2 have been implicated in follow-up studies. Several candidate genes in the circadian rhythm pathway, BmaL1, TIMELESS, and PERIOD3, are reported to be associated with bipolar disorder. Linkage studies show many new linkage loci. In depression, the previously reported positive finding of a gene-environmental interaction between HTTLPR (insertion/deletion polymorphism in the promoter of a serotonin transporter) and stress was not replicated. Although the role of the TPH2 mutation in depression had drawn attention previously, this has not been replicated either. Pharmacogenetic studies show a relationship between antidepressant response and HTR2A or FKBP5. New technologies for comprehensive genomic analysis have already been applied. HTTLPR and BDNF promoter polymorphisms are now found to be more complex than previously thought, and previous papers on these polymorphisms should be treated with caution. Finally, this report addresses some possible causes for the lack of replication in this field.

Tryptophan hydroxylase-2 gene polymorphisms in rhesus monkeys: association with hypothalamic-pituitary-adrenal axis function and in vitro gene expression

Tryptophan hydroxylase-2 (TPH2) is a newly identified second form of TPH responsible for serotonin synthesis in the brain and has been increasingly implicated as a contributor to the etiology of various psychiatric disorders. In this study, we have identified the constellation of polymorphisms in rhesus monkey TPH2 and investigated genotype/phenotype association as well as gene expression effects of specific polymorphisms. Genomic DNA was obtained from 247 rhesus monkeys, among which 24 had been previously examined for plasma cortisol level, dexamethasone suppression, and combined dexmethasone/ACTH challenge. Polymorphisms in all exons, splicing junctions and approximately 2 kb of the 5'-flanking region (5'-FR) of TPH2 were identified by sequencing. We identified 17 single nucleotide polymorphisms (SNPs) including two that are predictive of amino-acid change (25Pro>His and 75Gly>Ser, respectively), two mononucleotide repeats, one dinucleotide repeat, and one 159-bp insertion polymorphism. The 3'-UTR polymorphisms were significantly associated with hypothalamic-pituitary-adrenal (HPA) axis activity, especially 2051A>C, which was strikingly correlated with plasma cortisol level in the morning only (F=10.203, P=0.001). Luciferase reporter gene assays showed that the 3'-UTR polymorphisms and haplotypes had a profound effect on in vitro gene expression. Accordingly, these investigations revealed that polymorphisms in 3'-UTR of rhesus monkey TPH2 modulate HPA axis function, presumably by affecting levels of TPH2 expression.

Epistemological issues in omics and high-dimensional biology: give the people what they want

Gene expression microarrays have been the vanguard of new analytic approaches in high-dimensional biology. Draft sequences of several genomes coupled with new technologies allow study of the influences and responses of entire genomes rather than isolated genes. This has opened a new realm of highly dimensional biology where questions involve multiplicity at unprecedented scales: thousands of genetic polymorphisms, gene expression levels, protein measurements, genetic sequences, or any combination of these and their interactions. Such situations demand creative approaches to the processes of inference, estimation, prediction, classification, and study design. Although bench scientists intuitively grasp the need for flexibility in the inferential process, the elaboration of formal supporting statistical frameworks is just at the very start. Here, we will discuss some of the unique statistical challenges facing investigators studying high-dimensional biology, describe some approaches being developed by statistical scientists, and offer an epistemological framework for the validation of proffered statistical procedures. A key theme will be the challenge in providing methods that a statistician judges to be sound and a biologist finds informative. The shift from family-wise error rate control to false discovery rate estimation and to assessment of ranking and other forms of stability will be portrayed as illustrative of approaches to this challenge.

Major affective disorders and schizophrenia: a common molecular signature?

Psychiatric disorders, including affective disorders (AD) and schizophrenia (SZ) are among the most common disabling brain diseases in Western populations and result in high costs in terms of morbidity as well as mortality. Although their etiology and pathophysiology is largely unknown, family-, twin-, and adoption studies argue for a strong genetic determination of these disorders. These studies indicate that there is between 40 and 85% heritability for these disorders but point also to the importance of environmental factors. Therefore, any research strategy aiming at the identification of genes involved in the development of AD and SZ should account for the complex nature (multifactorial) of these disorders. During the last decade, molecular genetic studies have contributed a great deal to the identification of genetic factors involved in complex disorders. Here we provide a comprehensive review of the most promising genes for AD and SZ, and the methods and approaches that were used for their identification. Also, we discuss the current knowledge and hypotheses that have been formulated regarding the effect of variations on protein functioning as well as recent observations that point to common molecular mechanisms.