Evidence that a single nucleotide polymorphism in the promoter of the G protein receptor kinase 3 gene is associated with bipolar disorder

In a genome-wide linkage survey, we have previously shown evidence suggesting that the chromosome 22q12 region contains a susceptibility locus for bipolar disorder (BPD). Two independent family sets yielded lod scores suggestive of linkage at markers in this region near the gene G protein receptor kinase 3 (GRK3). GRK3 is an excellent candidate risk gene for BPD since GRK3 is expressed widely in the brain, and since GRKs play key roles in the homologous desensitization of G protein-coupled receptor signaling. We have also previously shown GRK3 expression to be induced by amphetamine in an animal model of mania using microarray-based expression profiling. To identify possible functional mutations in GRK3, we sequenced the putative promoter region, all 21 exons, and intronic sequence flanking each exon, in 14-22 individuals with BPD. We found six sequence variants in the 5'-UTR/promoter region, but no coding or obvious splice variants. Transmission disequilibrium analyses of one set of 153 families indicated that two of the 5'-UTR/promoter variants are associated with BPD in families of northern European Caucasian ancestry. A supportive trend towards association to one of these two variants (P-5) was then subsequently obtained in an independent sample of 237 families. In the combined sample, the P-5 variant had an estimated allele frequency of 3% in bipolar subjects, and displayed a transmission to non-transmission ratio of 26 : 7.7 (chi(2)=9.6, one-sided P value=0.0019). Altogether, these data support the hypothesis that a dysregulation in GRK3 expression alters signaling desensitization, and thereby predisposes to the development of BPD.

The unstable trinucleotide repeat story of major psychosis

New hopes for cloning susceptibility genes for schizophrenia and bipolar affective disorder followed the discovery of a novel type of DNA mutation, namely unstable DNA. One class of unstable DNA, trinucleotide repeat expansion, is the causal mutation in myotonic dystrophy, fragile X mental retardation, Huntington disease and a number of other rare Mendelian neurological disorders. This finding has led researchers in psychiatric genetics to search for unstable DNA sites as susceptibility factors for schizophrenia and bipolar affective disorder. Increased severity and decreased age at onset of disease in successive generations, known as genetic anticipation, was reported for undifferentiated psychiatric diseases and for myotonic dystrophy early in the twentieth century, but was initially dismissed as the consequence of ascertainment bias. Because unstable DNA was demonstrated to be a molecular substrate for genetic anticipation in the majority of trinucleotide repeat diseases including myotonic dystrophy, many recent studies looking for genetic anticipation have been performed for schizophrenia and bipolar affective disorder with surprisingly consistent positive results. These studies are reviewed, with particular emphasis placed on relevant sampling and statistical considerations, and concerns are raised regarding the interpretation of such studies. In parallel, molecular genetic investigations looking for evidence of trinucleotide repeat expansion in both schizophrenia and bipolar disorder are reviewed. Initial studies of genome-wide trinucleotide repeats using the repeat expansion detection technique suggested possible association of large CAG/CTG repeat tracts with schizophrenia and bipolar affective disorder. More recently, three loci have been identified that contain large, unstable CAG/CTG repeats that occur frequently in the population and seem to account for the majority of large products identified using the repeat expansion detection method. These repeats localize to an intron in transcription factor gene SEF2-1B at 18q21, a site named ERDA1 on 17q21 with no associated coding region, and the 3' end of a gene on 13q21, SCA8, that is believed to be responsible for a form of spinocerebellar ataxia. At present no strong evidence exists that large repeat alleles at either SEF2-1B or ERDA1 are involved in the etiology of schizophrenia or bipolar disorder. Preliminary evidence suggests that large repeat alleles at SCA8 that are non-penetrant for ataxia may be a susceptibility factor for major psychosis. A fourth, but much more infrequently unstable CAG/CTG repeat has been identified within the 5' untranslated region of the gene, MAB21L1, on 13q13. A fifth CAG/CTG repeat locus has been identified within the coding region of an ion transporter, KCNN3 (hSKCa3), on 1q21. Although neither large alleles nor instability have been observed at KCNN3, this repeat locus has been extensively analyzed in association and family studies of major psychosis, with conflicting findings. Studies of polyglutamine containing genes in major psychosis have also shown some intriguing results. These findings, reviewed here, suggest that, although a major role for unstable trinucleotides in psychosis is unlikely, involvement at a more modest level in a minority of cases cannot be excluded, and warrants further investigation.

5HT1Dbeta Receptor gene implicated in the pathogenesis of Obsessive-Compulsive Disorder: further evidence from a family-based association study

Obsessive-Compulsive Disorder (OCD) is a psychiatric condition with strong evidence for a genetic component and for the involvement of genes of the serotonin system. In a recent family-based association study we reported an association between the G allele of the G861C polymorphism of the 5HT1Dbeta receptor gene and OCD. The aim of the present study was to further investigate for the presence of linkage disequilibrium between each of two polymorphisms of the 5HT1Dbeta receptor gene and OCD in a larger sample of OCD families. In a total of 121 families the G861C and the T371G polymorphisms of the 5HT1Dbeta receptor gene were genotyped using standard protocols. The genotyping data were analyzed with a new extension of the Transmission Disequilibrium Test (FBAT). The phenotypes considered in the analyses were the diagnosis of OCD and two quantitative phenotypes related to the diagnosis and clinically relevant, ie, the age at onset and the severity of OCD symptoms. We confirmed the previously found preferential transmission of the G861 allele to the affected subjects (z = 2.262, P = 0.02). No significant association was found between the polymorphism and the quantitative phenotypes considered. These results represent a confirmation of our previous published study and thus, could have important implications for the role of the 5HT1Dbeta receptor gene in the pathogenesis and treatment of OCD. Further genetic investigations on this marker considering additional polymorphisms and other quantitative phenotypes related to OCD are warranted.

Dopamine D4 receptor and tyrosine hydroxylase genes in bipolar disorder: evidence for a role of DRD4

The involvement of the mesocorticolimbic dopamine system in behaviors that are compromised in patients with mood disorder has led to the investigation of dopamine system genes as candidates for bipolar disorder. In particular, the functional VNTRs in the exon III of the dopamine D4 (DRD4) and in intron I of the tyrosine hydroxylase (TH) genes have been investigated in numerous association studies that have produced contrasting results. Likewise, linkage studies in multiplex bipolar families have shown both positive and negative results for markers in close proximity to DRD4 and TH on 11p15.5. We performed a linkage disequilibrium analysis of the DRD4 and TH VNTRs in a sample of 145 nuclear families comprised of DSM-IV bipolar probands and their biological parents. An excess of transmissions and non transmissions was observed for the DRD4 4- and 2-repeat alleles respectively. The biased transmission showed a parent of origin effect (POE) since it was derived almost exclusively from the maternal meiosis (4-repeat allele maternally transmitted 40 times vs 20 times non-transmitted; chi(2) = 6.667; df = 1; P = 0.009; while paternally transmitted 26 times vs 21 times non-transmitted; chi(2) = 0.531; df = 1; P = 0.46). The analysis of TH did not reveal biased transmission of intron I VNTR alleles. Although replication of our study is necessary, the fact that DRD4 exhibit POE and is located on 11p15.5, in close proximity to a cluster of imprinted genes, suggests that genomic imprinting may be operating in bipolar disorder.

Identification of candidate genes for psychosis in rat models, and possible association between schizophrenia and the 14-3-3eta gene

Although the genetic contribution to schizophrenia is substantial, positive findings in whole-genome linkage scans have not been consistently replicated. We analyzed gene expression in various rat conditions to identify novel candidate genes for schizophrenia. Suppression subtraction hybridization (SSH), with polyA mRNA from temporal and frontal cortex of rats, was used to identify differentially expressed genes. Expression of mRNA was compared between adult Lewis and Fischer 344 (F344) rats, adult and postnatal day 6 (d6) F344, and adult F344 treated with haloperidol or control vehicle. These groups were chosen because each highlights a particular aspect of schizophrenia: differences in strain vulnerability to behavioral analogs of psychosis; factors that may relate to disease onset in relation to CNS development; and improvement of symptoms by haloperidol. The 14-3-3 gene family, as represented by 14-3-3gamma and 14-3-3zeta isoforms in the SSH study, and SNAP-25 were among the candidate genes. Genetic association between schizophrenia and the 14-3-3eta gene, positioned close to a genomic locus implicated in schizophrenia, and SNAP-25 genes was analyzed in 168 schizophrenia probands and their families. These findings address three different genes in the 14-3-3 family. We find a significant association with schizophrenia for two polymorphisms in the 14-3-3eta gene: a 7 bp variable number of tandem repeats in the 5' noncoding region (P=0.036, 1 df), and a 3' untranslated region SNP (753G/A) that is an RFLP visualized with Ava II (P=0.028). There was no significant genetic association with SNAP-25. The candidate genes identified may be of functional importance in the etiology, pathophysiology or treatment response of schizophrenia or psychotic symptoms. This is to our knowledge the first report of a significant association between the 14-3-3eta-chain gene and schizophrenia in a family-based sample, strengthening prior association reports in case-control studies and microarray gene expression studies.

Evidence that the N-methyl-D-aspartate subunit 1 receptor gene (GRIN1) confers susceptibility to bipolar disorder

There is evidence for the involvement of glutamatergic transmission in the pathogenesis of major psychoses. The two most commonly used mood stabilizers (ie lithium and valproate) have been found to act via the N-methyl-D-aspartate receptor (NMDAR), suggesting a specific role of NMDAR in the pathogenesis of bipolar disorder (BP). The key subunit of the NMDAR, named NMDA-1 receptor, is coded by a gene located on chromosome 9q34.3 (GRIN1). We tested for the presence of linkage disequilibrium between the GRIN1 (1001-G/C, 1970-A/G, and 6608-G/C polymorphisms) and BP. A total of 288 DSM-IV Bipolar I, Bipolar II, or schizoaffective disorder, manic type, probands with their living parents were studied. In all, 73 triads had heterozygous parents for the 1001-G/C polymorphism, 174 for the 1970-A/G, and 48 for the 6608-G/C. These triads were suitable for the final analyses, that is, the transmission disequilibrium test (TDT) and the haplotype-TDT. For the 1001-G/C and the 6608-G/C polymorphisms, we found a preferential transmission of the G allele to the affected individuals (chi(2)=4.765, df=1, P=0.030 and chi(2)= 8.395, df=1, P=0.004, respectively). The 1001G-1970A-6608A and the 1001G-1970A-6608G haplotypes showed the strongest association with BP (global chi(2)=14.12, df=4, P=0.007). If these results are replicated there could be important implications for the involvement of the GRIN1 in the pathogenesis of BP. The role of the gene variants in predicting the response to mood stabilizers in BP should also be investigated.

The serotonin 5-HT1B receptor gene and attention deficit hyperactivity disorder

Recent research has suggested that serotonin, in addition to dopamine, may be involved in the development of attention deficit hyperactivity disorder (ADHD). Serotonin regulates dopaminergic neurotransmission in some areas of the brain via several 5-HT receptors including 5-HT1B. Animal studies have suggested the involvement of the 5-HT1B receptors in locomotor behaviour. For these reasons, we hypothesized that the 5-HT1B receptor gene may be a good candidate for genetic studies of ADHD. We tested for linkage disequilibrium between the 5-HT1B G861C polymorphism and ADHD in 115 families using the transmission disequilibrium test (TDT). We found evidence for a trend towards excess transmission of the 861G allele (chi(2) = 2.91, P = 0.09) that when further analysed for parental allele transmissions exhibited significantly greater paternal transmission of the G allele (chi(2) = 4.80, P = 0.03) to the affected child. Although preliminary, results from this study provide additional evidence that serotonin genes may be important risk factors for the development of ADHD.

D1 receptor alleles predict PET metabolic correlates of clinical response to clozapine

A goal of pharmacogenetics is to clarify associations between allelic variation and risk factors in psychiatric illness. We report changes in regional brain metabolism based on dopamine alleles. Treatment-resistant schizophrenic subjects were positron emission tomography scanned with 18F-fluorodeoxyglucose after 5 weeks each of placebo and clozapine treatment. Significant regional brain metabolic effects were found for the D1 receptor genotypes (P < 0.05), adjusted for multiple comparisons. Metabolic decreases for the 2,2 genotype but not the 1,2 genotype were observed in all major sectors of the brain, with the exception of the ventral parts of the caudate and putamen. Frontal, temporal, parietal, and occipital neocortices showed decreased metabolism as did the cingulate juxta-allocortex and the parahippocampal allocortex. Decreases were also observed in the thalamus, amygdala, and cerebellum bilaterally. No significant metabolic differences by genotype were observed for D3, 5HT(2A), and 5HT(2C) polymorphisms. In terms of clinical response, the DRD1 2,2 genotype significantly improved with clozapine treatment, demonstrating a 30% decrease in the Brief Psychiatric Rating Scale positive symptoms in contrast to a 7% worsening for the 1,2 genotype (P < 0.05). In this preliminary study, brain metabolic and clinical response to clozapine are related to the D1 receptor genotype.

Polymorphism of the serotonin-2A receptor gene (HTR2A) associated with childhood attention deficit hyperactivity disorder (ADHD) in adult women with seasonal affective disorder

INTRODUCTION

Several lines of research point to a possible overlap between seasonal affective disorder (SAD) and attention deficit hyperactivity disorder (ADHD), particularly in females. There is also emerging evidence that variation of the 5-HT2A receptor gene (HTR2A) contributes to both SAD and ADHD. The current study investigated whether variation in HTR2A was associated with symptoms of childhood ADHD in adult women with SAD.

METHOD

Sixty-six women with SAD were administered the Wender-Utah Rating Scale (WURS), which retrospectively assesses childhood ADHD, as part of an ongoing genetic study of SAD. WURS scores were compared across the three genotypic groups defined by the T102C polymorphism of HT2RA.

RESULTS

Analysis of variance indicated a significant difference in mean 25-item WURS scores across the three genotypic groups (p = 0.035). Post-hoc tests revealed that the C/C genotypic group had a significantly higher mean score than both the T/T group and T/C group. Based on previously established WURS criteria, 38% of subjects with the C/C genotype, and none with the T/T genotype, had scores consistent with childhood ADHD.

LIMITATIONS

The current sample size is small, and childhood ADHD diagnoses were based on retrospective recall.

CONCLUSION

These preliminary results suggest a possible association between variation in HTR2A, childhood ADHD, and the later development of SAD in women.

Evidence for linkage disequilibrium between the alpha 7-nicotinic receptor gene (CHRNA7) locus and schizophrenia in Azorean families

Recent studies have suggested that the alpha 7-nicotinic receptor gene (CHRNA7) may play a role in the pathogenesis of schizophrenia. The alpha 7-nicotinic receptor gene (CHRNA7) is involved in P50 auditory sensory gating deficits, and the genomic locus for this gene lies in the chromosome 15q13-14 regions. The human gene is partially duplicated (exons 5-10) with four novel upstream exons. The marker D15S1360 has been shown to be significantly linked with the phenotype of abnormal P50 suppression in schizophrenia families. The marker L76630 is 3 kb in the 3' direction from the last exon of the CHRNA7 gene and is located in the duplicated region. The function of the two L76630 copies is unknown. We genotyped three polymorphic markers D15S1360, D15S165, and L76630 that are localized in a genomic fragment containing the CHRNA7 in 31 Azorean schizophrenia families/trios (including 41 schizophrenia individuals and 97 unaffected families members). An overall analysis utilizing the family-based association test revealed significant linkage disequilibrium between L76630 and schizophrenia (P = 0.0004). Using the extended transmission disequilibrium test and limiting the analysis to one triad per family, transmission disequilibrium of D15S1360 was near significance (P = 0.078). The 15q13 region overlaps with the location of two well-known genomically imprinted disorders: Angelman syndrome and Prader-Willi syndrome. Therefore, we investigated maternal and paternal meioses. We found significant transmission disequilibrium for D15S1360 through paternal transmission (P = 0.0006) in our schizophrenia families. The L76630 marker showed a significant disequilibrium in maternal transmissions (P = 0.028). No parent-of-origin effect was found in D15S165. Overall, our results suggest that the CHRNA7 may play a role in schizophrenia in these families. A parent of origin effect may be present and requires further study.

Dopamine system genes not linked to social phobia

Social phobia, particularly in its generalized form, has a genetic component in its etiology as suggested by positive twin studies and child temperament studies of social anxiety. Observations from functional imaging research suggest that dopamine function may be abnormal in the brains of patients with social phobia. Our investigation examined polymorphisms in the dopamine D2, D3 and D4 receptor genes, plus the dopamine transporter gene in a sample consisting of 17 multiplex social phobia families. We employed both parametric and non-parametric methods to test for linkage. Linkage was excluded for all loci under the broad diagnostic category. In the medium diagnostic category, the D3 receptor gene showed non-significant positive LOD scores (LOD = 0.62). We are able to clearly exclude a major effect for each of the four dopamine gene markers under the broad diagnosis of social phobia. Additional studies of dopamine system genes will be necessary to define clearly their role in social phobia.

Amphetamine, 3,4-methylenedioxymethamphetamine, lysergic acid diethylamide, and metabolites of the catecholamine neurotransmitters are agonists of a rat trace amine receptor

The trace amine para-tyramine is structurally and functionally related to the amphetamines and the biogenic amine neurotransmitters. It is currently thought that the biological activities elicited by trace amines such as p-tyramine and the psychostimulant amphetamines are manifestations of their ability to inhibit the clearance of extracellular transmitter and/or stimulate the efflux of transmitter from intracellular stores. Here we report the discovery and pharmacological characterization of a rat G protein-coupled receptor that stimulates the production of cAMP when exposed to the trace amines p-tyramine, beta-phenethylamine, tryptamine, and octopamine. An extensive pharmacological survey revealed that psychostimulant and hallucinogenic amphetamines, numerous ergoline derivatives, adrenergic ligands, and 3-methylated metabolites of the catecholamine neurotransmitters are also good agonists at the rat trace amine receptor 1 (rTAR1). These results suggest that the trace amines and catecholamine metabolites may serve as the endogenous ligands of a novel intercellular signaling system found widely throughout the vertebrate brain and periphery. Furthermore, the discovery that amphetamines, including 3,4-methylenedioxymethamphetamine (MDMA; "ecstasy"), are potent rTAR1 agonists suggests that the effects of these widely used drugs may be mediated in part by this receptor as well as their previously characterized targets, the neurotransmitter transporter proteins.

Genetic dissection of atypical antipsychotic-induced weight gain: novel preliminary data on the pharmacogenetic puzzle

Atypical antipsychotics such as clozapine represent a significant improvement over typical antipsychotics in the treatment of schizophrenia, particularly regarding extrapyramidal symptoms. Despite their benefits, use is limited by the occurrence of adverse reactions such as sedation and weight gain. This article provides a comprehensive review and discussion of obesity-related pathways and integrates these with the known mechanisms of atypical antipsychotic action to identify candidate molecules that may be disrupted during antipsychotic treatment. Novel preliminary data are presented to genetically dissect these obesity pathways and elucidate the genetic contribution of these candidate molecules to clozapine-induced weight gain. There is considerable variability among individuals with respect to the ability of clozapine to induce weight gain. Genetic predisposition to clozapine-induced weight gain has been suggested. Therefore, genetic variation in these candidate molecules may predict patient susceptibility to clozapine-induced weight gain. This hypothesis was tested for 10 genetic polymorphisms across 9 candidate genes, including the serotonin 2C, 2A, and 1A receptor genes (HTR2C/2A/1A); the histamine H1 and H2 receptor genes (H1R/H2R); the cytochrome P450 1A2 gene (CYPIA2); the beta3 and alpha,alpha-adrenergic receptor genes (ADRB3/ADRAIA); and tumor necrosis factor alpha (TNF-alpha). Prospective weight gain data were obtained for 80 patients with schizophrenia who completed a structured clozapine trial. Trends were observed for ADRB3, ADRA1A, TNF-alpha, and HTR2C; however, replication in larger, independent samples is required. Although in its infancy, psychiatric pharmacogenetics will in the future aid clinical practice in the prediction of response and side effects, such as antipsychotic-induced weight gain, and minimize the current "trial and error" approach to prescribing.

Altered IMPA2 gene expression and calcium homeostasis in bipolar disorder

Reduced inositol monophosphatase (IMPase) activity and elevated basal intracellular calcium levels ([Ca(2+)](B)) have been reported in B lymphoblast cell lines (BLCLs) from bipolar I affective disorder (BD-I) patients, which may reflect cellular endophenotypes of this disorder. As the PI cycle couples to intracellular Ca(2+) mobilization, these two putative endophenotypes may be related. Using an RT-PCR assay, mRNA levels were estimated for IMPA1 and 2 genes encoding human IMPase 1 and 2, respectively, in BLCLs phenotyped on [Ca(2+)](B), from patients with a DSM-IV diagnosis of BD-I (n = 12 per phenotype) and from age- and sex-matched healthy subjects (n = 12). IMPA2 mRNA levels were significantly lower in BLCLs from male BD-I patients with high [Ca(2+)](B) (n = 6) compared with healthy male subjects (n = 5) (-52%, P = 0.013), male BD-I patients with normal BLCL [Ca(2+)](B) (n = 8) (-42%, P = 0.003) and female BD-I patients with high [Ca(2+)](B) (n = 6) (-59%, P = 0.0004). A significant negative correlation was observed between IMPA2 mRNA levels and [Ca(2+)](B) in BLCLs from male (P = 0.046), but not female BD-I patients. Sex-dependent differences were also evident in postmortem temporal cortex IMPA2 mRNA levels which, in contrast to BLCLs, were significantly higher in male BD-I subjects compared with male controls (P = 0.025, n = 4/group). Collectively, these observations suggest a potential sex-dependent link between abnormalities in IMPA2 expression and calcium homeostasis in the pathophysiology of BD.

Altered TRPC7 gene expression in bipolar-I disorder

BACKGROUND

As altered storage-operated calcium (Ca(2+)) entry (SOCE) may affect Ca(2+) homeostasis in bipolar disorder (BD), we determined whether changes occur in the expression of TRPC7 and SERCA2s, proteins implicated or known to be involved in SOCE, in B lymphoblast cell lines (BLCLs) from BD-I patients and comparison subjects.

METHODS

mRNA levels were determined in BLCL lysates from BD-I, BD-II, and major depressive disorder patients, and healthy subjects by comparative reverse transcriptase-polymerase chain reaction, and BLCL basal intracellular Ca(2+) concentration ([Ca(2+)]B) was determined by ratiometric spectrophotometry using Fura-2, in aliquots of the same cell lines, at 13-16 passages in culture.

RESULTS

TRPC7 mRNA levels were significantly lower in BLCLs from BD-I patients with high BLCL [Ca(2+)]B compared with those showing normal [Ca(2+)]B (-33%, p =.017) and with BD-II patients (-48%, p =.003), major depressive disorder patients (-47%, p =.049) and healthy subjects (-33%, p =.038). [Ca(2+)]B also correlated inversely with TRPC7 mRNA levels in BLCLs from the BD-I group as a whole (r = -.35, p =.027).

CONCLUSIONS

Reduced TRPC7 gene expression may be a trait associated with pathophysiological disturbances of Ca(2+) homeostasis in a subgroup of BD-I patients.

Polymorphism of the serotonin 5-HT1B receptor gene (HTR1B) associated with minimum lifetime body mass index in women with bulimia nervosa

BACKGROUND

Preclinical research has shown that the serotonin-1B receptor has important modulatory effects on feeding behavior and thus body weight. In the current study, we examined whether genetic variation of the serotonin-1B receptor was associated with minimum and maximum lifetime body mass indices (BMIs) in a sample of women with bulimia nervosa (BN).

METHODS

Ninety-eight women with BN were genotyped based on the G861C polymorphism of the serotonin-1B receptor gene (HTR1B). Minimum and maximum lifetime BMIs were compared across the three genotypic groups using analysis of variance.

RESULTS

There was a highly significant difference in minimum lifetime BMI across the three genotypic groups (p =.001). Both the G/C and C/C genotypes were associated with significantly lower minimum lifetime BMIs than was the G/G genotype. Maximum lifetime BMI was not significantly different across groups. These results were not attributable to different lifetime rates of anorexia nervosa across the three genotypic groups.

CONCLUSIONS

These preliminary findings suggest a possible association between HTR1B genetic polymorphism and minimum lifetime BMI in women with BN. These findings may shed light on why, in response to dieting, some BN patients achieve lower BMIs, whereas others have a natural limitation to their weight loss. Pending replication in a larger sample, these findings point to a possible genetic factor of fundamental importance to the BN population.

The 5HT1Dbeta receptor gene in bipolar disorder: a family-based association study

The serotonin (5HT) receptor genes are considered good candidates for Major Depression (MD), Bipolar Disorder (BP), and Obsessive-Compulsive Disorder (OCD). The 5HT1Dbeta receptor gene has at least three polymorphisms known: G861C, T-261G, and the functional T371G (Phe-124-Cys). The aim of this study was to investigate for the presence of linkage disequilibrium between the 5HT1Dbeta receptor gene and BP. Two hundred and ninety probands with DSM-IV BPI, BPII, or Schizoaffective Disorder (Bipolar type) with their living parents were recruited. Genotyping data for the G861C and T371G polymorphisms were analyzed using the Transmission Disequilibrium Test (TDT). One hundred and sixty triads were informative for the TDT on the G861C polymorphism, which showed no preferential transmission of either allele (chi-square = 0.438, df = 1, p =.508). Only four triads were suitable for the analysis on the T371G variant, with the T allele transmitted once and the G allele transmitted four times to the affected. These findings validate further the results of pharmacological studies excluding a direct involvement of the 5HT1Dbeta receptor in the pathogenesis of BP. Further investigations combining genetic and pharmacological strategies are warranted.

CYP1A2 activity as measured by a caffeine test predicts clozapine and active metabolite steady-state concentrationin patients with schizophrenia

Clozapine is an atypical antipsychotic drug and displays efficacy in 30% to 60% of patients with schizophrenia who do not respond to traditional antipsychotics. A clozapine concentration greater than 1,150 nmol/L increases the probability of antipsychotic efficacy. However, plasma clozapine concentration can vary more than 45-fold during long-term treatment. The aim of this study was to assess the contribution of CYP1A2 to variability in steady-state concentration of clozapine and its active metabolite norclozapine. Patients with schizophrenia or schizoaffective disorder were prospectively monitored during clozapine treatment (N = 18). The in vivo CYP1A2 activity was measured using the caffeine metabolic ratio (CMR) in overnight urine. Trough plasma samples were drawn after at least 5 days of treatment with a constant regimen of clozapine. A significant negative association was found between the CMR and the dose-corrected clozapine (r(s) = -0.87,p < 0.01) and norclozapine (r(s) = -0.76,p < 0.01) concentrations. Nonsmokers displayed a higher clozapine (3.2-fold) and norclozapine (2.3-fold) concentration than smokers (p < 0.05). Furthermore, there was marked person-to-person variation in CYP1A2 activity during multiple-dose clozapine treatment (coefficient of variation = 60%). Age, weight, serum creatinine, and grapefruit juice consumption did not significantly contribute to variability in clozapine and norclozapine concentration (p > 0.05). In conclusion, CYP1A2 is one of the important contributors to disposition of clozapine during multiple-dose treatment. Although further in vitro experiments are necessary, the precise metabolic pathways catalyzed by CYP1A2 seem to be subsequent to the formation of norclozapine, hitherto less recognized quantitatively important alternate disposition routes, or both. From a clinical perspective, an environmentally induced or constitutively high CYP1A2 expression can lead to a decrease in steady-state concentration of clozapine as well as its active metabolite norclozapine. Thus, interindividual variability in CYP1A2 activity may potentially explain treatment resistance to clozapine in some patients. CYP1A2 phenotyping with a simple caffeine test may contribute to individualization of clozapine dosage and differentiate between treat ment noncompliance and high CYP1A2 activity.

The role of serotonin transporter protein gene in antidepressant-induced mania in bipolar disorder: preliminary findings

BACKGROUND

The occurrence of mania during antidepressant treatment is a key issue in the clinical management of bipolar disorder (BP). The serotonin transporter (5-HTT) is the selective site of action of most proserotonergic compounds used to treat bipolar depression. The 5-HTT gene (SLC6A4) has 2 known polymorphisms. The aim of this study was to investigate the role of the SLC6A4 variants in the pathogenesis of antidepressant-induced mania in BP.

METHODS

Twenty-seven patients with a DSM-IV diagnosis of BP I or II, with at least 1 manic or hypomanic episode induced by treatment with proserotonergic antidepressants (IM+ group), were compared with 29 unrelated, matched patients with a diagnosis of BP I or II, who had been exposed to proserotonergic antidepressants without development of manic or hypomanic symptoms (IM- group). The 2 known polymorphisms of the SLC6A4 were genotyped, and allelic and genotypic association analyses were performed.

RESULTS

With respect to the polymorphism in the promoter region (5HTTLPR), IM+ patients had an excess of the short allele (n = 34 [63%]) compared with IM- patients (n = 17 [29%]) (chi(2)(1), 12.77; P <.001). The genotypic association analysis showed a higher rate of homozygosity for the short variant in the IM+ group (n = 10 [37%]) than in the IM- group (n = 2 [7%]) and a lower rate of homozygosity for the long variant in the IM+ group (n = 3 [11%]) compared with the IM- group (n = 14 [48%]) (chi(2)(2), 12.43; P =.002). No associations were found for the polymorphism involving a variable number of tandem repeats.

CONCLUSION

If these results are replicated, the 5HTTLPR polymorphism may become an important predictor of abnormal response to medication in patients with BP.

Attention-deficit hyperactivity disorder and the adrenergic receptors alpha 1C and alpha 2C

The adrenergic system has been hypothesized to be involved in the etiology of attention-deficit hyperactivity disorder (ADHD) based on pharmacological interventions and animal models. Noradrenergic neurons are implicated in the modulation of vigilance, improvement of visual attention, initiation of adaptive response, learning and memory. In this study we tested the genes for two adrenergic receptors, alpha 1C (ADRA1C) located on chromosome 8p11.2, and alpha 2C (ADRA2C) located on chromosome 4p16, as genetic susceptibility factors in ADHD. For the adrenergic receptor alpha 1C we used a C to T polymorphism that results in a change of Cys to Arg at codon 492 for the linkage study. For the adrenergic receptor alpha 2C gene we examined a dinucleotide repeat polymorphism located approximately 6 kb from the gene. We examined these polymorphisms in a sample of 103 families ascertained through an ADHD proband. Using the transmission disequilibrium test, we did not observe biased transmission of any of the alleles of these polymorphisms. We conclude that the alleles at the polymorphisms tested in these two genes are not linked to the ADHD phenotype in this sample of families.

Linkage study of the alpha2A adrenergic receptor in attention-deficit hyperactivity disorder families

Attention-deficit hyperactivity disorder (ADHD) is a common childhood psychiatric disorder, characterized by marked and pervasive inattention, hyperactivity, and impulsiveness. An alteration in the expression or function of the adrenergic system has been suggested to be involved in ADHD based on animal models, pharmacological interventions, and the neural circuitry of attentional processes. The efficacy of clonidine in reducing disruptive behaviors in some children with ADHD argues for a causal role of the adrenergic system and more specifically for the alpha2A receptors as clonidine is an alpha2A agonist that inhibits release of noradrenaline into the synapse. In animal studies, alpha2A receptor agonists have also been shown to improve performance on working memory tasks under distracting conditions, indicating that these receptors function in the regulation of attention. We examined the possibility that the gene for the alpha2A adrenergic receptor (ADRA2A) is linked to ADHD by testing a polymorphism located in the promoter region of the ADRA2A gene in a sample of 94 nuclear families with an ADHD proband. We found no evidence for linkage of the ADRA2A gene with ADHD, using the transmission disequilibrium test in this set of families.

Lack of association between serotonin-2A receptor gene (HTR2A) polymorphisms and tardive dyskinesia in schizophrenia

Tardive dyskinesia (TD) is a disabling neurological side effect associated with long-term treatment with typical antipsychotics. Family studies and animal models lend evidence for hereditary predisposition to TD. The newer atypical antipsychotics pose a minimal risk for TD which is in part attributed to their ability to block the serotonin-2A (5-HT(2A)) receptor. 5-HT(2A) receptors were also identified in the basal ganglia; a brain region that plays a critical role in antipsychotic-induced movement disorders. We tested the significance of variation in the 5-HT(2A) receptor gene (HTR2A) in relation to the TD phenotype. Three polymorphisms in HTR2A, one silent (C102T), one that alters the amino acid sequence (his452tyr) and one in the promoter region (A-1437G) were investigated in 136 patients refractory or intolerant to treatment with typical antipsychotics and with a DSM-IIIR diagnosis of schizophrenia. We did not find any significant difference in allele, genotype or haplotype frequencies of polymorphisms in HTR2A among patients with or without TD (P > 0.05). Further analysis using the ANCOVA statistic with a continuous measure of the TD phenotype (Abnormal Involuntary Movement Scale (AIMS) score) found that the AIMS scores were not significantly influenced by HTR2A polymorphisms, despite controlling for potential confounders such as age, gender and ethnicity (P > 0.05). Theoretically, central serotonergic function can be subject to genetic control at various other mechanistic levels including the rate of serotonin synthesis (tryptophane hydroxylase gene), release, reuptake (serotonin transporter gene) and degradation (monoamine oxidase gene). Analyses of these other serotonergic genes are indicated. In summary, polymorphisms in HTR2A do not appear to influence the risk for TD. Further studies evaluating in tandem multiple candidate genes relevant for the serotonergic system are warranted to dissect the genetic basis of the complex TD phenotype.

Haplotype study of three polymorphisms at the dopamine transporter locus confirm linkage to attention-deficit/hyperactivity disorder

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is often treated using methylphenidate, a psychostimulant that inhibits the dopamine transporter. This led E.H. Cook and colleagues to consider the dopamine transporter locus (DAT1) as a primary candidate gene for ADHD. That group reported a significant association between ADHD and the 480-base pair (bp) allele of the variable number of tandem repeats (VNTR) polymorphism located in the 3' untranslated region of the DAT1 gene. This association was later replicated in additional studies.

METHODS

The DAT1 gene has additional common polymorphisms in intron 9 and exon 9. We investigated the possibility of linkage of DAT1 and ADHD using the VNTR polymorphism and two additional common polymorphisms in 102 nuclear families with an ADHD proband. Using the transmission disequilibrium test, we examined the transmission of the alleles of each of these polymorphisms, as well as the haplotypes of the polymorphisms.

RESULTS

We did not observe significant evidence for the biased transmission of the alleles of either the VNTR or the additional two polymorphisms when examined individually, although there was a trend for the biased transmission of the 480-bp allele of the VNTR. When we examined the haplotypes of the three polymorphisms we found significant evidence for biased transmission of one of the haplotypes containing the 480-bp VNTR allele. We also genotyped six additional DNA sequence variants of the DAT1 gene. However, these variants were not sufficiently polymorphic in our sample to be informative. Two of the DNA variants that result in an amino acid change, Ala559Val and Glu602Gly, were not observed in our sample.

CONCLUSIONS

Our results support previous findings of an association between the DAT1 gene and ADHD.