Transmission disequilibrium analysis of a triplet repeat within the hKCa3 gene using family trios with schizophrenia

Possible association of CAG repeat polymorphism in KCNN3 encoding the potassium channel SK3 with oxaliplatin-induced neurotoxicity

INTRODUCTION

Data suggest a role of the potassium channel SK3 (KCNN3 gene) in oxaliplatin-induced neurotoxicity (OIN). Length variations in the polymorphic CAG repeat of the KCNN3 gene may be associated with the risk of OIN.

MATERIALS AND METHODS

We performed patch-clamp experiments on HEK293 cell lines, expressing SK3 channel isoforms with short (11) or long (24) CAG repetitions, to measure intracellular calcium concentrations to test the effects of oxaliplatin on current density. A retrospective study was carried out on patients with colorectal cancer who had received oxaliplatin-based chemotherapy. DNA for KCNN3 genotyping was extracted from leukocytes. The region containing the CAG repeats was amplified by PCR and the products separated by capillary electrophoresis for length analysis. The patients were divided into three groups depending on whether they carried two short alleles, one short allele and one long allele, or two long alleles. The primary endpoint was the onset of grade 2 or 3 neuropathy to oxaliplatin.

RESULTS

There was no difference in current density, but oxaliplatin induced a differential effect on apamin-sensitive current density between the two isoforms expressed in the HEK cell lines. There was a significant reduction of store-operated calcium entry into cells expressing the short and more active isoform only after high concentration of oxaliplatin exposition. Eighty-six patients were included in the clinical study. There was no significant association between OIN and KCNN3 polymorphism for the three groups.

CONCLUSION

We observed a slight association between OIN and CAG repeat polymorphisms of the KCNN3 gene in a preclinical model, but not a clinical study.

Ion channels and schizophrenia: a gene set-based analytic approach to GWAS data for biological hypothesis testing

Schizophrenia is a complex genetic disorder. Gene set-based analytic (GSA) methods have been widely applied for exploratory analyses of large, high-throughput datasets, but less commonly employed for biological hypothesis testing. Our primary hypothesis is that variation in ion channel genes contribute to the genetic susceptibility to schizophrenia. We applied Exploratory Visual Analysis (EVA), one GSA application, to analyze European-American (EA) and African-American (AA) schizophrenia genome-wide association study datasets for statistical enrichment of ion channel gene sets, comparing GSA results derived under three SNP-to-gene mapping strategies: (1) GENIC; (2) 500-Kb; (3) 2.5-Mb and three complimentary SNP-to-gene statistical reduction methods: (1) minimum p value (pMIN); (2) a novel method, proportion of SNPs per Gene with p values below a pre-defined α-threshold (PROP); and (3) the truncated product method (TPM). In the EA analyses, ion channel gene set(s) were enriched under all mapping and statistical approaches. In the AA analysis, ion channel gene set(s) were significantly enriched under pMIN for all mapping strategies and under PROP for broader mapping strategies. Less extensive enrichment in the AA sample may reflect true ethnic differences in susceptibility, sampling or case ascertainment differences, or higher dimensionality relative to sample size of the AA data. More consistent findings under broader mapping strategies may reflect enhanced power due to increased SNP inclusion, enhanced capture of effects over extended haplotypes or significant contributions from regulatory regions. While extensive pMIN findings may reflect gene size bias, the extent and significance of PROP and TPM findings suggest that common variation at ion channel genes may capture some of the heritability of schizophrenia.

Molecular and cellular basis of small--and intermediate-conductance, calcium-activated potassium channel function in the brain

Small conductance calcium-activated potassium (SK or K_Ca2) channels link intracellular calcium transients to membrane potential changes. SK channel subtypes present different pharmacology and distribution in the nervous system. The selective blocker apamin, SK enhancers and mice lacking specific SK channel subunits have revealed multifaceted functions of these channels in neurons, glia and cerebral blood vessels. SK channels regulate neuronal firing by contributing to the afterhyperpolarization following action potentials and mediating I_AHP, and partake in a calcium-mediated feedback loop with NMDA receptors, controlling the threshold for induction of hippocampal long-term potentiation. The function of distinct SK channel subtypes in different neurons often results from their specific coupling to different calcium sources. The prominent role of SK channels in the modulation of excitability and synaptic function of limbic, dopaminergic and cerebellar neurons hints at their possible involvement in neuronal dysfunction, either as part of the causal mechanism or as potential therapeutic targets.

CAG repeat polymorphism within the KCNN3 gene is a significant contributor to susceptibility to anorexia nervosa: a case-control study of female patients and several ethnic groups in the Israeli Jewish population

The human small-conductance Ca(2+)-activated potassium channel gene KCNN3 has been involved in mechanisms underlying neuronal function and plasticity. A multiallelic CAG repeat polymorphism within the KCNN3 has been associated with schizophrenia and bipolar disorder. We have previously reported in a family-based study that longer CAG repeats are preferentially transmitted to patients with anorexia nervosa (AN). The present study extends the analysis of KCNN3 allele distribution to a larger series of AN female patients and control groups, incorporating information on ethnicity and co-morbidities associated with AN. The data analysis is presented while considering separately the two alleles of each individual, namely a minor (shorter) and a major (longer) allele. This study has found that the KCNN3 allele distribution in the general Israeli population does not differ significantly in at least four Jewish ethnic groups of Ashkenazi, North African, Iraqi, and Yemenite origin. These have been used as control groups in a matched case-control analysis that has demonstrated a significant over-representation of KCNN3 alleles with longer CAG repeats among AN patients (P < 0.001 for the major allele and P = 0.035 for allele sum). Under dichotomization, a significantly higher prevalence of the L allele (>19 repeats) has been observed among AN patients (P < 0.001). While considering AN and co-morbid phenotypes, a tendency towards longer (L) alleles has been observed in the subset of patients with obsessive-compulsive disorder (OCD) co-morbidity. These findings further implicate KCNN3 as a significant contributor to predisposition to AN.

The molecular genetics of schizophrenia: new findings promise new insights

The high heritability of schizophrenia has stimulated much work aimed at identifying susceptibility genes using positional genetics. However, difficulties in obtaining clear replicated linkages have led to the scepticism that such approaches would ever be successful. Fortunately, there are now signs of real progress. Several strong and well-established linkages have emerged. Three of the best-supported regions are 6p24-22, 1q21-22 and 13q32-34. In these cases, single studies achieved genome-wide significance at P<0.05 and suggestive positive findings have also been reported in other samples. The other promising regions include 8p21-22, 6q21-25, 22q11-12, 5q21-q33, 10p15-p11 and 1q42. The study of chromosomal abnormalities in schizophrenia has also added to the evidence for susceptibility loci at 22q11 and 1q42. Recently, evidence implicating individual genes within some of the linked regions has been reported and more importantly replicated. The weight of evidence now favours NRG1 and DTNBP1 as susceptibility loci, though work remains before we understand precisely how genetic variation at each locus confers susceptibility and protection. The evidence for catechol-O-methyl transferase, RGS4 and G72 is promising but not yet persuasive. While further replications remain the top priority, the respective contributions of each gene, relationships with aspects of the phenotype, the possibility of epistatic interactions between genes and functional interactions between the gene products will all need investigation. The ability of positional genetics to implicate novel genes and pathways will open up new vistas for neurobiological research, and all the signs are that it is now poised to deliver crucial insights into the nature of schizophrenia.

Association study of CAG repeats in the KCNN3 gene in Israeli patients with major psychosis

OBJECTIVES

Several studies reported contradictory findings regarding the association of major psychosis with CAG repeats in the KCNN3 gene. We investigated the contribution of the CAG repeat at the KCNN3 gene, localized to chromosome 1q21.3, to the genetic susceptibility for schizophrenia, schizoaffective and bipolar disorders.

METHODS

Analysis of the number of CAG repeats and the differences in allele length were performed for Israeli Ashkenazi Jews, non-Ashkenazi Jews, and Arabs diagnosed with major psychosis (n=181) versus matched ethnic controls (n=207).

RESULTS

We found no significant difference in the number of CAG repeats between the entire sample of patients and controls. However, an analysis of the differences of allele length revealed a significantly greater number of patients with identical allele length (43.1%) when compared with normal controls (30.4%). Furthermore, an earlier age of non-paranoid schizophrenia onset was found associated with differences in allele sizes. There were no significant differences in the number of CAG repeats and the differences in allele length when subjects were grouped according to gender, ethnic origins of their parents, family history, and diagnostic groups.

CONCLUSIONS

Our results support the hypothesis that a contribution of the KCNN3 gene to genetic susceptibility to major psychosis and their phenotypic polymorphism may be related to the difference of allele length rather than to the number of CAG repeats.

CAG-repeat length in exon 1 of KCNN3 does not influence risk for schizophrenia or bipolar disorder: a meta-analysis of association studies

Schizophrenia and bipolar disorder both show some evidence for genetic anticipation. In addition, significant expansion of anonymous CAG repeats throughout the genome has been detected in both of these disorders. The gene KCNN3, which codes for a small/intermediate conductance, calcium-regulated potassium channel, contains a highly polymorphic CAG-repeat array in exon 1. Initial evidence for association of both schizophrenia and bipolar disorder with increased CAG-repeat length of KCNN3 has not been consistently replicated. In the present study, we performed several meta-analyses to evaluate the pooled evidence for association with CAG-repeat length of KCNN3 derived from case-control and family-based studies of both disorders. Each group of studies was analyzed under two models, including a test for direct association with repeat length, and a test for association with dichotomized repeat-length groups. No evidence for a linear relationship between disease risk and repeat length was observed, as all pooled odds ratios approximated 1.0. Results of dichotomized allele-group analyses were more variable, especially for schizophrenia, where case-control studies found a significant association with longer repeats but family-based studies implicated shorter alleles. The results of these meta-analyses demonstrate that the risks for both schizophrenia and bipolar disorder are largely, if not entirely, independent of CAG-repeat length in exon 1 of KCNN3. This study cannot exclude the possibility that some aspect of this polymorphism, such as repeat-length disparity in heterozygotes, influences risk for these disorders. Further, it remains unknown if this polymorphism, or one in linkage disequilibrium with it, contributes to some distinct feature of the disorder, such as symptom severity or anticipation.

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.

Linkage and associated studies of schizophrenia

Genetic epidemiology has provided consistent evidence over many years that schizophrenia has a genetic component, and that this genetic component is complex, polygenic, and involves epistatic interaction between loci. Molecular genetics studies have, however, so far failed to identify any DNA variant that can be demonstrated to contribute to either liability to schizophrenia or to any identifiable part of the underlying pathology. Replication studies of positive findings have been difficult to interpret for a variety of reasons. First, few have reproduced the initial findings, which may be due either to random variation between two samples in the genetic inputs involved, or to a lack of power to replicate an effect at a given alpha level. Where positive data have been found in replication studies, the positioning of the locus has been unreliable, leading no closer to positional cloning of genes involved. However, an assessment of all the linkage studies performed over the past ten years does suggest a number of regions where positive results are found numerous times. These include regions on chromosomes 1, 2, 4, 5, 6, 7, 8, 9, 10, 13, 15, 18, 22 and the X. All of these data are critically reviewed and their locations compared. Reasons for the difficulty in obtaining consistent results and possible strategies for overcoming them are discussed. Am. J. Med. Genet. (Semin. Med. Genet.) 97:23-44, 2000.

Linkage of schizophrenia with chromosome 1q loci in Taiwanese families

A positive linkage of schizophrenia with chromosome 1q loci has been reported in Caucasian patients. This study was designed to evaluate the linkage of schizophrenia with markers of the 1q22-44 region in 52 Taiwanese families with at least two affected siblings. In the region 1q22-31 (17.8 cM), marker D1S1679 had a maximal proportion (0.57, P=0.03) of shared identity by descent (IBD) under a narrow phenotype (DSM-IV schizophrenia only). In the region 1q42-44 (26.8 cM), the marker D1S251, located near the breakpoint of a balanced translocation t (1;11) (q42.1;q14.3) segregated with schizophrenia, and also near the neurodevelopment-related 'Disrupted in Schizophrenia 1' gene, had a maximum NPL score of 1.73 (P=0.03) under the narrow phenotype model and 2.18 (P=0.01) under the broad phenotype model comprised of schizophrenia, schizoaffective disorder, and other nonaffective psychotic disorders as defined by DSM-IV criteria. The marker D1S2836 also had a maximal proportion (0.57, P=0.05) of shared IBD under the broad model. These findings may provide guidance for positional cloning studies on candidate genes in the 1q22-31 and 1q41-44 regions.

An association of CAG repeats at the KCNN3 locus with symptom dimensions of schizophrenia

BACKGROUND

In 1999 Cardno et al reported that long CAG repeats in the calcium-activated potassium channel gene hSKCa3/KCNN3 are associated with higher negative symptom dimension scores in schizophrenia patients. There has been no attempt to replicate the results. In this study, we investigated whether a symptom polymorphism of schizophrenia is associated with both the CAG repeat numbers and the difference in allele sizes.

METHODS

We tested the association of CAG repeats with symptom models of schizophrenia in 117 unrelated Jewish patients. A multivariate analysis (MANOVA) of two models of schizophrenia with the repeat distribution and the difference in allele sizes was performed.

RESULTS

We found a significant positive association of the number of CAG repeats with negative syndrome, anergia, activation, and paranoid symptoms. In addition, nonparanoid schizophrenia patients who had differences in allele sizes were characterized by earlier onset of illness.

CONCLUSIONS

The study supports the hypothesis that the combined effect of long CAG repeats and the differences in allele sizes contribute to symptom expression of schizophrenia, particularly on the anergia-activation-paranoid axis.

The French concept of "psychose hallucinatoire chronique" -a preliminary form of schizophrenia? The role of late-life psychosis in the anticipation hypothesis of schizophrenia

The distinction between schizophrenia and chronic delusional syndromes (including the French concept of “psychose hallucinatoire chronique” [PHC] or chronic psychotic hallucinations, paraphrenia, and late paraphrenia) is currently used in various European countries, although there are no international criteria for chronic and bizarre delusions. The French concept of PHC is characterized by late-onset psychosis, predominantly in females, with rich and frequent hallucinations, but almost no dissociative features or negative symptoms. PHC and late-onset schizophrenia may have risk factors in common, which may help differentiate these disorders from young-onset schizophrenia, especially with regard to the potential role of (i) the estradiol hypothesis; (ii) the impact of sensory deficit; (Hi) putative specific brain abnormalities; or (iv) specific genetic mutations. In accordance with this hypothesis, and taking into account the familial aggregation analyses of PHC, here we evaluate the possibility that PHC represents a less severe form of schizophrenia, which would partly explain the “Sherman paradox” also observed in schizophrenia. The Sherman paradox describes the fact that multiplex families frequently have only one affected ascendant, meaning that an isolated sporadic case is at the origin of a highly loaded family. We thus propose that if unstable mutations are involved in the risk for schizophrenia, then PHC might represent a moderate disorder belonging to the schizophrenia spectrum phenotype.

Lack of association between the hKCa3 gene and Japanese schizophrenia patients

Several researchers have suggested an association between large numbers of CAG repeats in the hKCa3 gene and schizophrenia. However, these reports remain inconclusive and require further investigation. We tried to replicate these results in 112 Japanese schizophrenia patients and 102 control subjects of highly matched age and sex by applying an allele dichotomization model. No association was found. The overall distributions of allele frequencies were not significantly different between schizophrenic patients and normal control subjects. In addition, we tested the association between the size of the CAG repeats and the scores on three dimensions (positive and negative symptoms, and disorganization), but no significant results were obtained. Our results do not support the involvement of the hKCa3 gene in schizophrenia, at least in the Japanese population.

Genetic basis of schizophrenia: trinucleotide repeats. An update

1. Recent developments in technologies permit systematic screening of the entire human genome as a strategy for identification of susceptibility genes of small effect that influence risk to complex traits, like schizophrenia (Schz), inflammatory bowel disease, bipolar affective disorder (BPAD) etc. 2. Schizophrenia is known to have a high heritability and a complex inheritance pattern. Several studies provide evidence that both genes and environment play a role in the etiology of schizophrenia. Linkage studies have observed racial and sex bias in the genetic constitution of schizophrenia. Schizophrenia also manifests clinical anticipation and genomic imprinting. 3. "Dynamic mutations" or "tandem repeat expansions" in DNA, explain a number of observations associated with clinical anticipation and genomic imprinting. In patient populations, the repeat expands well beyond the normal range, altering the biological function of the gene. These sequence are unstable and increase in size between family members in successive generations, giving rise to greater severity of disease. 4. Several workers have reported an association of trinucleotide repeat length with adult- and child-onset schizophrenia. One such expanded allele has been found at the CTG18.1 locus on the 18th chromosome. Other genes known to have similar mutation are SEF2-1, which codes for a helix-loop-helix protein, hSKCa3 gene, which codes for a calcium-activated potassium channel and the transthyretin gene. In schizophrenic patients, significant difference in allele frequency distribution of these genes has been reported. 5. Population based genetic research would not only help identify different subgroups of this of schizophrenia.

Pharmacological characterisation of the human small conductance calcium-activated potassium channel hSK3 reveals sensitivity to tricyclic antidepressants and antipsychotic phenothiazines

A stable CHO-K1 cell line was developed which expresses the human small conductance calcium-activated potassium channel hSK3. Immunofluorescence microscopy using an anti-SK3 antibody and radioligand binding using [(125)I]-apamin demonstrated the presence of hSK3 channel in the recombinant cell line. This cell line was utilised in a fluorescence assay using the membrane potential-sensitive dye DiBAC(4)(3) to functionally analyse and pharmacologically characterise this potassium channel. The analysis of known blockers of calcium-activated potassium channels revealed the highest potency for apamin (IC(50)=13.2 nM). This result was confirmed by direct recordings of SK3 currents using the whole-cell patch-clamp technique. Tricyclic antidepressants such as desipramine, imipramine and nortriptyline as well as phenothiazines such as fluphenazine, promethazine, chlorpromazine and trifluoperazine blocked the hSK3 channel with micromolar potencies. These compounds also displaced [(125)I]-apamin binding to the hSK3 channel thus suggesting direct and competitive channel blocking activity. Since these compounds share a common three-ring molecular core structure, this feature seems to be important for channel blocking activity. The serine/threonine protein phosphatase inhibitors okadaic acid and calyculin A were able to abolish channel activation with nanomolar potencies, but did not displace [(125)I]-apamin binding. Thus, phosphorylation of hSK3 or an accessory channel subunit seems to be involved in its modulation.

Association study of CAG repeats in the KCNN3 gene in Japanese patients with schizophrenia, schizoaffective disorder and bipolar disorder

To investigate a possible involvement of expanded triplet repeats of genome in the genomes of patients with endogenous psychoses, we examined a CAG repeat polymorphism in the coding region of the KCNN3 gene in schizophrenia, schizoaffective disorder, bipolar disorder and controls of the Japanese population. There were no significant differences in the CAG repeat number of longer or shorter alleles among the four diagnostic groups or among the schizophrenia hebephrenic and paranoid subtypes.

Anticipation, imprinting, trinucleotide repeat expansions and psychoses

1. Since 1991, approximately 20 trinucleotide repeat expansion type neurodegenerative disorders have been reported. They are clinically characterized by anticipation, i.e., worsening severity or earlier age at onset with each succeeding generation for an inherited disease, and imprinting, i.e., a process whereby specific genes are differentially marked during parental gametogenesis, resulting in the differential expression of these genes in the embryo and adult. 2. The phenomenon of anticipation in psychoses has been pointed out since the 19th century; however, it was ignored because no one knew the genetic mechanism underlying this type of inheritance pattern at the time, and because of several possible biases. 3. The discovery of trinucleotide repeat expansion diseases has reawakened interest in the phenomenon of anticipation in psychiatric diseases. Anticipation has been confirmed in schizophrenia, mood disorders, and anxiety disorders in much more sophisticated manners, although still not perfectly. 4. Molecular approaches as well as clinical ones have been taken to reveal the involvement of trinucleotide repeat expansion mechanism in psychoses by means of direct analyses of candidate genes, RED and DIRECT. Most efforts have been made for CAG type trinucleotide repeats. So far, direct analyses have failed to reveal pathogenic gene(s). There were several positive RED data at first, however, nowadays there seems to be a tendency of much more negative results. The DIRECT results did not support trinucleotide repeat expansions mechanism in psychoses either. One plausable explanation for the 'false positive' result is the presence of CAG trinucleotide repeats which are highly polymorphic but not associated with an obvious abnormal phenotype. Screening for trinucleotide repeats other than ones of the CAG type remained to be performed.

Association analysis of CAG repeats at the KCNN3 locus in Indian patients with bipolar disorder and schizophrenia

Bipolar affective disorder and schizophrenia are severe behavioral disorders with a lifetime risk of approximately 1% in the population worldwide. There is evidence that these diseases may manifest the phenomenon of anticipation similar to that seen in diseases caused by trinucleotide repeat expansions. A recent report has implicated a potassium channel-coding gene, KCNN3, which contains a polymorphic CAG repeat in its coding region, in schizophrenia and bipolar disorder. We have tried to confirm these findings in Indian patients suffering from bipolar disorder and schizophrenia. No statistically significant evidence for the presence of an excess of longer alleles in the patient population, as compared to ethnically matched controls, was found. However, an analysis of the difference of allele sizes revealed a significantly greater number of patients with schizophrenia having differences of allele sizes > or = 5 when compared to normal controls. This finding may be of functional significance as the KCNN3 protein is thought to act as a tetramer, and a large difference in allele sizes would result in an asymmetric molecule with a different number of glutamine residues in each monomer. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:744-748, 2000.

No evidence of association from transmission disequilibrium analysis of the hKCa3 gene in bipolar disorder

OBJECTIVE

A recent case control study has suggested that modest enlargements of a highly polymorphic CAG repeat in exon 1 of the gene encoding potassium channel hKCa3 may be associated with bipolar disorder (BPD). We have examined this hypothesis by genotyping this locus in a family-based association study.

METHOD

One hundred and twenty-eight parent offspring trios of British Caucasian origin were examined where the proband was diagnosed with the American Psychiatric Association's Diagnostic and Statistical Manual (DSM)-IV BPD I (n = 123) or II (n = 5). An improved assay was used, with redesigned polymerase chain reaction (PCR) primers, permitting quicker and higher resolution genotyping. The resultant genotypes were analysed using the extended transmission/ disequilibrium test (ETDT).

RESULTS

The experimental data did not provide evidence for the preferential transmission of large alleles to bipolar cases (chi2 = 11.12, df = 10, p = 0.349).

CONCLUSIONS

Our data provide no support for the hypothesis that variation at the hKCa3 gene contributes to susceptibility to BPD.

Genetic analyses of schizophrenia

Although evidence exists to support a heritable component to schizophrenia, few details are understood about the genetics of the disorder. Presently, molecular genetic techniques provide the most promise in uncovering the genetic mechanisms of disease. Candidate gene analyses and linkage studies have opened some prospective avenues for exploration. Clearer findings from these studies many be hidden by the syndromic nature of schizophrenia. The study of more genetically homogenous populations and symptom-based phenotypic subtypes may help to make this genetic data more revealing. This review highlights some of the latest progress and findings in the molecular genetic analyses of schizophrenia, including both candidate gene analyses and genome scan studies.