Evidence for genetic heterogeneity between clinical subtypes of bipolar disorder.

We performed a genome-wide association study of 6447 bipolar disorder (BD) cases and 12 639 controls from the International Cohort Collection for Bipolar Disorder (ICCBD). Meta-analysis was performed with prior results from the Psychiatric Genomics Consortium Bipolar Disorder Working Group for a combined sample of 13 902 cases and 19 279 controls. We identified eight genome-wide significant, associated regions, including a novel associated region on chromosome 10 (rs10884920; P=3.28 × 10-8) that includes the brain-enriched cytoskeleton protein adducin 3 (ADD3), a non-coding RNA, and a neuropeptide-specific aminopeptidase P (XPNPEP1). Our large sample size allowed us to test the heritability and genetic correlation of BD subtypes and investigate their genetic overlap with schizophrenia and major depressive disorder. We found a significant difference in heritability of the two most common forms of BD (BD I SNP-h2=0.35; BD II SNP-h2=0.25; P=0.02). The genetic correlation between BD I and BD II was 0.78, whereas the genetic correlation was 0.97 when BD cohorts containing both types were compared. In addition, we demonstrated a significantly greater load of polygenic risk alleles for schizophrenia and BD in patients with BD I compared with patients with BD II, and a greater load of schizophrenia risk alleles in patients with the bipolar type of schizoaffective disorder compared with patients with either BD I or BD II. These results point to a partial difference in the genetic architecture of BD subtypes as currently defined.

GWA study data mining and independent replication identify cardiomyopathy-associated 5 (CMYA5) as a risk gene for schizophrenia.

We conducted data-mining analyses using the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) and molecular genetics of schizophrenia genome-wide association study supported by the genetic association information network (MGS-GAIN) schizophrenia data sets and performed bioinformatic prioritization for all the markers with P-values ≤0.05 in both data sets. In this process, we found that in the CMYA5 gene, there were two non-synonymous markers, rs3828611 and rs10043986, showing nominal significance in both the CATIE and MGS-GAIN samples. In a combined analysis of both the CATIE and MGS-GAIN samples, rs4704591 was identified as the most significant marker in the gene. Linkage disequilibrium analyses indicated that these markers were in low LD (3 828 611-rs10043986, r(2)=0.008; rs10043986-rs4704591, r(2)=0.204). In addition, CMYA5 was reported to be physically interacting with the DTNBP1 gene, a promising candidate for schizophrenia, suggesting that CMYA5 may be involved in the same biological pathway and process. On the basis of this information, we performed replication studies for these three single-nucleotide polymorphisms. The rs3828611 was found to have conflicting results in our Irish samples and was dropped out without further investigation. The other two markers were verified in 23 other independent data sets. In a meta-analysis of all 23 replication samples (family samples, 912 families with 4160 subjects; case-control samples, 11 380 cases and 15 021 controls), we found that both markers are significantly associated with schizophrenia (rs10043986, odds ratio (OR)=1.11, 95% confidence interval (CI)=1.04-1.18, P=8.2 × 10(-4) and rs4704591, OR=1.07, 95% CI=1.03-1.11, P=3.0 × 10(-4)). The results were also significant for the 22 Caucasian replication samples (rs10043986, OR=1.11, 95% CI=1.03-1.17, P=0.0026 and rs4704591, OR=1.07, 95% CI=1.02-1.11, P=0.0015). Furthermore, haplotype conditioned analyses indicated that the association signals observed at these two markers are independent. On the basis of these results, we concluded that CMYA5 is associated with schizophrenia and further investigation of the gene is warranted.

Integrating genetic, functional genomic, and bioinformatics data in a systems biology approach to complex diseases: application to schizophrenia.

The search for DNA alterations that cause human disease has been an area of active research for more than 50 years, since the time that the genetic code was first solved. In the absence of data implicating chromosomal aberrations, researchers historically have performed whole genome linkage analysis or candidate gene association analysis to develop hypotheses about the genes that most likely cause a specific phenotype or disease. Whereas whole genome linkage analysis examines all chromosomal locations without a priori predictions regarding what genes underlie susceptibility, candidate gene association studies require a researcher to know in advance the genes that he or she wishes to test (based on their knowledge of a disease). To date, very few whole genome linkage studies and candidate gene studies have produced results that lead to generalizable findings about common diseases. One factor contributing to this lack of results has certainly been the previously limited resolution of the techniques. Recent technological advances, however, have made it possible to perform highly informative whole genome linkage and association analyses, as well as whole genome transcription (transcriptome) analysis. In addition, for the first time we can detect structural DNA aberrations throughout the genome on a fine scale. Each of these four approaches has its own strengths and weaknesses, but taken together, the results from an integrated analysis can implicate highly promising novel candidate genes. Here, we provide an overview of the integrated methodology that we have used to combine high-throughput genetic and functional genomic data with bioinformatics data that have produced new insights into the potential biological basis for schizophrenia. We believe that the potential of this combined approach is greater than that of a single mode of discovery, particularly for complex genetic diseases.

Genetic investigation of chromosome 5q GABAA receptor subunit genes in schizophrenia.

We previously performed a genome-wide linkage scan in Portuguese schizophrenia families that identified a risk locus on chromosome 5q31-q35. This finding was supported by meta-analysis of 20 other schizophrenia genome-wide scans that identified 5q23.2-q34 as the second most compelling susceptibility locus in the genome. In the present report, we took a two-stage candidate gene association approach to investigate a group of gamma-aminobutyric acid (GABA) A receptor subunit genes (GABRA1, GABRA6, GABRB2, GABRG2, and GABRP) within our linkage peak. These genes are plausible candidates based on prior evidence for GABA system involvement in schizophrenia. In the first stage, associations were detected in a Portuguese patient sample with single nucleotide polymorphisms (SNPs) and haplotypes in GABRA1 (P=0.00062-0.048), GABRP (P=0.0024-0.042), and GABRA6 (P=0.0065-0.0088). The GABRA1 and GABRP findings were replicated in the second stage in an independent German family-based sample (P=0.0015-0.043). Supportive evidence for association was also obtained for a previously reported GABRB2 risk haplotype. Exploratory analyses of the effects of associated GABRA1 haplotypes on transcript levels found altered expression of GABRA6 and coexpressed genes of GABRA1 and GABRB2. Comparison of transcript levels in schizophrenia patients and unaffected siblings found lower patient expression of GABRA6 and coexpressed genes of GABRA1. Interestingly, the GABRA1 coexpressed genes include synaptic and vesicle-associated genes previously found altered in schizophrenia prefrontal cortex. Taken together, these results support the involvement of the chromosome 5q GABAA receptor gene cluster in schizophrenia, and suggest that schizophrenia-associated haplotypes may alter expression of GABA-related genes.

Support for involvement of neuregulin 1 in schizophrenia pathophysiology.

Schizophrenia is a common, multigenic psychiatric disorder. Linkage studies, including a recent meta-analysis of genome scans, have repeatedly implicated chromosome 8p12-p23.1 in schizophrenia susceptibility. More recently, significant association with a candidate gene on 8p12, neuregulin 1 (NRG1), has been reported in several European and Chinese samples. We investigated NRG1 for association in schizophrenia patients of Portuguese descent to determine whether this gene is a risk factor in this population. We tested NRG1 markers and haplotypes for association in 111 parent-proband trios, 321 unrelated cases, and 242 control individuals. Associations were found with a haplotype that overlaps the risk haplotype originally reported in the Icelandic population ("Hap(ICE)"), and two haplotypes located in the 3' end of NRG1 (all P<0.05). However, association was not detected with Hap(ICE) itself. Comparison of NRG1 transcript expression in peripheral leukocytes from schizophrenia patients and unaffected siblings identified 3.8-fold higher levels of the SMDF variant in patients (P=0.039). Significant positive correlations (P<0.001) were found between SMDF and HRG-beta 2 expression and between HRG-gamma and ndf43 expression, suggesting common transcriptional regulation of NRG1 variants. In summary, our results suggest that haplotypes across NRG1 and multiple NRG1 variants are involved in schizophrenia.

Genomewide linkage analysis of bipolar disorder by use of a high-density single-nucleotide-polymorphism (SNP) genotyping assay: a comparison with microsatellite marker assays and finding of significant linkage to chromosome 6q22.

We performed a linkage analysis on 25 extended multiplex Portuguese families segregating for bipolar disorder, by use of a high-density single-nucleotide-polymorphism (SNP) genotyping assay, the GeneChip Human Mapping 10K Array (HMA10K). Of these families, 12 were used for a direct comparison of the HMA10K with the traditional 10-cM microsatellite marker set and the more dense 4-cM marker set. This comparative analysis indicated the presence of significant linkage peaks in the SNP assay in chromosomal regions characterized by poor coverage and low information content on the microsatellite assays. The HMA10K provided consistently high information and enhanced coverage throughout these regions. Across the entire genome, the HMA10K had an average information content of 0.842 with 0.21-Mb intermarker spacing. In the 12-family set, the HMA10K-based analysis detected two chromosomal regions with genomewide significant linkage on chromosomes 6q22 and 11p11; both regions had failed to meet this strict threshold with the microsatellite assays. The full 25-family collection further strengthened the findings on chromosome 6q22, achieving genomewide significance with a maximum nonparametric linkage (NPL) score of 4.20 and a maximum LOD score of 3.56 at position 125.8 Mb. In addition to this highly significant finding, several other regions of suggestive linkage have also been identified in the 25-family data set, including two regions on chromosome 2 (57 Mb, NPL = 2.98; 145 Mb, NPL = 3.09), as well as regions on chromosomes 4 (91 Mb, NPL = 2.97), 16 (20 Mb, NPL = 2.89), and 20 (60 Mb, NPL = 2.99). We conclude that at least some of the linkage peaks we have identified may have been largely undetected in previous whole-genome scans for bipolar disorder because of insufficient coverage or information content, particularly on chromosomes 6q22 and 11p11.

Genome-wide scan in Portuguese Island families identifies 5q31-5q35 as a susceptibility locus for schizophrenia and psychosis.

Schizophrenia is a common psychiatric disorder with a complex genetic etiology. To understand the genetic basis of this syndrome in Portuguese Island populations, we performed a genome-wide scan of 29 families with schizophrenia, which identified a single region on 5q31-5q35 with strong linkage (NPL=3.09, P=0.0012 at D5S820). Empirical simulations set a genome-wide threshold of NPL=3.10 for significant linkage. Additional support for this locus in schizophrenia comes from higher-density mapping and mapping of 11 additional families. The combined set of 40 families had a peak NPL=3.28 (P=0.00066) at markers D5S2112-D5S820. These data and previous linkage findings from other investigators provide strong and consistent evidence for this genomic region as a susceptibility locus for schizophrenia. Exploratory analyses of a novel phenotype, psychosis, in families with schizophrenia and bipolar disorder detected evidence for linkage to the same markers as found in schizophrenia (peak NPL=3.03, P=0.0012 at D5S820), suggesting that this locus may be responsible for the psychotic symptoms observed in both diseases. Molecular Psychiatry (2004) 9, 213-218. doi:10.1038/sj.mp.4001418 Published online 30 December 2003

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.

Association and linkage disequilibrium between a functional polymorphism of the dopamine-2 receptor gene and schizophrenia in a genetically homogeneous Portuguese population.

A functional polymorphism in the promoter region of the DRD2 gene has been found to be associated with schizophrenia in Japanese(1,2) and Swedish populations.(3) We attempted to replicate these findings in a genetically homogeneous Portuguese population using a family-based study design. Analysis of 78 trios revealed evidence for association between the -141 C Ins allele and schizophrenia using the haplotype relative risk (HRR) method (chi(2) = 9.30, P = 0.0023). Further examination of this sample using an alternative family-based association analysis method, the transmission disequilibrium test (TDT), of 33 informative matings from the Portuguese trios provided evidence for an allelic association and linkage disequilibrium between the insertion allele and schizophrenia (chi(2) = 8.76, P = 0.0031). These consistent results using two alternative family-based association analysis methods replicate the findings of previous reports, and thus further implicate a potential role for the dopamine-2 receptor in the genetic etiology of schizophrenia.

The genetics of obsessive-compulsive disorder.

A significant amount of evidence has been gathered to suggest that obsessive-compulsive disorder (OCD) is a heritable disease. Despite this information, few details are understood about the genetics of the disorder. Molecular genetic techniques, especially candidate-gene association studies, have been used to try to appreciate the genetic components of this complex disorder. In addition to the complex inheritance pattern, the heterogeneous nature of the disorder complicates the analyses. This review outlines the evidence that has been gathered to date, implicating OCD as a genetic disorder. In addition, the most interesting and recent findings in the molecular genetic analyses are highlighted.

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.

Association between homozygosity at the COMT gene locus and obsessive compulsive disorder.

A functional polymorphism in the coding region of the catechol O-methyltransferase (COMT) gene has been reported in previous studies to be associated with obsessive compulsive disorder (OCD), particularly in males [Karayiorgou et al., 1997, 1999]. Using a family-based population analysis, we attempted to replicate these findings in a group of 72 OCD patient/parent trios collected from Buffalo, New York, and Toronto, Canada. Analysis of allele and genotype frequencies using the haplotype relative risk (HRR) and transmission disequilibrium test (TDT) did not identify an association between a particular allele and OCD as had been previously reported. Furthermore, no evidence was found to support the findings of a gender-based association for COMT when the patients and the parents of the same gender were compared. However, our genotype results (n = 72) demonstrate a tendency for association between homozygosity at the COMT locus and OCD (homozygosity analysis: chi(2) = 5.66, P = 0.017; genotypic analysis: chi(2) = 5.78, P = 0.056). Although these findings do not replicate the previous reports, they do provide limited support to demonstrate a trend for homozygosity at the COMT locus in the OCD patients and, in turn, further implicate a potential role for COMT in the genetic etiology of OCD. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:721-724, 2000.

Detection of expansion regions in Portuguese bipolar families.

We have studied 24 families with multiple affected members with bipolar disorder to test the hypothesis that in those families clinically showing genetic anticipation [Macedo et al., 1999] we would find large repeat expansions. The families meeting inclusion criteria had a minimum of two affected members over two generations and showed marked anticipation both in terms of age of onset and disease severity. We used the repeat expansion detection (RED) method to test patients (n = 24) and controls from these families and unrelated controls (n = 53). We also genotyped patients and family members from two families with large expansions at the known expansion loci on chromosomes 13, 17, and 18. The RED method revealed a higher number of large expansions in patients compared with controls (t-test; P < 0.0055: Mann-Whitney U; P = 0.02). The patients with the largest expansions were typed at the specific loci on chromosomes 13, 17, and 18 and the chromosome 18 expansion locus segregated with disease in one family, and a second family showed segregation with the expansion located at the SCA8 locus on chromosome 13. Genetic anticipation had been analyzed in this cohort of families, with correction for potential ascertainment bias, possible proband effects, cohort effects, regression to the mean, gender effects, and maternal vs. paternal transmission. None of these potential confounds appeared to account for the observed anticipation. We also identified that the presence of large expansions in affected family members derives primarily from two families from the genetically isolated Azores population. One family shows segregation with the chromosome 18 locus, whereas the other family segregates with expansions at the SCA8 locus. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:854-857, 2000.

Long repeat tracts at SCA8 in major psychosis.

Expansion at a recently identified unstable trinucleotide repeat on chromosome 13q21 has been reported as the molecular cause for spinocerebellar ataxia type 8 (SCA8). The trinucleotide repeat, which consists of a [CTA]n repeat and adjacent [CTG]n repeat, was reported to have a pathogenic range of 107-127 CTG repeats (or 110-130 combined CTA and CTG repeats) in a large ataxia kindred. This repeat region was also cloned by our group from a bipolar affective disorder (BPAD) patient, who has approximately 600 combined repeats, and large alleles (>100 repeats) were reported to be present in 0.7% of controls and 1.5% of major psychosis patients (n = 710 and n = 1,120, respectively). We have followed up these findings by screening three new samples of BPAD and schizophrenia (SCZ) patients and controls, including 272 individuals from 14 BPAD families from Sweden, 130 individuals from 32 SCZ and BPAD families/trios from the Azores Islands, and 206 SCZ individuals from the United Kingdom and Ireland, and 219 matched controls. We found large repeat alleles above the SCA8 pathogenic range in individuals from 3 of 32 Azorean pedigrees and in 1 of 206 SCZ individuals from the United Kingdom, and repeat alleles within the SCA8 pathogenic range in 1 of 14 Swedish families. Although the rarity of major psychosis patients carrying the SCA8 expansion mutation would require a much larger sample size to reach statistical significance, these results support the previously reported observation of increased occurrence of large repeats at SCA8 in major psychosis. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:873-876, 2000.

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.

An unstable trinucleotide-repeat region on chromosome 13 implicated in spinocerebellar ataxia: a common expansion locus.

Larger CAG/CTG trinucleotide-repeat tracts in individuals affected with schizophrenia (SCZ) and bipolar affective disorder (BPAD) in comparison with control individuals have previously been reported, implying a possible etiological role for trinucleotide repeats in these diseases. Two unstable CAG/CTG repeats, SEF2-1B and ERDA1, have recently been cloned, and studies indicate that the majority of individuals with large repeats as detected by repeat-expansion detection (RED) have large repeat alleles at these loci. These repeats do not show association of large alleles with either BPAD or SCZ. Using RED, we have identified a BPAD individual with a very large CAG/CTG repeat that is not due to expansion at SEF2-1B or ERDA1. From this individual's DNA, we have cloned a highly polymorphic trinucleotide repeat consisting of (CTA)n (CTG)n, which is very long ( approximately 1,800 bp) in this patient. The repeat region localizes to chromosome 13q21, within 1.2 cM of fragile site FRA13C. Repeat alleles in our sample were unstable in 13 (5.6%) of 231 meioses. Large alleles (>100 repeats) were observed in 14 (1. 25%) of 1,120 patients with psychosis, borderline personality disorder, or juvenile-onset depression and in 5 (.7%) of 710 healthy controls. Very large alleles were also detected for Centre d'Etude Polymorphisme Humaine (CEPH) reference family 1334. This triplet expansion has recently been reported to be the cause of spinocerebellar ataxia type 8 (SCA8); however, none of our large alleles above the disease threshold occurred in individuals either affected by SCA or with known family history of SCA. The high frequency of large alleles at this locus is inconsistent with the much rarer occurrence of SCA8. Thus, it seems unlikely that expansion alone causes SCA8; other genetic mechanisms may be necessary to explain SCA8 etiology.

European Multicentre Association Study of Schizophrenia: a study of the DRD2 Ser311Cys and DRD3 Ser9Gly polymorphisms.

As part of the European Multicentre Association Study of Schizophrenia (EMASS), we studied polymorphisms in the dopamine DRD2 and DRD3 receptor genes. The EMASS collaboration was established to create a large, statistically powerful sample of schizophrenic patients and controls from different European centres. Previous studies have suggested associations between schizophrenia and the Ser311Cys polymorphism in exon 7 of the dopamine DRD2 receptor gene [Arinami et al., (1994): Lancet 343:703-704] and a polymorphism Ser9gly in exon 1 of the dopamine DRD3 receptor gene [Crocq et al. (1992): J Med Genet 29:858-860]. We tested for these associations in samples of 373 and 413, and 311 and 306 patients and controls, respectively. We found no evidence for allelic association between schizophrenia and the Cys311 variant of the DRD2 receptor gene and no homozygotes for this variant were observed by any group. However, an excess of homozygotes for both alleles of the DRD3 polymorphism was observed in schizophrenic patients (chi2 = 8.54, P = 0.003, odds ratio = 1.64, 95% CI = 1.18-2.29). We also observed a significant excess of the 1-1 (Ser9Ser) genotype (chi2 = 8.13, P = 0.004, odds ratio = 1.7, 95% CI = 1.18-2.4). No evidence of heterogeneity between samples was detected and there was no evidence of an allelic association. These findings suggest that the rare Cys311 variant in exon 7 of the DRD2 receptor gene does not play a role in the pathogenesis of schizophrenia in European populations. Currently, our results do support the previous findings of an association between increased homozygosity of the Ser/Gly variant of the Dopamine D3 receptor gene and schizophrenia.

Selection of homogeneous populations for genetic study: the Portugal genetics of psychosis project.

Molecular genetic studies of psychiatric disorders must face the possibility that despite the significant contribution of genetic factors to the expression of syndromes like schizophrenia, these syndromes may be a heterogeneous collection of genetic and non-genetic illnesses. These illnesses may be etiologically distinct from each other and still share many clinical features in common. Linkage studies of families with multiple affected members tend to favor the selection of genetic forms of a syndrome but can still represent a heterogeneous set of different genetic illnesses. To limit the potential genetic heterogeneity of a study sample, we selected a population that was geographically isolated and was historically relatively genetically homogeneous. We then assessed the relative level of homogeneity utilizing a surname analysis of the population of the Azores, mainland Portugal, rural USA, and urban USA. The average number of families with the same last name corrected for population size in the Azores is 30.88, in Coimbra it is 21.42, compared to 1.13 in a rural American population and 0.38 in an urban American population. The results of this analysis indicate that the Azores have the highest degree of homogeneity, and mainland Portugal has a high degree of homogeneity.

Expanded CAG/CTG repeats in schizophrenia. A study of clinical correlates.

BACKGROUND: Schizophrenia is associated with expanded CAG/CTG trinucleotide repeats. We wished to determine whether the presence of such expansions correlated with specific subsyndromes or other clinical features of schizophrenia. METHOD: Seventy patients from England and Wales and 44 patients from Portugal with a DSM-III-R diagnosis of schizophrenia were rated on the OPCRIT checklist. Patient's maximum CAG/CTG repeat length was measured using repeat expansion detection (RED). Significant differences were sought for repeat lengths in subjects categorised according to dimensional and categorical schizophrenia subsyndromes, affective episodes, individual symptoms, and a range of demographic variables. RESULTS: Maximum CAG/CTG repeat length did not differ significantly for any of the clinical or demographic variables studied. CONCLUSION: There are no subsyndromes or other clinical features of schizophrenia associated with CAG/CTG repeat expansion. Therefore, the identification of the gene(s) that contain expanded CAG/CTG repeats and which are associated with schizophrenia is unlikely to be facilitated at present by using any subsyndromes of schizophrenia as phenotypes.

Comorbidity of obsessive-compulsive and psychotic symptoms: a review.

Co-occurrence of psychotic and obsessive-compulsive symptoms was first reported nearly 70 years ago. This paper reviews published reports from two perspectives: psychotic disorders with obsessive-compulsive symptoms and obsessive-compulsive disorder (OCD) with psychotic symptoms. Older investigations reported a low rate of comorbidity between these two disorders, but more-recent studies, in which systematic diagnostic criteria have been used, have suggested that the rate of co-occurrence of symptoms is higher than was previously thought. The difficulty in diagnosing patients with obsessive-compulsive and psychotic symptoms is reviewed, and the importance of this distinction for treatment and prognosis is discussed. Although the comorbid diagnosis of schizophrenia and OCD, or of OCD and psychotic features, seems to portend a worse prognosis than for either illness alone, the available data suggest that some patients with schizophrenia and OC symptoms may improve with traditional antiobsessional treatment.