Autosome search for schizophrenia susceptibility genes in multiply affected families

We have analysed 298 polymorphic markers in 13 families multiply affected with schizophrenia and related disorders using a combination of radiolabelled and fluorescent-based methodologies. The markers were distributed throughout the autosomes at an average spacing of 12.8 cM. The data were analysed with two-point linkage analysis (MLINK) and heterogeneity testing (HOMOG). Several genetic models were used ranging from near dominant to fully recessive. Multi-point analysis was performed for 27 regions demonstrating either contiguously positive lod scores in two or more consecutive markers, and in regions with two-point lod score(s) of 1.0 or above in a single marker. A proportion of the multi-point regions have been implicated in previous studies, thereby decreasing risk of false-positive results. However neither our two-point, nor multi-point scores reached the threshold value for significance of 3. 6. Nevertheless three regions were suggestive of linkage.

A study of chromosome 4p markers and dopamine D5 receptor gene in schizophrenia and bipolar disorder

There are several lines of evidence which suggest that chromosome 4p may contain a major susceptibility locus for the functional psychoses. We previously reported a family (family 50) with cases of schizophrenia and schizoaffective disorder which gave maximum lod scores of 1.96 and 1.84 respectively with the markers D4S403 and a microsatellite near to DRD5 (DRD5-M). More recently Blackwood and co-workers described a family segregating bipolar and unipolar affective disorders which gives a maximum lod score of 4.1 with the marker D4S394, which lies 10 cM from D4S403. They obtained a combined maximum lod of 3.3 in their total sample of 12 bipolar families and found significant evidence of heterogeneity (chi 2 = 18.8, df = 2, P = 0.00008). Here we report the results of a linkage study of chromosome 4p markers in a sample of 24 multiply affected families with schizophrenia and related disorders. We obtained an overall maximum lod of 1.12 with D4S403 under both dominant and recessive modes of transmission, with no statistical support for heterogeneity within our sample. Examination of family by family data shows that only family 50 appears to show linkage at this locus. However, a discrepancy exists since our study examined families fulfilling criteria for a linkage study of schizophrenia while Blackwood et al examined families included in a genetic linkage study of bipolar disorder. This may be explained by the clinical features displayed by members of family 50, which show that all the affected members have some affective symptoms. It is therefore possible that a broad phenotype including unipolar depression, bipolar disorder, schizoaffective disorder and schizophrenia when accompanied by significant affective symptoms can result from mutations within a gene in this region. The dopamine D5 receptor gene lies within the region identified by the linkage studies and is therefore a major candidate for the putative disease gene. In family 50 we have looked for mutations of DRD5 by sequence analysis of the coding region and single stranded conformational polymorphism (SSCP) analysis of the promoter. SSCP analysis of the coding and promoter regions have also been carried out in unrelated cases of DSM-IIIR schizophrenia. Finally association studies of the (TC)n repeat in the promoter and schizophrenia, and DRD5-M and bipolar disorder were performed. These studies provided no further evidence supporting the possibility that mutations in DRD5 give rise to the linkage findings or are acting as susceptibility loci in schizophrenia or bipolar disorder.

Polymerase chain reaction and restriction fragment length polymorphism mediated detection and speciation of Candida spp causing intraocular infection

PURPOSE

To determine the usefulness of polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analysis in the identification and speciation of Candida spp that causes ocular infection.

METHODS

Oligonucleotide primers based on the cytochrome P450 L1 A1 demethylase gene were used to successfully amplify by PCR a single 1.0-kb and a single 500-bp DNA fragment from C. albicans, C. tropicalis, C. krusei, C. glabrata, C. parapsilosis, and C. pelliculosa genomic DNA. RFLPs within the PCR product were identified after restriction enzyme digestion.

RESULTS

The sensitivity of the amplification reaction after two rounds of PCR was 10 fg genomic C. albicans DNA or one copy of the gene. No amplification product was obtained when DNA from C. guilliermondii, Aspergillus fumigatus, Fusarium solani, human leukocytes, or 10 species of bacteria was used as a template. Experiments with spiked normal vitreous demonstrated equal sensitivity as long as the volume of vitreous did not exceed 20% of the total PCR volume. RFLP analysis of the PCR product generated from each species obtained from the first- and second-round amplification products enabled species identification after digestion with specific endonucleases. Application of the technique to four clinical samples was successful.

CONCLUSIONS

It is expected that the simplicity of the DNA extraction technique allied with the broad specificity of the outer primers for all ophthalmically relevant Candida spp and the sensitivity of the second-round PCR will aid in the detection of fungal DNA in small intraocular samples. PCR-RFLP analysis has great potential in the rapid detection and identification of Candida spp and in the provision of a useful laboratory tool for the future.

A meta-analysis and transmission disequilibrium study of association between the dopamine D3 receptor gene and schizophrenia

We performed a meta-analysis of over 30 case-control studies of association between schizophrenia and a bi-allelic, Bali polymorphism in exon 1 of the dopamine D3 receptor gene. We observed a significant excess of both forms of homozygote in patients (P = 0.0009, odds ratio (OR) = 1.21, 95% Confidence Interval (CI) = 1.07-1.35) in the combined sample of 5351 individuals. No significant heterogeneity was detected between samples and the effects did not appear to be the product of publishing bias. In addition we undertook an independent, family-based association study of this polymorphism in 57 parent/proband trios, taken from unrelated European multiplex families segregating schizophrenia. A transmission disequilibrium test (TDT) showed a significant excess of homozygotes in schizophrenic patients (P = 0.004, odds ratio (OR) = 2.7, 95% CI = 1.35-5.86). Although no significant allelic association was observed, a significant association was detected with the 1-1 genotype alone (P = 0.02, OR = 2.32, 95% CI = 1.13-4.99). In addition when the results of the family-based association study were included in the meta-analysis, the homozygosity effect increased in significance (P = 0.0002, OR = 1.23, 95% CI = 1.09-1.38). The results of the meta-analysis and family-based association study provide independent support for a relationship between schizophrenia and homozygosity at the Bali polymorphism of the D3 receptor gene, or between a locus in linkage disequilibrium with it.

No evidence for linkage between schizophrenia and eight microsatellite markers on chromosome 19

We report the results of a linkage study of eight markers on chromosome 19 in a sample of 24 families multiply affected with schizophrenia and related psychoses. This study forms part of a systematic search of the entire genome using microsatellite markers spaced at 10-20 cM intervals. These data provide no evidence for the presence of a gene of major effect on chromosome 19 under the assumption of genetic homogeneity or heterogeneity. We have attempted to describe the extent to which this region has been excluded and demonstrate that while it is possible to exclude near-dominant and recessive models under the assumption that all families are linked to the same locus, power for exclusion falls away rapidly when incomplete penetrance and heterogeneity are invoked.

Linkage, association and mutational analysis of the dopamine D3 receptor gene in schizophrenia

This study follows the observation of an association between homozygosity of an Mscl polymorphism in exon 1 and schizophrenia, which gives rise to a glycine to serine substitution and may alter the functional properties of the receptor. Alternatively the polymorphism may not itself be of functional significance but may be in linkage disequilibrium with another genetic variant in the coding or regulatory regions. To examine the second possibility we have screened all six exons of DRD3 by single-stranded conformational polymorphism analysis (SSCP) in 36 cases and 36 controls. Our findings suggest that the gene is highly conserved since we found no other mutations which alter protein structure. However we did detect a 5-bp deletion in the 3' intronic sequence flanking exon 5 which occurred in 7-8% of subjects within both case and control samples. A single bp substitution (g to a) in exon 3, which does not alter an amino acid was found in one affected individual. In addition we carried out a linkage study of 24 families multiply affected with schizophrenia and a non-parametric linkage study of 90 affected sibling pairs. These studies give no support for either major or moderate gene effects on schizophrenia susceptibility. Finally we have extended our association sample and observe a non-significant excess of homozygotes for the Mscl polymorphism in the sample overall (chi 2 = 2.09, 1 d.f., P = 0.15). The excess of homozygotes is specific to males (chi 2 = 4.617, 1 d.f., P = 0.032) and not females (chi 2 = 0.243, 1 d.f., NS). When these data are added to our previous published data a highly significant excess of homozygotes is observed in males (chi 2 = 13.766, 1 d.f., P = 0.00021) but not females (chi 2 = 0.606, 1 d.f., NS). In conclusion the accumulated data suggest strongly that genetic variation at the DRD3 locus increases susceptibility of schizophrenia, at least in males. At present the Mscl polymorphism in exon 1 of the gene remains a candidate for bringing about functional change in the receptor but this has not been formally tested. Other coding region polymorphisms have not been detected but it remains possible that variation within the promoter may alter receptor function.

Clinical features of early onset, familial Alzheimer's disease linked to chromosome 14

Early onset familial Alzheimer's disease (AD) has an autosomal dominant mode of inheritance. Two genes are responsible for the majority of cases of this subtype of AD. Mutations in the beta-amyloid precursor protein (beta APP) gene on chromosome 21 have been shown to completely cosegregate with the disease. We and others have previously described the clinical features of families with beta APP mutations at the codon 717 locus in an attempt to define the phenotype associated with a valine to isoleucine (Val-->Ile) or a valine to glycine (Val-->Gly) change. More recently, a second locus for very early onset disease has been localized to chromosome 14. The results of linkage studies in some families suggesting linkage to both chromosomes have been explained by the suggestion of a second (centromeric) locus on chromosome 21. Here we report the clinical features and genetic analysis of a British pedigree (F74) with early onset AD in which neither the beta APP locus nor any other chromosome 21 locus segregates with the disease, but in which good evidence is seen for linkage on the long arm of chromosome 14. In particular we report marker data suggesting that the chromosome 14 disease locus is close to D14S43 and D14S77. Given the likelihood that F74 represents a chromosome 14 linked family, we describe the clinical features and make a limited clinical comparison with the beta APP717 Val-->Ile and beta APP717 Val-->Gly encoded families that have been previously described.(ABSTRACT TRUNCATED AT 250 WORDS)

Repeat length variation in the dopamine D4 receptor gene shows no evidence of association with schizophrenia

The D4 receptor has been shown to exist in several allelic forms (Van Tol et al., Nature 358:149-152, 1992) reflecting variation in the number of 48 base-pair sequence repeats in the putative cytoplasmic loop. We report a comparison of repeat length variation between schizophrenic patients and controls. Our sample of 106 unrelated schizophrenic cases and 119 controls showed no significant differences in allele or genotype distribution between patients and controls. In particular, we were unable to support the previous observation of an excess of 4-repeat homozygotes in patients.

Relationship between homozygosity at the dopamine D3 receptor gene and schizophrenia

We have reported an association between schizophrenia and homozygosity of a Bal I polymorphism in the first exon of the dopamine D3 receptor gene (Crocq et al.: Journal of Medical Genetics 29:858-860, 1992). The present study consists of an attempt to replicate this finding in a further sample of 66 patients and 97 controls. Once again more patients than controls were homozygous, but the effect was not as strong as in our first study (chi 2 = 2.53, P = 0.05, one tailed). When pooled data from our two studies were analysed, excess homozygosity in patients remained highly significant (P = 0.002) with a particular excess of the 1:1 genotype (P = 0.01). This reflected a departure from Hardy-Weinberg equilibrium in the patients (P = 0.0005) but not the controls (P = 0.24). This led us to explore the possibility that there might be important differences between the patients in our two studies and that excess homozygosity might be a characteristic of particular subgroups of schizophrenics. Our findings suggest that the effect is consistently at its strongest in those patients who have a high familial loading and in those who have a good response to neuroleptic treatment, and that differences between our two samples might have contributed to the quantitatively different outcomes.

Bipolar affective puerperal psychosis associated with consanguinity

Most clinical and genetic evidence suggests that puerperal psychosis is closely related to bipolar affective disorder. During a linkage study of bipolar disorder we ascertained a British family in which puerperal psychosis was associated with consanguinity in three sisters. All three subjects had lifetime RDC diagnoses of bipolar I or manic disorder. An inbred brother also had bipolar I disorder. The only female member of the sibship to escape puerperal psychosis was outbred. These findings are consistent with several genetic models for bipolar disorder in this family. The most interesting possibility is a single major susceptibility locus of recessive effect. Under this assumption, the family could be used for homozygosity mapping to help localise the putative recessive locus. If other inbred families can be found in which the same putative recessive locus is operating, the power to localise the gene by homozygosity mapping would be greatly increased.

Failure to find linkage between schizophrenia and genetic markers on chromosome 21

We sought evidence for the involvement of mutations in the amyloid precursor protein gene (APP) in the pathogenesis of schizophrenia in two ways. First, linkage analysis was performed in a sample of 24 families multiply affected with schizophrenia. The genotypes were studied for GT12 (D21S210), a highly polymorphic microsatellite marker at the APP locus. Second, we used single strand conformation analysis (SSCA) to screen for mutations in exon 17 of APP in one affected member from each family and in a sample of 44 unrelated patients. In addition, we looked for linkage between schizophrenia and a series of highly polymorphic markers situated at approximately 20cM intervals along the long arm of chromosome 21. We were unable to find evidence for linkage to GT12 or the other markers studied. SSCA did not reveal any mutations in exon 17 of AP. We conclude that mutations within APP are an unlikely cause of schizophrenia. Moreover, this study provides no evidence for a major gene for schizophrenia on chromosome 21, and linkage can be excluded from much of this region under some genetic models.

The dopamine D3 receptor gene: no association with bipolar affective disorder

Bipolar affective disorder and schizophrenia share many clinical and genetic characteristics, and are thought by some to be different expressions of the same underlying disorder. A recent study showed an excess of homozygosity at a BalI polymorphism in the dopamine D3 receptor gene in schizophrenic patients compared with controls, from two independent centres. We have found no evidence of such an excess in a comparable sample of patients with bipolar affective disorder compared with matched controls. If these findings are confirmed then at least one genetic distinction between these two disorders will have been ascertained and doubt cast upon theories of a common genetic aetiology.

Association between schizophrenia and homozygosity at the dopamine D3 receptor gene

Disturbances in dopamine neurotransmission have been postulated to underlie schizophrenia. We report data from two independent studies of a BalI polymorphism in the dopamine D3 receptor gene in patients with schizophrenia. In both studies, more patients than controls were homozygous (p = 0.005, p = 0.008). When pooled data were analysed, this difference was highly significant (p = 0.0001) with a relative risk of schizophrenia in homozygotes of 2.61 (95% confidence intervals 1.60-4.26).

A linkage study of schizophrenia with DNA markers from the long arm of chromosome 11

We report the results of a collaborative linkage study using 12 polymorphic markers (9 loci) from the long arm of chromosome 11, and 24 families multiply affected with schizophrenia and other closely related disorders. This region is of interest because several families have been reported in which balanced translocations involving 11q apparently co-segregate with psychotic illness. In addition, the dopamine D2 receptor, porphobilinogen deaminase, and tyrosinase genes map within the region studied and may be aetiologically involved in schizophrenia. We have primarily analysed genotypic data by the LOD score method using a range of single gene models. In order to minimize error due to mis-specification of genetic parameters we have analysed data from markers at candidate gene loci by the non-parametric extended sib-pair method in addition to the LOD score method. Our results suggest that most of the region can be excluded from containing a gene of major effect in the aetiology of this disease.

No association between RFLPs at the porphobilinogen deaminase gene and schizophrenia

An association study of restriction fragment length polymorphisms (RFLPs) in the porphobilinogen deaminase (PBGD) gene and schizophrenia was conducted. RFLPs detected by MspI, PstI, ApaLI and BstNI in intron 1 of the gene were studied in 49 patients and 79 controls. There were no significant differences between the groups in allele frequencies, genotype counts or haplotype distribution.

Mononucleotide repeat polymorphism in the APP gene

Images