Clinical features of schizophrenia and linkage to chromosomes 5q, 6p, 8p, and 10p in the Irish Study of High-Density Schizophrenia Families

Schizophrenia is clinically heterogeneous. Recent linkage studies suggest that multiple genes are important in the etiology of schizophrenia. The authors examined the hypothesis of whether the clinical variability in schizophrenia is due to genetic heterogeneity.

Severe aplastic anaemia in association with a unique constitutional translocation 46,XY,t(6;10)(q13;q22)c

Severe aplastic anaemia (SAA) is an uncommon disorder which may be associated with several congenital syndromes. However, it has rarely been described in association with a constitutional karyotypic abnormality. The breakpoint of the balanced t(6:10)(q13:q22) translocation described here does not disrupt any currently recognized gene of haemopoietic or stromal importance. This report also highlights the problems inherent in the use of bone marrow transplantation (BMT) for treating multiply transfused aplastic anaemia patients.

A schizophrenia locus may be located in region 10p15-p11

In our genomic scan of 265 Irish families with schizophrenia, we have thus far generated modest evidence for the presence of vulnerability genes in three chromosomal regions, i.e., 5q21-q31, 6p24-p22, and 8p22-p21. Outside of those regions, of all markers tested to date, D10S674 produced one of the highest pairwise heterogeneity lod (H-LOD) scores, 3.2 (P = 0.0004), when initially tested on a subset of 88 families. We then tested a total of 12 markers across a region of 32 centimorgans in region 10p15-p11 of all 265 families. The strongest evidence for linkage occurred assuming an intermediate phenotypic definition, and a recessive genetic model. The largest pairwise H-LOD score was found with marker D10S2443 (maximum 1.95, P = 0.005). Using multipoint H-LODs, we found a broad peak (maximum 1.91, P = 0.006) extending over the 11 centimorgans from marker D10S674 to marker D10S1426. Multipoint nonparametric linkage analysis produced a much broader peak, but with the maximum in the same location near D10S2443 (maximum z = 1.88, P = 0.03). Based on estimates from the multipoint analysis, this putative vulnerability locus appears to be segregating in 5-15% of the families studied, but this estimate should be viewed with caution. When evaluated in the context of our genome scan results, the evidence suggests the possibility of a fourth vulnerability locus for schizophrenia in these Irish families, in region 10p15-p11.

Genetic variation in the 6p22.3 gene DTNBP1, the human ortholog of the mouse dysbindin gene, is associated with schizophrenia

Prior evidence has supported the existence of multiple susceptibility genes for schizophrenia. Multipoint linkage analysis of the 270 Irish high-density pedigrees that we have studied, as well as results from several other samples, suggest that at least one such gene is located in region 6p24-21. In the present study, family-based association analysis of 36 simple sequence-length-polymorphism markers and of 17 SNP markers implicated two regions, separated by approximately 7 Mb. The first region, and the focus of this report, is 6p22.3. In this region, single-nucleotide polymorphisms within the 140-kb gene DTNBP1 (dystrobrevin-binding protein 1, or dysbindin) are strongly associated with schizophrenia. Uncorrected, empirical P values produced by the program TRANSMIT were significant (P

Marker-to-marker linkage disequilibrium on chromosomes 5q, 6p, and 8p in Irish high-density schizophrenia pedigrees

Linkage disequilibrium (LD) is a potentially powerful tool for the localization of disease genes for complex disorders. Most prior studies of the relationship between genetic distance and LD have examined only very short distances, focusing on the role of LD in fine-mapping and positional cloning. We examine here the relationship between marker-to-marker (M-M) LD and somewhat greater genetic distances. We analyzed 622 M-M pairings on chromosomes 6p, 8p, and 5q in 265 native Irish pedigrees ascertained for a high density of schizophrenia. LD, significant at the 5% level, was found for 96% of all M-M pairings within 0.5 cM, for 67% within 0.5-1 cM, for 35% within 1-2 cM, for 15% within 2-4 cM, for 8% within 5-10 cM, and for 7% above 10 cM. Thus, in Irish families selected for a high density of schizophrenia, M-M LD may be very common within 0.5 cM and frequent up to distances of 2 cM.

The incidences of trisomy 8, trisomy 9 and D20S108 deletion in polycythaemia vera: an analysis of blood granulocytes using interphase fluorescence in situ hybridization:an analysis of blood granulocytes using interphase fluorescence in situ hybridization

We have used interphase fluorescence in situ hybridization (IFISH) to detect trisomy 8, trisomy 9 and 20q deletion in circulating granulocytes from patients with polycythaemia vera (PV). Out of 64 PV patients, 15 (23%) exhibited an abnormality. Two patients had trisomy 9, three had trisomy 8 and 10 patients had hemizygous deletion of D20S108 (a locus in the 20q common deleted region). Aberrant nuclei ranged from 10% to 80% in these 15 cases. There was no correlation between the presence of a marker and sex, age, interval between presentation and IFISH analysis, neutrophil or platelet count or therapy. Conventional marrow cytogenetic karyotype results were available in 23 cases and there was concurrence between these and blood IFISH in 16 cases (13 normal and three with 20q/D20S108 deletion by both methods). Three patients with D20S108 deletion by IFISH were normal by previous marrow cytogenetic testing and four cases with 20q deletion by previous marrow cytogenetics had normal blood granulocytes according to IFISH. Thus, we confirm that trisomies 8 and 9 and deletion of 20q are diagnostically useful markers of PV. IFISH analysis of blood granulocytes is a practical method for detecting these markers, but as an adjunct to, not as a substitute for, conventional marrow cytogenetics.

Dual-colour HER2/chromosome 17 chromogenic in situ hybridisation enables accurate assessment of HER2 genomic status in ovarian tumours

Ovarian cancer is a leading cause of gynaecological cancer-related morbidity and mortality. There has been increasing interest in the potential utility of anti-human epidermal growth factor receptor 2 (anti-HER2) agents in the treatment of this disease, with the attendant need to identify suitable predictive biomarkers of response to treatment.

Dual-colour HER2/chromosome 17 chromogenic in situ hybridisation assay enables accurate assessment of HER2 genomic status in gastric cancer and has potential utility in HER2 testing of biopsy samples

Determination of HER2 protein expression by immunohistochemistry (IHC) and genomic status by fluorescent in situ hybridisation (FISH) are important in identifying a subset of high HER2-expressing gastric cancers that might respond to trastuzumab. Although FISH is considered the standard for determination of HER2 genomic status, brightfield ISH is being increasingly recognised as a viable alternative. Also, the impact of HER2 protein expression/genomic heterogeneity on the accuracy of HER2 testing has not been well studied in the context of gastric biopsy samples.

A potential vulnerability locus for schizophrenia on chromosome 6p24-22:evidence for genetic heterogeneity

In 265 Irish pedigrees, with linkage analysis we find evidence for a vulnerability locus for schizophrenia in region 6p24-22. The greatest lod score, assuming locus heterogeneity, is 3.51 (P = 0.0002) with D6S296. Another test, the C test, also supported linkage, the strongest results being obtained with D6S296 (P = 0.00001), D6S274 (P = 0.004) and D6S285 (P = 0.006). Non-parametric analysis yielded suggestive, but substantially weaker, findings. This locus appears to influence the vulnerability to schizophrenia in roughly 15 to 30% of our pedigrees. Evidence for linkage was maximal using an intermediate phenotypic definition and declined when this definition was narrowed or was broadened to include other psychiatric disorders.

Support for a possible schizophrenia vulnerability locus in region 5q22-31 in Irish families

In our genome scan for schizophrenia genes in 265 Irish pedigrees, marker D5S818 in 5q22 produced the second best result of the first 223 markers tested (P = 0.002). We then tested an additional 13 markers and the evidence suggests the presence of a vulnerability locus for schizophrenia in region 5q22-31. This region appears to be distinct from those chromosome 5 regions studied in two prior reports, but the same as that producing positive results in the report by Wildenauer and colleagues found elsewhere in this issue. The largest pairwise heterogeneity LOD (H-LOD) score was found with marker D5S393 (max 3.04, P = 0.0005), assuming a narrow phenotypic category, and a genetic model with intermediate heterozygotic liability. In marked contrast to the H-LOD scores from our sample with markers from the regions of interest on chromosomes 6p and 8p, expanding the disease definition to include schizophrenia spectrum or nonspectrum disorders produced substantially smaller scores, with a number of markers failing to yield positive values at any recombination fraction. Using multipoint H-LODS, the strongest evidence for linkage occurs under the narrow phenotypic definition and recessive genetic model, with a peak at marker D5S804 (max 3.35, P = 0.0002). Multipoint nonparametric linkage analysis produced a peak in the same location (max z = 2.84, P = 0.002) with the narrow phenotypic definition. This putative vulnerability locus appears to be segregating in 10-25% of the families studied, but this estimate is tentative. Comparison of individual family multipoint H-LOD scores at the regions of interest on chromosomes 6p, 8p and 5q showed that only a minority of families yield high lod scores in two or three regions.

No major schizophrenia locus detected on chromosome 1q in a large multicenter sample

Reports of substantial evidence for genetic linkage of schizophrenia to chromosome 1q were evaluated by genotyping 16 DNA markers across 107 centimorgans of this chromosome in a multicenter sample of 779 informative schizophrenia pedigrees. No significant evidence was observed for such linkage, nor for heterogeneity in allele sharing among the eight individual samples. Separate analyses of European-origin families, recessive models of inheritance, and families with larger numbers of affected cases also failed to produce significant evidence for linkage. If schizophrenia susceptibility genes are present on chromosome 1q, their population-wide genetic effects are likely to be small.

No evidence for linkage or association of neuregulin-1 (NRG1) with disease in the Irish study of high-density schizophrenia families (ISHDSF)

The neuregulin-1 gene (NRG1) at chromosome 8p21-22 has been implicated as a schizophrenia susceptibility gene in Icelandic, Scottish, Irish and mixed UK populations. The shared ancestry between these populations led us to investigate the NRG1 polymorphisms and appropriate marker haplotypes for linkage and/or association to schizophrenia in the Irish study of high-density schizophrenia families (ISHDSF). Neither single-point nor multi-point linkage analysis of NRG1 markers gave evidence for linkage independent of our pre-existing findings telomeric on 8p. Analysis of linkage disequilibrium (LD) across the 252 kb interval encompassing the 7 marker core Icelandic/Scottish NRG1 haplotype revealed two separate regions of modest LD, comprising markers SNP8NRG255133, SNP8NRG249130 and SNP8NRG243177 (telomeric) and microsatellites 478B14-428, 420M9-1395, D8S1810 and 420M9-116I12 (centromeric). From single marker analysis by TRANSMIT and FBAT we found no evidence for association with schizophrenia for any marker. Haplotype analysis for the three SNPs in LD region 1 and, separately, the four microsatellites in LD region 2 (analyzed in overlapping 2-marker windows), showed no evidence for overtransmission of specific haplotypes to affected individuals. We therefore conclude that if NRG1 does contain susceptibility alleles for schizophrenia, they impact quite weakly on risk in the ISHDSF.

Relationship between a high-risk haplotype in the DTNBP1 (dysbindin) gene and clinical features of schizophrenia

The purpose of this study was to determine whether a haplotype in the dystrobrevin binding protein 1 (DTNBP1) gene previously associated with schizophrenia not only increases the susceptibility to psychotic illness but also to a more or less clinically specific form of psychotic illness.

Haplotypes spanning SPEC2, PDZ-GEF2 and ACSL6 genes are associated with schizophrenia

Chromosome 5q22-33 is a region where studies have repeatedly found evidence for linkage to schizophrenia. In this report, we took a stepwise approach to systematically map this region in the Irish Study of High Density Schizophrenia Families (ISHDSF, 267 families, 1337 subjects) sample. We typed 289 SNPs in the critical interval of 8 million basepairs and found a 758 kb interval coding for the SPEC2/PDZ-GEF2/ACSL6 genes to be associated with the disease. Using sex and genotype-conditioned transmission disequilibrium test analyses, we found that 19 of the 24 typed markers were associated with the disease and the associations were sex-specific. We replicated these findings with an Irish case-control sample (657 cases and 414 controls), an Irish parent-proband trio sample (187 families, 564 subjects), a German nuclear family sample (211 families, 751 subjects) and a Pittsburgh nuclear family sample (247 families, 729 subjects). In all four samples, we replicated the sex-specific associations at the levels of both individual markers and haplotypes using sex- and genotype-conditioned analyses. Three risk haplotypes were identified in the five samples, and each haplotype was found in at least two samples. Consistent with the discovery of multiple estrogen-response elements in this region, our data showed that the impact of these haplotypes on risk for schizophrenia differed in males and females. From these data, we concluded that haplotypes underlying the SPEC2/PDZ-GEF2/ACSL6 region are associated with schizophrenia. However, due to the extended high LD in this region, we were unable to distinguish whether the association signals came from one or more of these genes.

Association between the 5q31.1 gene neurogenin1 and schizophrenia

Multiple lines of evidence suggest that schizophrenia results from aberrant neurodevelopment. The neurogenin1 gene (neurog1) consists of a single 1,666 bp exon that encodes a basic helix-loop-helix (bHLH) transcription factor that causes neuronal differentiation and induces cortical and glutamatergic differentiation programs. Because of its function and its location in 5q31.1, which has been linked to schizophrenia in multiple samples, we tested it for association with the disorder. We sequenced neurog1 in 25 affected subjects from the Irish Study of High-Density Schizophrenia Families. We observed a 5'-UTR SNP at position -60, already present in databases as rs8192558, and tested it along with rs2344485, rs8192559, and rs2344484. Narrow, intermediate, and broad diagnostic definitions were used. The major alleles of rs8192558 and rs2344484 were over-transmitted to affected subjects using both Pedigree Disequilibrium Test (PDT) (0.01 <or = P <or = 0.06) and FBAT (0.02 <or = P <or = 0.07). A haplotype consisting of the major alleles of all four SNPs was significantly over-transmitted in FBAT to the broad definition (P = 0.049), with trend significance to the narrow and intermediate definitions, and with trend significance in PDT. In confirmatory tests using 657 cases and 411 controls, this haplotype was slightly but not significantly over-represented in cases (81% vs. 77%, P = 0.21). These results, along with a priori evidence for the involvement of neurog1 in neurodevelopment, suggest that variants in neurog1 might have a small effect on susceptibility to schizophrenia. This gene should be tested in additional and larger samples.