Gaynor Jones

A systematic genomewide linkage study in 353 sib pairs with schizophrenia

We undertook a genomewide linkage study in a total of 353 affected sib pairs (ASPs) with schizophrenia. Our sample consisted of 179 ASPs from the United Kingdom, 134 from Sweden, and 40 from the United States. We typed 372 microsatellite markers at approximately 10-cM intervals. Our strongest finding was a LOD score of 3.87 on chromosome 10q25.3-q26.3, with positive results being contributed by all three samples and a LOD-1 interval of 15 cM. This finding achieved genomewide significance (P<.05), on the basis of simulation studies. We also found two regions, 17p11.2-q25.1 (maximum LOD score [MLS] = 3.35) and 22q11 (MLS = 2.29), in which the evidence for linkage was highly suggestive. Linkage to all of these regions has been supported by other studies. Moreover, we found strong evidence for linkage (genomewide P<.02) to 17p11.2-q25.1 in a single pedigree with schizophrenia. In our view, the evidence is now sufficiently compelling to undertake detailed mapping studies of these three regions.

Polymorphisms in the MAOA, MAOB, and COMT genes and aggressive behavior in schizophrenia

Some studies have reported associations between COMT and MAO genotypes and aggression, though results have been inconsistent. We examined the relationship between Overt aggression scale (OAS) scores, and both MAOA and MAOB polymorphisms in a well‐powered sample of 346 subjects with schizophrenia. We also examined COMT in a Stage II replication sample of 150 individuals, and combined these results with our previously reported (Stage I) findings for COMT. We found no evidence of any associations between OAS ratings and any of the polymorphisms investigated under different genetic models. There was no evidence of epistatic interaction between MAOA and COMT on OAS scores. These results fail to support the theory that functional polymorphisms within the MAOA, MAOB, or COMT genes, as determinants of catecholamine enzymatic activity, are risk factors for aggressive behavior.

Mutation screening of the Homer gene family and association analysis in schizophrenia

Homer proteins are a group of proteins that regulate group 1 metabotropic glutamate receptor function. As altered glutamate function has been implicated in many neuro psychiatric disorders, particularly schizophrenia, we have screened all three known Homer genes for sequence variation for use under the candidate gene association paradigm. We found seven SNPs, including three in exons. Of these, none was non‐synonymous. Allele frequencies of all the detected SNPs were estimated in DNA pools of 368 schizophrenics and 368 controls. Only one (Homer 1 IVS4 + 18A > G) was associated with schizophrenia in this sample, a finding confirmed by individual genotyping (P = 0.01). However, in our extended sample of 680 cases and 671 controls, the evidence for association diminished (P = 0.05). Our results suggest it is unlikely that sequence variants in the Homer genes contribute to the aetiology of schizophrenia, but the variants we identified are plausible candidates for other neuropsychiatric phenotypes.

Characterisation, mutation detection, and association analysis of alternative promoters and 5’UTRs of the human dopamine D3 receptor gene in schizophrenia

The dopamine D3 receptor gene (DRD3) is a candidate for a number of psychiatric conditions including schizophrenia, bipolar disorder and alcohol and drug abuse. Previous studies have reported associations between polymorphisms in DRD3 and these disorders, but these findings may have reflected linkage disequilibrium with pathogenic variants that are further upstream. We have isolated and sequenced approximately 9 kb of genomic sequence upstream of the human DRD3 translational start site. Using 5′ RACE, we have identified within this region three additional exons and two putative promoter regions which show promoter activity in three different cell lines. A 5′ UTR identified only in lymphoblasts is spread over three exons and is 353 bp long. A second 5′ UTR, found in adult and fetal brain, lymphocytes, kidney and placenta is spread over two exons and is 516 bp long. A 260-bp sequence within this 9 kb corresponds to a previously reported EST, but corresponding mRNA could not be found in the tissues above. The EST, 5′ UTRs and putative promoter regions have been analysed for polymorphisms, revealing 10 single nucleotide polymorphisms, seven of which were tested for association in a large sample of unrelated patients with schizophrenia and matched controls. No associations were observed with schizophrenia. In addition we failed to replicate previous findings of association with homozygosity of the Ser9Gly variant. The results from this study imply that neither the coding nor the regulatory region of DRD3 plays a major role in predisposition to schizophrenia.

Mutation screening of the KCNN3 gene reveals a rare frameshift mutation

259 posing an a of 0.05 with 18 patients (homozygous insertion), a satisfactory power of 0.84 was reached. Demographic, genetic and clinical data are summarised in Table 1. We were unable to replicate the previous finding since we observed no significant differences in genotype or allelic distributions between patients and controls (both followed the Hardy–Weinberg Equilibrium). Ethnic differences or differences in patient selection between both studies might be responsible for these discrepancies. No significant differences in genotypes or allele frequencies were found with respect to treatment procedures. A divergent clinical outcome was observed in that, after 4 weeks of treatment, D-allele carriers showed significantly lower HAM-D17 scores (P , 0.0001), remitted more often (HAM-D17 ,9; D/D+I/D:I/I = 18:1; P = 0.049) and had a significantly shorter duration of hospitalisation (P = 0.020). Also, the number of treatment alterations during hospitalisation was significantly higher in I/I-genotypes. Thus, the Dallele might positively influence the onset of therapeutic efficacy. Homozygosity for the I-allele seems to be associated with delayed response. Since, in functional studies, ACE allele-D was associated with increased neuropeptide degradation, increased SP concentrations might be responsible for the delayed effect on I/I-genotypes. This, however, has not yet been proven; SP levels were not controlled in this study and the role of SP in the treatment of depression still has to be clarified. Although therapeutic outcome in different genotypes cannot yet be related to the diversity of medication, our results give first hints that variants in the ACE gene could contribute to differential drug response. Further studies will have to clarify whether this effect is related to different drugs or a common feature of antidepressant treatment. In addition to association studies, family studies might help to further clarify the relationship between treatment response as a complex phenotype and ACE gene polymorphism.

The high affinity neurotensin receptor gene (NTSR1): comparative sequencing and association studies in schizophrenia

Neurotensin and its high affinity receptor (NTSR1) localise within dopaminergic neurones in the mesocortical, mesolimbic and nigrostriatal systems1, 2, 3, 4, 5 and it is now clear that neurotensin can selectively modulate dopaminergic neurotransmission.2, 3, 6, 7, 8, 9, 10, 11 This has led to the hypothesis that altered neurotensin function contributes to the pathogenesis of schizophrenia and other psychoses. This hypothesis has been supported circumstantially by a number of lines of evidence. (1) Central administration of neurotensin produces effects similar to those produced by the peripheral administration of atypical antipsychotics.12, 13, 14, 15 (2) Observations of low levels of neurotensin in the CSF of schizophrenics.16, 17 (3) Reduced numbers of neurotensin receptors in the brains of schizophrenics.18, 19 Given the above link between neurotensin and dopamine, and the evidence implicating altered neurotensin function in psychosis, we20 have postulated that DNA sequence variation in neurotensin or its receptors might be associated with schizophrenia. In keeping with this hypothesis, an association has recently been reported21 between schizophrenia and the gene encoding the neurotensin high affinity receptor (NTSR1). However, caution is required because the associated marker, a tetranucleotide repeat, is located 3 kb away from the 3′ end of the gene and there is no evidence that it is functional. Therefore, as a follow-up to our earlier work on neurotensin,20 we have now sought to test the hypothesis that DNA sequence variants that alter the structure or expression of the NTSR1 gene (VAPSEs)22 are associated with schizophrenia. However, while we found 14 novel sequence variants in 28 probands with psychosis, none resulted in an amino acid change, and neither direct nor indirect association studies suggested these are involved in susceptibility to schizophrenia.

Genome wide significant linkage in schizophrenia conditioning on occurrence of depressive episodes.

Background: Schizophrenia shows substantial clinical heterogeneity. One common important clinical variable in presentation is the occurrence of episodes of major depression. Methods: We undertook analyses in an attempt to detect loci that influence susceptibility to, or modify the clinical expression of, schizophrenia according to the occurrence of episodes of major depression. We used a logistic regression framework in which lifetime presence/absence of major depression was entered as a covariate in the linkage analysis of our UK schizophrenia affected sibling pair series (168 affected sibling pairs typed for a 10 cM map of microsatellite markers). Results: Inclusion of presence/absence of depression as a covariate detected a genome wide significant linkage signal on chromosome 4q28.3 at 130.7 cM (LOD = 4.59; p = 0.038; increase in maximum LOD over univariate analysis (ILOD) = 3.62). Inclusion of the depression covariate also showed suggestive evidence of linkage on 20q11.21 (LOD = 4.10; expected to occur by chance 0.093 times per genome scan, ILOD = 2.83). Conclusions: Our findings identify loci that may harbour genes that play a role in susceptibility to, or modify the risk of, episodes of major depression in people with schizophrenia.

Association analysis of the HOPA12bp polymorphism in schizophrenia and manic depressive illness

Variations in exon 42 of the HOPA (human opposite paired) gene have been associated with mental retardation, hypothyroidism and psychiatric disorders. We attempted to replicate the association with schizophrenia using 309 parent‐offspring trios from Bulgaria and 367 unrelated cases and 368 blood donors from the UK. We also tested 125 bipolar trios from Bulgaria, 112 bipolar trios from the UK and a sample of 178 unrelated bipolar cases and 188 blood donors from the UK. The frequency of HOPA12bp in the 556 UK blood donors was 2.6% and it was not significantly different in the UK patients groups, where it ranged from 1.2 to 3.8%. Sixteen mothers transmitted the HOPA12bp allele to schizophrenic offspring, while 12 did not transmit, a non‐significant difference. There was a trend for under‐transmission of the rare allele to bipolar patients (T/NT = 4/10) and they had a lower rate of that allele than schizophrenic patients in the Bulgarian population (1% vs. 4.2%, P = 0.043). However the two diagnostic groups had similar allele frequencies in the UK populations: 2% versus 2.6%, P = 0.6. We conclude that the HOPA polymorphism is unlikely to be a major risk factor in the pathogenesis of these major psychiatric disorders although there could be a small effect in schizophrenia.

Genetic variation in the seven-pass transmembrane cadherin CELSR1: lack of association with schizophrenia.

Objectives Cadherins play a critical role in morphogenesis and maintenance of neuronal connections in the adult brain. We examined the gene encoding a member of the non‐classic seven‐pass transmembrane cadherins, CELSR1 for association with schizophrenia. It maps to chromosome 22q13.31, a region in which evidence for linkage to schizophrenia has been reported. The gene has an unusually large first exon of 3544 nucleotides, which encodes the signal peptide and all nine ectodomains in the protein. Methods We screened this exon in 24 schizophrenic patients using denaturing high‐performance liquid chromatography followed by sequencing. Genotyping of aminoacid changes was performed with primer extension on a sample of 244 Bulgarian schizophrenic patients from 233 families and all their parents, as well as 180 schizophrenic patients from the UK and 157 controls. Results Three amino‐acid changes were identified and shown to be in complete linkage disequilibrium: L556 V, S664W and R1126C. There was no preferential transmission of alleles from heterozygous parents to affected offspring. In the UK population the rare alleles were even more common in controls, and this difference almost reached statistical significance for R1126C (&KHgr;2 = 3.63, P = 0.057). Conclusions We conclude that variations in the nine ectodomains of CELSR1 do not increase susceptibility to schizophrenia.

Genetic variation in the seven-pass transmembrane cadherin CELSR1

Objectives Cadherins play a critical role in morphogenesis and maintenance of neuronal connections in the adult brain. We examined the gene encoding a member of the non‐classic seven‐pass transmembrane cadherins, CELSR1 for association with schizophrenia. It maps to chromosome 22q13.31, a region in which evidence for linkage to schizophrenia has been reported. The gene has an unusually large first exon of 3544 nucleotides, which encodes the signal peptide and all nine ectodomains in the protein. Methods We screened this exon in 24 schizophrenic patients using denaturing high‐performance liquid chromatography followed by sequencing. Genotyping of aminoacid changes was performed with primer extension on a sample of 244 Bulgarian schizophrenic patients from 233 families and all their parents, as well as 180 schizophrenic patients from the UK and 157 controls. Results Three amino‐acid changes were identified and shown to be in complete linkage disequilibrium: L556 V, S664W and R1126C. There was no preferential transmission of alleles from heterozygous parents to affected offspring. In the UK population the rare alleles were even more common in controls, and this difference almost reached statistical significance for R1126C (&KHgr;2 = 3.63, P = 0.057). Conclusions We conclude that variations in the nine ectodomains of CELSR1 do not increase susceptibility to schizophrenia.