Kathryn L. Evans

Markers close to the dopamine D5 receptor gene (DRD5) show significant association with schizophrenia but not bipolar disorder

Following the description of linkage of markers at chromosome 4p16 to bipolar disorder in several families [Blackwood et al., 1996], and the association of the alleles of a polymorphism closely linked to D5 dopamine receptor gene with schizophrenia [Williams et al., 1997], we have looked for linkage disequilibrium between a series of microsatellite markers from this region and major psychoses including schizophrenia, bipolar disorder, and unipolar major depressive disorder. A significant increase in the frequency of the 148 bp allele of DRD5 (P = 0.024) and the 244 bp allele of D4S615 (P = 0.001) was found in patients with schizophrenia (n = 158 DRD5; n = 133 D4S615), compared with patients with bipolar disorder (n = 270 DRD5; n = 107 D4S615), or controls without psychiatric illness (n = 437 DRD5; n = 309 D4S615). The frequency of the 148 bp allele of DRD5 was also increased in schizophrenia over unipolar major depressive disorder (n = 65). D4S615 was not typed in unipolar disorder. The estimated odds ratios confirmed that the 148 bp allele of DRD5 and the 244 bp allele of D4S615 conferred increased risk of schizophrenia. Estimated Haplotype (EH) analysis of 174 controls and 128 patients with schizophrenia who were typed for both markers confirmed the strong associations with these alleles but did not show evidence that the markers were in linkage disequilibrium with each other even though they lie approximately 150 kb apart. The data are consistent with an association between markers close to the D5 dopamine receptor and schizophrenia, but not bipolar disorder or unipolar major depression.

Mutational analysis of the Wolfram syndrome gene in two families with chromosome 4p-linked bipolar affective disorder.

Bipolar affective disorder (BPAD) is a complex disease with a significant genetic component. Heterozygous carriers of Wolfram syndrome (WFS) are at increased risk of psychiatric illness. A gene for WFS (WFS1) has recently been cloned and mapped to chromosome 4p, in the general region we previously reported as showing linkage to BPAD. Here we present sequence analysis of the WFS1 coding sequence in five affected individuals from two chromosome 4p-linked families. This resulted in the identification of six polymorphisms, two of which are predicted to change the amino acid sequence of the WFS1 protein, however none of the changes segregated with disease status. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:158-160, 2000.

Nuts and bolts of psychiatric genetics: building on the Human Genome Project

Schizophrenia and bipolar affective disorder are chronic, disabling illnesses that together affect 2% of the population. Genetic factors are known to be important in their development, but there are, as yet, no confirmed susceptibility genes. Here we discuss important issues in terms of alternative genetic strategies (linkage, association and/or cytogenetics) in the identification of candidate genes for the major psychoses. We discuss the impact of the Human Genome Project, the role of comparative genetics in finding and testing positional candidates, and the prospects for rational drug design and personalized medicine.

Chromosome 4 Workshop summary : Sixth World Congress on Psychiatric Genetics, Bonn, Germany, October 6-10, 1998

This report summarizes the findings presented at the Chromosome 4 Workshop of the Sixth World Congress on Psychiatric Genetics (October 1998, Bonn, Germany). Chromosome 4 linkage and association results for several psychiatric phenotypes including bipolar affective disorder, schizophrenia, alcoholism, and mental retardation are reviewed. In bipolar affective disorder, positive linkage results for markers on 4q35 were reported by three independent groups. In addition, findings in bipolar disorder were reported for markers spanning 4p14-16, and of particular interest are the results that coincide with the original Blackwood et al. [1996: Nat Genet 12:427-430] region at 4p16. For schizophrenia, modest positive results were reported for 4q31, as well as for marker D4S2917 at a region of 4q close to the centromere. Chromosome 4 continues to demonstrate interesting results in alcoholism, particularly in the region of the alcohol dehydrogenase gene cluster; however, it is not clear how to interpret the contrast in the susceptibility versus protective loci that are being reported in this region.

Novel transcribed sequences neighbouring a translocation breakpoint associated with schizophrenia

A 1.3Mb chromosome 11-specific yeast artificial chromosome (YAC) that spans a t(1;11) translocation breakpoint associated with major psychosis has been used to enrich cDNAs that are encoded within it and expressed in the human foetal brain. Database analysis of the selected fragments led to the identification of 54 clones matching alpha-tubulin, 4 fragments matching two anonymous human expressed sequence tags (ESTs) and 8 fragments giving no database matches. The clones matching alpha-tubulin led to the identification of a novel alpha-tubulin locus located approximately 250 kb proximal to the translocation breakpoint. Extensive sequence and expression analysis of this locus suggests that this is a processed pseudogene, although a long open reading frame is maintained and the possibility that an abnormally acting protein may be expressed in a highly tissue or developmental specific manner cannot be discounted. The novel cDNA fragments map up to 700 kb proximal to the translocation breakpoint and are associated with potential CpG islands. Reverse transcriptase polymerase chain reaction (RT-PCR) expression analysis and high resolution genomic mapping suggest that they may comprise up to three novel genes. No major disruption of the identified fragments could be detected in the genomic DNA of translocation carriers. The psychosis associated with this translocation may therefore be due to position effects on the transcription of these genes or an involvement of translocated chromosome 1 sequences.

Overexpression of CDC25A associated with poor prognosis in breast cancer

Cell-cycle regulation is often altered in cancer; mutations cause the abolition of cell-cycle checkpoints resulting in uncontrolled cell proliferation. The cell-cycle gene, CDC25A, activates cyclin-dependent kinase 2 (CDK2), promoting entry into S (DNA synthesis) phase of the cell cycle. Overexpression of CDC25A, which has been shown previously to have oncogenic potential, eliminates this checkpoint. Cangi and colleagues1xRole of the Cdc25A phosphatase in human breast cancer. Cangi, M.G. et al. J. Clin. Invest. 2000; 106: 753–761Crossref | PubMed | Scopus (150)See all References examined primary breast tumours samples and found that CDC25A was overexpressed in,50% of those tested. This overexpression was associated with abnormally increased CDK2 activity, in the absence of any increase in CDK2 protein production. CDC25A was then inactivated in a breast cancer cell line by transfection with CDC25A antisense oligos. This treatment blocked CDK2 activation, without affecting CDK2 protein levels, showing that CDC25A was responsible for the increase in CDK2 activity. Cangi et al. further investigated whether CDC25A overexpression is associated with outcome in 144 patients with breast carcinomas of,1 cm diameter, who tend to have a good prognosis. Patients with tumours that overexpressed CDC25A had an increased risk of dying of the disease (24% mortality vs 5% mortality in patients with tumours that did not express CDC25A). The results of this study suggest that it might be useful to measure CDC25A and CDK2 levels before designing treatment regimes, and that CDC25A and CDK2 represent promising therapeutic targets for breast cancer treatment.

Identifying genes within microdissected genomic DNA: Isolation of brain expressed genes from a translocation region associated with inherited mental illness

An improved protocol has been developed for physical enrichment of cDNA sequences by hybridization to genomic DNA. When applied to microdissection recombinants derived from a translocation breakpoint region associated with inherited mental illness, a single cycle of the procedure permitted enriched cDNAs to be visualized directly by agarose gel electrophoresis. Hybridization screening of a library of clones derived from the enriched cDNAs, employing the genomic resource as a probe, led to the identification of six novel gene fragments. This general approach to the isolation of regionally encoded genes could be applied to any subchromosomal interval as a first step towards global transcription map construction.

A schizophrenic mouse

N-methyl-d-aspartate receptor (NMDAR) deficiency has been suggested as a possible cause of schizophrenia. In part, this is because intoxication with three different non-competitive antagonists of NMDARs [phencyclidine (PCP), MK-801 and ketamine] mimics the disorder.Mohn et al.1xMice with reduced NMDA receptor expression display behaviors related to schizophrenia. Mohn, A.R. et al. Cell. 1999; 98: 427–436Abstract | Full Text | Full Text PDF | PubMed | Scopus (715)See all References1 have studied the effect of NMDAR deficiency on murine behaviour. NMDAR complexes consist of one NMDAR subunit 1 (NR1) and one of four NR2 subunits. Mice that lack the NR1 protein die perinatally, so Mohn et al. generated, by insertional mutagenesis, a strain of mice in which NR1 is expressed at only 5–10% of wild-type levels. Although this was found to be sufficient for survival, the mice displayed hyperlocomotion, increased stereotypic behaviour and social withdrawal, which are believed to mirror behaviours seen in schizophrenia. Treatment with the atypical antipsychotic drug clozapine, which treats schizophrenic symptoms without causing severe side effects, reduced the locomotion and stereotypy in the NMDAR-deficient mice to wild-type levels and decreased the levels of social withdrawal; the behaviour of wild-type mice was not affected by the treatment. In addition, PCP and MK-801 had no effect on the NMDAR-deficient mice, suggesting that the behavioural effects of these compounds are mediated through suppression of NMDARs.This work has provided insight into a possible mechanism for some aspects of schizophrenia. In addition, it will allow the study of the effect of long-term NMDAR deficiency, which is important because schizophrenia is thought to be a progressive mental illness.

Clues to the causes of neurodegeneration

Neurodegeneration is a feature of a number of disorders, for example Alzheimer’s and Parkinson’s diseases, that have a significant impact on public health. Although there are a number of plausible hypotheses, the cause of neuronal death in these types of disorders is unknown. Lin and colleagues1xPolyglutamine expansion down-regulates specific neuronal genes before pathologic changes in SCA1. Lin, X. et al. Nat. Neurosci. 2000; 3: 157–163Crossref | PubMed | Scopus (354)See all References1 have identified early events that might result in neuronal death in the neurodegenerative disorder spinocerebellar ataxia type 1 (SCA1).SCA1 is an autosomal dominant disease in which the mutant protein apparently acquires a new, toxic function that results in cell death. Previous work on SCA1 mouse models has shown that nuclear localization of the mutant protein is essential to the development of SCA1-like symptoms. This requirement led Lin and colleagues to hypothesize that the mutant protein acts by altering transcription. Therefore, the group used a PCR-based cDNA subtractive-hybridization strategy to analyse gene expression in two mouse lines transgenic for SCA1 cDNAs with expanded glutamine tracts. It was found that one neuronal cDNA was upregulated, and six were downregulated, in both lines, relative to controls. Whereas the upregulation occurred at a later stage in disease development, the downregulation occurred very soon after transgene expression, well before any behavioural or pathological signs appeared, indicating that these changes happen very early in the disease process. The downregulated genes are involved in glutamate metabolism and calcium homeostasis, suggesting that alterations in these systems might be important in the subsequent neuronal death.There are, however, important questions that remain unanswered. For example, how does the mutant protein affect gene expression; do the changes lead to neuronal death (and if so, by what mechanism); does this scenario apply to other neurodegenerative disorders and, finally, can treatments aimed at preventing or ameliorating the effects of downregulation of these genes be developed?

Reversal of leukaemia

Cancer is generally the end result of multiple genetic events that cause irreversible malignancy. However, this might not be the case in some leukaemias that are associated with balanced translocations. Transgenic animals provide an ideal system in which to study the effects of gene fusion products that are generated by translocations.Huettner and colleagues1xReversibility of acute B-cell leukaemia induced by BCR-ABL1. Huettner, C.S. et al. Nat. Genet. 2000; 24: 57–60Crossref | PubMed | Scopus (299)See all References1 have created a transgenic mouse in which expression of a BCR-ABL1 oncogene, which is a causative agent in 90% of chronic myelogenous leukaemia (CML) and up to 15% of adults with de novo acute lymphoblastic leukaemia (ALL), can be turned on or off in a specific cell type in the adult animal. Expression of this oncogene resulted in acute B-cell leukaemia in 100% of animals from four different transgenic lines. However, when the gene was switched off, all animals exhibited reversal of the phenotype, including those with advanced disease. Remission was permanent in 100% of animals from three of the lines, but all animals from the fourth line developed a rapidly progressing B-cell leukaemia that was independent of BCR-ABL1 expression. This line had taken much longer than the others to develop the initial B-cell leukaemia, perhaps implying that there had been more time for secondary mutations to accumulate.This work is important, as it shows both that continued expression of this oncogene is necessary for the maintenance of cancer in vivo and that the phenotype can be completely reversed, even at an advanced stage. The results suggest that drugs that inhibit leukaemic oncogenes should provide very effective therapy in this disease, and that this model is an excellent system for the testing of such drugs. Finally, it will be interesting to see whether this mechanism applies to other translocation associated leukaemias.