Anticipation in schizophrenia: no evidence of expanded CAG/CTG repeat sequences in French families and sporadic cases

A decrease in age of onset of schizophrenia through consecutive family generations (anticipation) has been found in several studies. Anticipation is known to result from expansion of CAG repeats in genes that determine several neurodegenerative disorders. In a previous study we analysed 26 unilineal two-generation French pedigrees and found clinical evidence of anticipation. A 10-year mean reduction in age of onset of schizophrenia was found in the second generation compared with the parental generation. The repeat expansion detection method was used to screen for CAG expansion in 21 of the 26 families with evidence of anticipation for the disease and in 59 sporadic schizophrenics and 59 controls. Comparison of the frequency distributions of CAG/CTG repeat size observed in schizophrenics and controls showed no significant difference, even when we considered familial (P = 0.23) and sporadic (P = 0.25) affected individuals separately. These results do not support the association between long CAG repeats and schizophrenia. However, the possibility that expansions with fewer than 40 repeats are involved in schizophrenia cannot be excluded.

Adenovirus in the brain: recent advances of gene therapy for neurodegenerative diseases

Adenovirus is an efficient vector for neuronal gene therapy due to its ability to infect post-mitotic cells, its high efficacy of cell transduction and its low pathogenicity. Recombinant adenoviruses encoding for therapeutical agents can be delivered in vivo after direct intracerebral injection into specific brain areas. They can be transported in a retrograde manner from the injection site to the projection cell bodies offering promising applications for the specific targeting of selected neuronal populations not easily accessible by direct injection, such as the motor neurons in the spinal cord. Adenoviral vectors are also efficient tools for the ex vivo gene therapy, that is, the genetical modification of cells prior to their transplantation into the nervous system. Recently, the efficacy of the adenovirus as a gene vector system has been demonstrated in several models of neurodegenerative diseases including Parkinson's disease (PD) and motor neuron diseases. In rat models of PD, adenoviruses encoding for either tyrosine hydroxylase, superoxide dismutase or glial-derived neurotrophic factor improved the survival and the functional efficacy of dopaminergic cells. Similarly, the intramuscular injection of an adenovirus encoding for neurotrophin-3 had substantial therapeutic effects in a mutant mouse model of motor neuron degenerative disease. However, although adenoviruses are highly attractive for neuronal gene transfer, they can trigger a strong inflammatory reaction leading in particular to the destruction of infected cells. The recent development of new generations of adenoviral vectors could shed light on the nature of the immune reaction caused by adenoviral vectors in the brain. The use of these new vectors, combined with that of neurospecific and regulatable promoters, should improve adenovirus gene transfer into the central nervous system.

Increase in syntaxin 1B and glutamate release in mossy fibre terminals following induction of LTP in the dentate gyrus: a candidate molecular mechanism underlying transsynaptic plasticity

A growing body of evidence suggests that modulation of certain proteins of the exocytotic machinery is, in part, involved in the biochemical changes that underlie long-term synaptic plasticity. We have previously shown that the induction of long-term potentiation (LTP) at perforant path to dentate granule cell synapses in the rat hippocampus induces changes in the mRNA levels of syntaxin 1B and synapsin I, known to be involved in neurotransmitter release. Immunohistochemical staining suggested that concomitant changes in these proteins occurred at mossy fibre synapses, downstream of those synapses at which LTP was induced, leading us to postulate that such a mechanism might underlie a form of transsynaptic plasticity. Here we have used a specific mossy-fibre synaptosome preparation to quantify levels of proteins and measure, using a chemiluminescent glutamate assay, depolarization-induced glutamate release from these synaptosomes after induction of LTP in the dentate gyrus in vivo. We show that 5 h after the induction of LTP, there is an increase in the protein levels of syntaxin 1B and, although to a lesser extent, the synapsins I and II, associated with an increase in depolarization-induced release of glutamate within these terminals. Increases in both the protein levels and glutamate release were not observed when dentate gyrus LTP was blocked by an NMDA receptor antagonist. From these results we propose a molecular mechanism for the propagation of synaptic plasticity through hippocampal circuits.

Cotranscription and intergenic splicing of human galactose-1-phosphate uridylyltransferase and interleukin-11 receptor alpha-chain genes generate a fusion mRNA in normal cells. Implication for the production of multidomain proteins during evolution

In the past 10 years, much attention has been focused on transcription preinitiation complex formation as a target for regulating gene expression, and other targets such as transcription termination complex assemblage have been less intensively investigated. We established the existence of poly(A) site choice and fusion splicing of two adjacent genes, galactose-1-phosphate uridylyltransferase (GALT) and interleukin-11 receptor alpha-chain (IL-11Ralpha), in normal human cells. This 16-kilobase (kb) transcription unit contains two promoters (the first one is constitutive, and the second one, 8 kb downstream, is highly regulated) and two cleavage/polyadenylation signals separated by 12 kb. The promoter from the GALT gene yields two mRNAs, a 1.4-kb mRNA encoding GALT and a 3-kb fusion mRNA when the first poly(A) site is spliced out and the second poly(A) is used. The 3-kb mRNA codes for a fusion protein of unknown function, containing part of the GALT protein and the entire IL-11Ralpha protein. The GALT promoter/IL-11Ralpha poly(A) transcript results from leaky termination and alternative splicing. This feature of RNA polymerase (pol) II transcription, which contrasts with efficient RNA pol I and pol III termination, may be involved, together with chromosome rearrangements, in the generation of fusion proteins with multiple domains and would have major evolutionary implications in terms of natural processes to generate novel proteins with common motifs. Our results, together with accumulation of genomic informations, will stimulate new considerations and experiments in gene expression studies.

Cells of the neuronal lineage play a major role in the generation of amyloid precursor fragments in gelsolin-related amyloidosis

Gelsolin-related amyloidosis or familial amyloidosis, Finnish type (FAF) (OMIM No105120) is a hereditary amyloid disease caused by a mutation in a precursor protein for amyloid (gelsolin) and characterized by corneal dystrophy and polyneuropathy. In vitro expression of the FAF-mutant (Asp187 --> Asn/Tyr) secretory gelsolin in COS cells leads to generation of an aberrant polypeptide presumably representing the precursor for tissue amyloid. Here, we provide evidence that this abnormal processing results from defective initial folding of the secreted FAF gelsolin due to the lack of the Cys188-Cys201 disulfide bond, normally formed next to the FAF mutation site. We compared cells of different tissue origin and discovered a dramatic difference between the amount of cleavage of FAF gelsolin to the amyloid precursor in neuronal and non-neuronal cells. More than half of the mutant gelsolin was cleaved in PC12 and in vitro differentiated human neuronal progenitor cells. In contrast, human fibroblasts and Schwannoma cell cultures showed only a limited capacity to cleave FAF gelsolin, although the cleavage mechanism per se seems to be similar in the various cell types. The present findings of processing and distribution of secreted FAF gelsolin in the neuronal cells emphasize the role of neurons in the tissue pathogenesis of this amyloid polyneuropathy.

Human tyrosine hydroxylase isoforms. Inhibition by excess tetrahydropterin and unusual behavior of isoform 3 after camp-dependent protein kinase phosphorylation

Human tyrosine hydroxylase exists as four isoforms (hTH1-4), generated by alternative splicing of pre-mRNA, with tissue-specific distribution. Unphosphorylated hTH3 and hTH1 were produced in large amounts in Escherichia coli and purified to homogeneity. The phosphorylation sites were determined after labeling with [32P]phosphate in the presence of cAMP-dependent protein kinase (PKA) and calmodulin-dependent protein kinase II (CaM-PKII). Ser40 was phosphorylated by PKA, and both Ser19 and Ser40 were phosphorylated by CaM-PKII. The enzyme kinetics of hTH3 were determined in the presence of various concentrations of the natural co-substrate (6R)-tetrahydrobiopterin and compared with those of recombinant hTH1 (similar to rat TH). We show that, under initial velocity conditions, excess (6R)-tetrahydrobiopterin inhibits hTH3 and hTH1. The TH catalytic constants (kcat) were determined for each of the two isoenzymes: hTH3 is about five times more active than hTH1. Phosphorylation by CaM-PKII did not affect the kinetic parameters of hTH3. The classical activation of TH by PKA phosphorylation, demonstrated for hTH1, was not observed with hTH3. Furthermore, hTH3 escapes activity regulation by phosphorylation and is always more active than phosphorylated hTH1. The properties of the hTH3 enzyme may be relevant to diseases affecting dopaminergic cells.

The cholinergic locus: ChAT and VAChT genes

The gene encoding the vesicular acetylcholine transporter has been localized within the first intron of the gene encoding choline acetyltransferase and is in the same transcriptional orientation. These two genes, whose products are required for the expression of the cholinergic phenotype, could therefore be coregulated. The promoters of both genes have been identified. The mechanisms that account for the regulation of the expression of both genes are now being investigated.

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.

A tetranucleotide polymorphic microsatellite, located in the first intron of the tyrosine hydroxylase gene, acts as a transcription regulatory element in vitro

The polymorphic HUMTH01 microsatellite, located in the first intron of the tyrosine hydroxylase gene is characterized by a tetranucleotide core motif. The 10 repeat allele of this microsatellite exhibits two sequence variants: an imperfect repeat and a perfect repeat. Here we present evidence that this tetrarepeat is endowed with regulatory properties. Constructions were made linking the 10 repetition alleles to the luciferase reporter gene under the control of a thymidine kinase minimal promoter. In transient transfection experiments in HeLa, PC12 and SK-NSH cell lines these repeated sequences increased the basal transcription up to 9-fold. This effect was independent of the sequence orientation, a feature characteristic of an enhancer element. In electrophoretic mobility shift assays these tetrameric repeated sequences form specific complexes with HeLa cell nuclear extracts. Competition experiments with heterologous sequences suggest that proteins of the Fos-Jun family may be involved in the formation of these complexes, although other unidentified transacting factors bind to these sequences. These results thus implicate the HUMTH01 microsatellite in the regulation of tyrosine hydroxylase gene expression. Tetrarepeated sequences of this type may constitute a new class of regulatory elements.

Psychiatric genetics: search for phenotypes

Failure to obtain convincing results in psychiatric genetics can partly be attributed to the fact that progress in molecular biology and genetic epidemiology has not been followed by an equivalent development in phenotypic description. Instead of relying entirely on classical nosological approaches, we argue that identifying more homogeneous forms of diseases through a'candidate symptom approach' among affected subjects and an endophenotype approach that identifies sub-clinical traits among non-affected relatives might yield better results. Examples where these strategies have already been fruitful when applied to complex diseases are presented in this review. Focusing on vulnerability traits might stimulate the redefinition of traditional psychiatric syndromes and help to bridge the gap between clinical and experimental approaches.

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.

CRE and TRE sequences of the rat tyrosine hydroxylase promoter are required for TH basal expression in adult mice but not in the embryo

Tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesis of catecholamine neurotransmitters, is expressed in a restricted number of areas, and subject to numerous regulations during development and in adulthood. Two transcription factor binding sites present in the proximal region of the TH gene, the TPA-responsive element (TRE) and the c-AMP responsive element (CRE), have been shown to play important roles in TH gene regulation in vitro. In order to elucidate in vivo the role of these two sites, we produced transgenic mice bearing a 5.3-kb fragment from the 5' flanking sequence of the TH gene with mutations in either the CRE-or TRE-sites. Using the intact 5.3-kb fragment fused to two different reporter genes (HSV1-tk and lacZ), we show that this promoter fragment is able to specifically direct expression in catecholaminergic tissues both in adult mice and embryos. Interestingly, the CRE- and TRE-mutated transgenes were not expressed in adult mice, contrary to the situation in embryos where they were specifically expressed in catecholaminergic regions. These results demonstrate that the CRE and TRE play an essential role in basal TH expression in adult tissues in vivo. Moreover, they suggest that distinct transcription factors are involved in TH regulation in developing and adult tissues. In support of this, gel mobility shift experiments revealed a complex present only in embryonic tissues. Taken together, these data highlight the diversity of the mechanisms underlying the establishment and maintenance of the catecholaminergic phenotype.

Manic depressive illness and tyrosine hydroxylase gene: linkage heterogeneity and association

Several studies have implicated the tyrosine hydroxylase (TH) locus within the 11p15 region in susceptibility to manic depressive illness (MDI). This possibility was further investigated by both parametric (lod score) and nonparametric (affected-pedigree-member and a case-control study) methods of analysis in 11 French MDI families and in a sample of 200 unrelated subjects. Both types of analyses corroborate the implication of this locus, and positive lod scores were obtained in two families, which most likely reflects genetic heterogeneity. Statistical analyses were also performed including available data from published reports. These analyses, which allowed for genetic heterogeneity, substantiated our findings. The combined maximum lod score for all the families studied was 3.68 at theta = 0.00 (number of families: 36) assuming heterogeneity (alpha = 15%, P = 0.01). Taken together these results converge to suggest that the risk factors for MDI lie in the 11p15 region with TH being the most likely candidate gene.

Association between the tryptophan hydroxylase gene and manic-depressive illness

BACKGROUND

Genes encoding proteins involved in serotonergic metabolism are major candidates in association studies of mood disorders and suicidal behavior. This association study explores whether the tryptophan hydroxylase (TPH) gene, which codes for the rate-limiting enzyme of serotonin biosynthesis, is a susceptibility factor for manic-depressive illness, with or without a history of suicide attempts.

METHODS

The TPH intron 7 A218C polymorphism was determined using a polymerase chain reaction-based method in DNA samples from 152 patients with bipolar disorder and 94 healthy control subjects.

RESULTS

There was a significant association between TPH genotypes and manic-depressive illness. Among patients with bipolar disorder, no association was found between TPH alleles and suicidal behavior.

CONCLUSIONS

This result suggests the involvement of the TPH gene in susceptibility to manic-depressive illness. This preliminary result requires confirmation in further groups of patients and controls.

In vivo adenovirus-mediated gene transfer for Parkinson's disease

Gene therapy is a potentially powerful approach to the treatment of neurological diseases. Neurotransmitter synthesizing enzymes and neurotrophic factors inhibiting neurodegenerative processes provide the basis for current development of gene therapy strategies for Parkinson's disease. Recently, in vivo gene transfer to the brain has been developed using adenovirus vectors. One of the advantages of recombinant adenovirus is that it can transduce both quiescent and actively dividing cells, thereby allowing both direct in vivo gene transfer and ex vivo gene transfer to neural cells. The expression of adenoviral vectors persists for several months with little inflammation, probably because the brain is partially protected from the immune system. Recombinant adenoviruses are currently being improved, particularly by inactivating viral genes controlling the expression of immunodominant viral proteins. Novel therapeutic tools such as vectors for gene therapy have to be evaluated in terms of efficacy and safety for future clinical trials. These vectors still need to be improved to allow long-term and possibly regulatable expression of the transgene.

Detection of two new polymorphic sites in the human interleukin-1 beta gene: lack of association with schizophrenia in a French population

The pathogenesis of schizophrenia might involve abnormal development of the human brain. Interleukin-1 beta is a cytokine implicated in the development of the central nervous system and therefore its gene is a candidate gene in schizophrenia. Polymorphisms within the coding sequence and the 3'UTR of the IL1 beta gene were searched for using PCR-SSCP. Two polymorphisms, 1B-175/1B-173 and 1B-1765/1B-1763 were found in addition to the previously published TaqI site. Furthermore, a mutant was found in codon 106 (exon 5) of the IL1 beta gene located next to the published polymorphism at the TaqI site and abolishing this site. This novel mutation encodes an Asp in place of an Asn and was only observed in one patient in our French population. Association studies were conducted with the polymorphisms 1B-175/1B-173 and TaqI. There was no allelic or genotypic association between either of the two polymorphisms and schizophrenia. In our population, there is no evidence that the IL1 beta gene is involved in schizophrenia.

Adenovirus-mediated transfer of a functional GAD gene into nerve cells: potential for the treatment of neurological diseases

The recent development of efficient virus-mediated gene transfer into nerve cells allows the prospect of new strategies for the treatment of drug-resistant neurological diseases. Some forms of epilepsy may be amenable to gene therapy. Although there is no obvious candidate gene, the consensual GABA hypothesis of epilepsy suggests that the GAD gene may be beneficial. GAD gene expression may be useful in supplying the inhibitory neurotransmitter GABA to particular critical brain territories. We show herein that a nonreplicative recombinant adenovirus carrying the GAD67 gene under the control of Rous sarcoma virus long terminal repeat promoter is able to express the transgene in primary cultures of neurons and glial cells. Expression of the GAD67 gene was assessed by immunoblotting and immunohistochemical analysis. We demonstrated the functionality of the transgene, the expression of which resulted in production of large amounts of GABA in neuronal and glial cell cultures. Substantial production of the enzyme was also detected for several weeks in infected organotypic slices cultured from new-born rat hippocampal tissues. The virally encoded GAD67 was also expressed in vivo in various brain areas involved in various neurological disorders and thus may be of value for the development of gene therapies.

Gene therapy for Parkinson's disease

Gene therapy is a potentially powerful approach to the treatment of neurological diseases. The discovery of neurotrophic factors inhibiting neurodegenerative processes and neurotransmitter-synthesizing enzymes provides the basis for current gene therapy strategies for Parkinson's disease. Genes can be transferred by viral or nonviral vectors. Of the various possible vectors, recombinant retroviruses are the most efficient for genetic modification of cells in vitro that can thereafter be used for transplantation (ex vivo gene therapy approach). Recently, in vivo gene transfer to the brain has been developed using adenovirus vectors. One of the advantages of recombinant adenovirus is that it can transduce both quiescent and actively dividing cells, thereby allowing both direct in vivo gene transfer and ex vivo gene transfer to neural cells. Probably because the brain is partially protected from the immune system, the expression of adenoviral vectors persists for several months with little inflammation. Novel therapeutic tools, such as vectors for gene therapy have to be evaluated in terms of efficacy and safety for future clinical trials. These vectors still need to be improved to allow long-term and possibly regulatable expression of the transgene.

Fine genetic mapping of LCN1/D9S1826 within 9q34

LCN1 gene encodes the tear lipocalin; the lipocalins are a large and growing family of proteins characterized by their ability to bind small hydrophobic molecules. We report here the location of a dinucleotide repeat microsatellite marker (D9S1826) close to LCN1 gene. Using the CEPH reference families, the position of LCN1 is located within the 9q34 genetic map between D9S23 and D9S158.