Dopamine beta-hydroxylase: two polymorphisms in linkage disequilibrium at the structural gene DBH associate with biochemical phenotypic variation.

Levels of the enzyme dopamine beta-hydroxylase (DbetaH) in the plasma and cerebrospinal fluid (CSF) are closely related biochemical phenotypes. Both are under strong genetic control. Linkage and association studies suggest the structural gene encoding DbetaH (locus name, DBH) is a major locus influencing plasma activity of DbetaH. This study examined relationships of DBH genotype determined at two polymorphic sites (a previously described GT repeat, referred to as the DBH STR and a single-base substitution at the 3' end of DBH exon 2, named DBH*444 g/a), to CSF levels of DbetaH protein in European-American schizophrenic patients, and to plasma DbetaH activity in European-American patients with mood or anxiety disorders. We also investigated linkage disequilibrium (LD) between the polymorphisms in the pooled samples from those European-American subjects (n=104). Alleles of DBH*444 g/a were associated with differences in mean values of CSF DbetaH levels. Alleles at both polymorphisms were associated with plasma DbetaH activity. Significant LD was observed between respective alleles with similar apparent influence on biochemical phenotype. Thus, allele A3 of the DBH STR was in positive LD with DBH*444a, and both alleles were associated with lower plasma DbetaH activity. DBH STR allele A4 was in positive LD with DBH*444 g, and both alleles were associated with higher plasma DbetaH activity. The results confirm that DBH is a major quantitative trait locus for plasma DbetaH activity, and provide the first direct evidence that DBH also influences CSF DbetaH levels. Both polymorphisms examined in this study appear to be in LD with one or more functional polymorphisms that mediate the influence of allelic variation at DBH on DbetaH biochemical phenotypic variation

No evidence for significant linkage between bipolar affective disorder and chromosome 18 pericentromeric markers in a large series of multiplex extended pedigrees.

Bipolar affective disorder (BP) is a major neuropsychiatric disorder with high heritability and complex inheritance. Previously reported linkage between BP and DNA markers in the pericentromeric region of chromosome 18, with a parent-of-origin effect (linkage was present in pedigrees with paternal transmission and absent in pedigrees with exclusive maternal inheritance), has been a focus of interest in human genetics. We reexamined the evidence in one of the largest samples reported to date (1,013 genotyped individuals in 53 unilineal multiplex pedigrees), using 10 highly polymorphic markers and a range of parametric and nonparametric analyses. There was no evidence for significant linkage between BP and chromosome 18 pericentromeric markers in the sample as a whole, nor was there evidence for significant parent-of-origin effect (pedigrees with paternal transmission were not differentially linked to the implicated chromosomal region). Two-point LOD scores and single-locus sib-pair results gave some support for suggestive linkage, but this was not substantiated by multilocus analysis, and the results were further tempered by multiple test effects. We conclude that there is no compelling evidence for linkage between BP and chromosome 18 pericentromeric markers in this sample.

Restoration of methylmercury inhibited adenosine triphosphatases during vitamin and monothiol therapy.

The aim of our investigation was to examine the efficacy of monothiols and vitamins in the restoration of ion-dependent ATPases in mice intoxicated with methylmercury chloride (MMC). A daily dose of glutathione (GSH), N-acetyl-DL-homocysteine thiolactone (NAHT), vitamin B complex, or vitamin E, either alone or in combination, resulted in significant recovery of N+, K+, Mg++ ATPases. A significant recovery was noted in some therapeutic groups. As the therapeutic agents used in this study are natural physiological components present in all the animals, they are unlikely to be injurious if applied in appropriate doses. Hence, they can be safely recommended for methylmercury detoxication.

Assignment of the 5HT7 receptor gene (HTR7) to chromosome 10q and exclusion of genetic linkage with Tourette syndrome.

A novel serotonin receptor designated 5HT7 (genetic locus HTR7) was cloned in 1993. This receptor has interesting properties related to ligand affinity and CNS distribution that render HTR7 a very interesting candidate gene for neuropsychiatric disorders. We mapped this gene, first by physical methods and then by genetic linkage. First, we made a tentative assignment to chromosome 10, based on hybridization of an HTR7 probe to a Southern blot of DNA from somatic cell hybrids. We then identified a genetic polymorphism at the HTR7 locus. We identified one extended pedigree where the polymorphism segregated. Using the LIPED computer program for pairwise linkage analysis, we confirmed the assignment of the gene to chromosome 10, specifically 10q21-q24, based on a lod score of 5.37 at 0% recombination between HTR7 and D10S20 (a chromosome 10 reference marker). Finally, we excluded genetic linkage between this locus and Tourette syndrome under a reasonable set of assumptions.

Allelic variation in the D4 dopamine receptor (DRD4) gene does not predict response to clozapine.

OBJECTIVE: To test the hypothesis that interindividual differences in response to clozapine therapy might be attributable to the D4 dopamine receptor (DRD4) alleles they carry. Different alleles of the D4 dopamine receptor, coded by the DRD4 gene, differ in the affinity with which they bind the atypical antipsychotic drug clozapine in vitro. This may have physiologic implications. Clinical response to clozapine therapy varies among patients. The observation that, in vitro, clozapine binds the protein products of different DRD4 alleles with differing affinity characteristics suggested this hypothesis. METHOD: The region of the DRD4 gene that encodes the putative third cytoplasmic loop of the D4 receptor contains a 48-base pair sequence repeated a variable number of times. With use of polymerase chain reaction amplification, we assessed this variable number of tandem repeats polymorphism in a series of schizophrenic and schizoaffective subjects who had been treated with clozapine, and related genotype with treatment response, to test the hypothesis that DRD4 alleles lead to varying response to clozapine. RESULTS: Allelic variation at the DRD4 locus does not predict clinical response to clozapine relative to either fluphenazine hydrochloride or placebo in subjects with treatment-refractory schizophrenia or schizoaffective disorder. CONCLUSIONS: DRD4 alleles do not predict therapeutic response to clozapine in schizophrenic and schizoaffective patients. There are implications from these data for the pathophysiology of schizophrenia and the mechanism of clozapine's therapeutic effect are discussed.

Genetic association between dopamine transporter protein alleles and cocaine-induced paranoia.

Paranoia in the context of cocaine abuse is common and potentially dangerous. Several lines of evidence suggest that this phenomenon may be related to function of the dopamine transporter protein (DAT). DAT is the site of presynaptic reuptake of dopamine, an event that terminates its synaptic activity. The gene coding for dopamine transporter protein (DAT1) contains a variable number of tandem repeats (VNTR) polymorphism in the 3' untranslated region that can be typed by the polymerase chain reaction (PCR) (Vandenbergh et al. 1992). Although this is not a coding region polymorphism, it is close to the coding region and could plausibly be in linkage disequilibrium with a mutation in the gene. Cocaine blocks the dopamine transporter and increases synaptic availability of dopamine. We examined DAT alleles in 58 white and 45 black cocaine users in order to test only two hypotheses: (1) Is there an allelic association between DAT and cocaine dependence? and (2) Is there an allelic association between DAT and cocaine-induced paranoia? We did not demonstrate an allelic association with cocaine dependence. However, within the white sample, DAT genotype was associated with cocaine-induced paranoia (allele frequency for allele 9 = .16 for those without paranoid experiences versus .35 for those with, chi 2 = 3.9 [2 x 2 table], p < .05). There was no significant difference for the same measure in the black sample. Certain DAT genotypes may therefore predispose to paranoia in the context of cocaine use in white populations. We caution that these results require independent replication.

Ontogeny of dopamine D1 and D2 receptor subtypes in rat basal ganglia: a quantitative autoradiographic study.

The ontogeny of D1 and D2 dopamine (DA) receptors in rat basal ganglia was examined by quantitative autoradiography using the iodinated ligands [125I]SCH 23982 and [125I]iodobenzamide [( 125I]IBZM), respectively. Temporal and spatial differences in the development of the receptor subtypes were observed. Scatchard transformation of saturation isotherms conducted at postnatal day 10 (P10) and P60, showed that there was no age-related change in the affinity of [125I]SCH 23982 binding to D1 receptors (Kd = 2.6 nM) but there was a significant increase in the Bmax (771 compared to 2032 fmol/mg protein, P = 0.002). A statistically significant difference in Kd was noted between ages P10 and P60 for [125I]IBZM labelling of D2 receptors (0.62 vs 1.00 nM, respectively, P less than 0.01). A significant increase in the Bmax (211 and 721 fmol/mg protein, P less than 0.01) was also observed. D1 receptors were visible as distinct patches at P1. The highest density was found in the ventrolateral caudate-putamen (CPu). By P5 the patches were found in all subregions of the CPu and nucleus accumbens. Between P7 and P10 the binding became distinctly less patchy due to a marked increase in the density of D1 receptors in non-patch (matrix) regions. Adult levels of receptor were seen by P30. The concentration of DA (measured by HPLC) and binding of [3H]mazindol to DA uptake sites in whole striatum showed similar and nonlinear increases with age. The age-related change in the topography of binding sites for [3H]mazindol was similar to that of D1 receptors at the same ages. Both D2 receptors and [3H]hemicholinium-3 (HC-3) binding to high affinity transport sites for choline developed initially in the dorso-lateral CPu. Their topography was largely overlapping but distinct from that of the D1 receptor. D2 receptors were not consistently observed until P3 in the CPu, and zones of enriched binding were aligned with zones of low density for D1 receptors. The density of D2 receptors reached adult levels by P30. The differential development of the DA receptors was also evident in the substantia nigra (SN) and globus pallidus (GP). D1 receptors were found in SN prior to the appearance of D2 receptors and throughout development the density was greater in pars reticulata than in pars compacta, whereas the density of D2 receptors was higher in the pars compacta. At all ages the density of D1 receptors was greater than the density of D2 receptors in the GP and reached adult levels before reaching it in the CPu or SN.(ABSTRACT TRUNCATED AT 400 WORDS)

Acute and short term effects of ethanol on membrane enzymes in rat brain.

Changes in the biophysical and biochemical character of membranes brought about by ethanol have been emphasized in the underlying mechanism of alcohol toxicity. Membrane enzymes such as Na+, K+ activated ATPase, 5'-nucleotidase, and gamma-glutamyl transpeptidase were studied in cerebral cortex, cerebellum, and brain stem of rats subjected to acute and short term ethanol toxicity. Acute ethanol toxicity was induced by intraperitoneal injection of 1 ml of 7M ethanol per 100 g body weight of rat and the animals were sacrificed half an hour after the administration. Short term ethanol toxicity was induced by intraperitoneal injections of 0.5 ml (7 M ethanol) per 100 g weight of the rat for 7 days and the animals were sacrificed half an hour after the last injection. In acute ethanol toxicity the activity of Na+, K+-activated ATPase was found to decrease significantly in cerebral cortex and brain stem, while in short term alcohol toxicity, the activity was found to increase in cerebral cortex and cerebellum. The activity of gamma-glutamyl transpeptidase was found to increase in all the three regions in acute and short term ethanol toxicity. No change in the activity of 5'-nucleotidase was observed in any of the regions either in acute or in chronic ethanol toxicity. While a significant increase in the activity of adenosine deaminase was found in cerebral cortex, cerebellum, and brain stem in acute ethanol toxicity, the same was found to decrease significantly in cerebral cortex and a persistent increase in brain stem in short term ethanol toxicity. The above changes in the activities of the enzyme were discussed with reference to the well known changes in the membrane structure and consequent alteration in brain function.