Plasma dopamine β-hydroxylase activity in a North Swedish isolate with a high frequency of schizophrenia

Plasma dopamine β-hydroxylase (DBH) activity was determined in 115 members of a North Swedish geographical isolate with a high frequency of schizophrenia, of which 30 persons had schizophrenia, and was compared with a Middle Swedish population of 185 apparently healthy persons. There was no significant difference between the schizophrenic group and their healthy relatives or between the North and Middle Swedish populations. The number of persons with very low plasma DBH activity in the North Swedish population appeared to be less than those in the control population.     

Analysis of the polymorphic (GT)(n) repeat at the dopamine beta-hydroxylase gene in Spanish patients affected by schizophrenia

The presence of a polymorphic (GT)(n) repeat, a microsatellite repeat, at the human dopamine beta-hydroxylase (DBH) gene had been previously investigated in healthy people and in schizophrenic patients. The different DBH genotypes had been found to be associated to different DBH biochemical function, but no differences were found in the allelic and genotype frequencies between schizophrenic and control groups. To further clarify the potential involvement of the variation at the DBH gene in schizophrenia we have studied the DBH (GT)(n) repeat in a sample of 47 Spanish schizophrenic patients, in their healthy relatives (n = 72), and in a control population (n = 74). We have been able to identify five different variants of the DBH gene (A1, A2, A3, A4, A5) in the different groups. Subsequent statistical analysis revealed that the genotypes as well as the allele frequencies did not differ significantly among schizophrenic patients and the control population. Interestingly, the allelic variant A2 and the genotype A4/A2 were significantly more frequent in schizophrenic patients as compared with their healthy relatives. However, the association of the A2 allele with schizophrenia was not supported by the haplotype relative risk analysis of transmitted versus nontransmitted alleles. Therefore, although it will be important to extend the present analysis in a larger sample of schizophrenic patients and controls, our results suggest that the (GT)(n) does not seem to play a major role in the genetics of schizophrenia at least in this group of Spanish schizophrenic patients. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:88-92, 2000.     

Effect of SOX10 gene polymorphism on early onset schizophrenia in Chinese Han population

Schizophrenia is one of highly heritable psychiatric disorders. Patients with early onset schizophrenia tend to have a greater genetic loading and may be an attractive subpopulation for genetics studies. A single nucleotide polymorphism (SNP) rs139887 in sex-determining region Y-box 10 (SOX10), a candidate gene for schizophrenia, was suggested to be associated with schizophrenia although inconsistent results had been reported. The aim of this study was to evaluate the association between SOX10 rs139887 polymorphism and schizophrenia using an early onset sample in the Chinese Han population. A total of 321 schizophrenic patients with onset before age 18 and 400 healthy controls were recruited for association study. In addition, two populations involved in three studies were selected for meta-analysis to determine the effect of rs139887 on schizophrenia. Our association study results showed that the allele and genotype frequencies were significantly different between schizophrenic patients and controls (P=0.013 and P=0.034, respectively). Interestingly, a significant association in allele and genotype frequencies were found in male patients (P=0.017 and P=0.045, respectively), but not female patients. Moreover, the C/C genotype had a significant association with an earlier age of onset in male schizophrenic patients (Kaplan-Meier log-rank test P=0.029), but not in female patients (Kaplan-Meier log-rank test P=0.876). The meta-analysis result showed the same C allele was significantly associated with schizophrenia (P=0.007). In conclusion, the SOX10 rs139887 polymorphism was related to the development of schizophrenia in a gender-specific manner, and may be a significant genetic marker for managing subgroups and etiological clues in schizophrenia.     

Association between schizophrenia and DRD3 or HTR2 receptor gene variants

Schizophrenia is a severe and common psychiatric disorder afflicting 1% of the world population. A role of many neurotransmitter receptors in schizophrenia was suggested by an association with several polymorphisms located in their coding regions. In this study we examined the contribution of the T-102C and A-206G transitions in the 5-HTR2a and DRD3 receptor genes respectively to genetic susceptibility and phenotypic expression of schizophrenia disorder within the Greek population. We determined by PCR and RFLP analysis the genotype for the above polymorphisms in 114 schizophrenic hospitalized individuals and 192 control samples. In contrast to previous reports from large European multicentre studies, which indicate significant correlation between schizophrenia and C-102 allele of the T-102C polymorphism, in this study we observed a statistically significant overall association between the disorder and allele T-102 (P<0.0001, odds ratio (OR)=2.11, 95% CI=1.48-3.02). We also found a highly significant excess of the T-102/C-102 and C-102/C-102 genotypes in the normal group (P<0.001). Comparison of the patients with the controls for the DRD3 polymorphism (A-206G transition) showed marginally nonsignificant differences in the genotypic (P=0.054) and no significance in the allelic (P=0.163) frequencies. However, the A-206/A-206 genotype seems to positively contribute to the disorder appearance, when compared to A-206/G-206 as genotype base line risk (P=0.016, OR=1.88, 95% CI=1.09-3.26). In conclusion, from genetic association analysis of this schizophrenic population, a significant association is clearly determined between the HTR2 genetic polymorphism and the presence of schizophrenic disorder, manifested as increased risk of schizophrenia for carriers of the T-102 allele.     

Thermal stability and the biochemical genetics of erythrocyte catechol-O-methyltransferase and plasma dopamine-β-hydroxylase

The levels of activity of human erythrocyte (RBC) catechol-O-methyl-transferase (COMT) and human plasma dopamine-β-hydroxylase (DBH) are inherited in a monogenic fashion. The COMT in erythrocytes of subjects homozygous for the allele for low basal enzyme activity, COMT ^L, is more thermolabile than that in the erythrocytes of subjects with genetically high basal enzyme activity. This observation suggests that the locus COMT may represent the structural gene for COMT in man. Wide individual variations in the thermal stability of human plasma DBH also occur. There is a significant familial aggregation of the trait of thermolabile plasma DBH. Although subjects with thermolabile plasma DBH have average basal plasma DBH activity only about 55% of that of subjects with thermostable enzyme, the trait of thermolability does not cosegregate with DBHL ^L, the allele for very low basal plasma DBH activity. Studies of thermal stability may help to increase our understanding of the biochemical basis of the genetic regulation of catecholamine enzymes in man.     

Haplotype-controlled analysis of the association of a non-synonymous single nucleotide polymorphism at DBH (+ 1603C --> T) with plasma dopamine beta-hydroxylase activity.

The DBH locus controls plasma dopamine beta-hydroxylase activity (pDbetaH). A 5'-upstream single nucleotide polymorphism (SNP) at DBH (-1021C --> T) explains approximately 45% of the variance in pDbetaH, and a non-synonymous SNP in exon 11 (+ 1603C --> T) an additional 2%. However, that regression result underestimates the effect of + 1603C --> T because of its low minor allele frequency. We estimated the biological effect of + 1603C --> T on pDbetaH by comparing subjects of identical -1021CgammaT genotype, in a diagnostically heterogeneous group of subjects of European origin (N = 367). + 1603C --> T genotype associated with pDbetaH within groups of identical genotype at -1021 C --> T, accounting for 5%-16% of the variance. There was no significant linkage disequilibrium between -1021C --> T and + 1603C --> T (D = 0.0058, D' = 0.4774, d(2) = 0.0011, P > 0.05), confirming the validity of assessing the two polymorphisms independently. These results suggest that altered homospecific activity of the enzyme can contribute to variation in pDbetaH. This conclusion informs how associations between DBH and psychiatric disorders should be approached. (c) 2005 Wiley-Liss, Inc.     

Case-control association study of the 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) gene and schizophrenia in the Han Chinese population

Converging evidence from imaging, microarray, genetic, and other studies suggests that abnormalities in myelin may play a role in schizophrenia. The expression of 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP), which is used as a myelin marker, has been reported to be reduced in the schizophrenic brain. A synonymous genetic variation in the CNP gene, rs2070106, has recently been shown to be associated with schizophrenia in Caucasians. The present study investigates whether this finding can be replicated in the Han Chinese population. We performed an association analysis of four ht-SNPs in the CNP gene in a Chinese sample consisting of 426 schizophrenic patients and 439 healthy controls. We did not find any significant differences in any genotypic, allelic or haplotypic distributions between patients and controls. Therefore, this study did not find an association between genetic variations in the CNP gene and schizophrenia in the Han Chinese population.     

Genetic variation in DTNBP1 influences general cognitive ability

Human intelligence is a trait that is known to be significantly influenced by genetic factors, and recent linkage data provide positional evidence to suggest that a region on chromosome 6p, previously associated with schizophrenia, may be linked to variation in intelligence. The gene for dysbindin-1 (DTNBP1) is located at 6p and has also been implicated in schizophrenia, a neuropsychiatric disorder characterized by cognitive dysfunction. We report an association between DTNBP1 genotype and general cognitive ability (g) in two independent cohorts, including 213 patients with schizophrenia or schizo-affective disorder and 126 healthy volunteers. These data suggest that DTNBP1 genetic variation influences human intelligence.     

Lack of significant association between -1021C-->T polymorphism in the dopamine beta hydroxylase gene and attention deficit hyperactivity disorder

Recent trends in medications for attention deficit hyperactivity disorder (ADHD) suggest that norepinephrine (NE) deficiency may contribute to the disease etiology. Dopamine beta hydroxylase (DBH) is the key enzyme which converts dopamine to NE and since DBH gene is considered a major quantitative trait locus for plasma DBH activity, genetic polymorphism may lead to altered NE neurotransmission. Several polymorphisms including a 5' flanking -1021C-->T polymorphism, was reported to be associated with changed DBH activity and an association between -1021C-->T polymorphism with ADHD was observed in Han Chinese children. We have carried out family-based studies with three polymorphisms in the DBH gene, -1021C-->T polymorphism, exon 2*444g/a and intron 5 TaqI RFLP, to explore their association with Indian ADHD cases. Allele and genotype frequency of these polymorphisms in ADHD cases were compared with that of their parents and a control group. Haplotypes obtained were analyzed for linkage disequilibrium (LD). Haplotype-based haplotype relative risk analysis and transmission disequilibrium test showed lack of significant association between transmission of the polymorphisms and ADHD. A haplotype comprising of allele 1 of all polymorphisms showed a slight positive trend towards transmission from parents to ADHD probands. Strong LD was observed between *444g/a and TaqI RFLP in all the groups. However, low D' values and corresponding log of odds scores in the control group as compared to the ADHD families indicated that, the incidence of the two polymorphisms being transmitted together could be higher in ADHD families.     

Positive association of the human frizzled 3 (FZD3) gene haplotype with schizophrenia in Chinese Han population.

Frizzled 3 (FZD3) gene is located on chromosome 8p21, a region that has been implicated in schizophrenia in genetic linkage studies. The FZD3 is a transmembrane receptor required for Wnt signal transduction cascades that have been thought to be involved in producing the cytoarchitectural defects observed in schizophrenia. Previous work has showed a strong association between FZD3 locus and schizophrenia in family-based study. To confirm this issue further, we investigated a genetic association between four single nucleotide polymorphisms (SNPs) located in the FZD3 gene and schizophrenia by case-control study using polymerase chain reaction (PCR)-based restriction fragment length polymorphism (RFLP) in the Chinese Han population. Our studies showed the SNPs rs2323019 and rs880481 have significant differences in both genotype and allele frequencies between control subjects and schizophrenic patients (rs2323019: Allele A > G, chi2 = 6.7277, df = 1, P = 0.0095; Genotype, chi2 = 10.6583, df = 2, P = 0.0049; rs880481: Allele A > G, chi2 = 10.3945, df = 1, P = 0.0013; Genotype, chi2 = 16.8049, df = 2, P = 0.0002). In addition, we constructed three-locus haplotypes to test their association with schizophrenia. The globe chi-squared test for haplotype analysis showed a significant association (chi2 = 66.38, df = 7, P < 0.000001). These results suggested that the FZD3 gene might be involved in the predisposition to schizophrenia.     

A family study of HLA antigens and other genetic markers in schizophrenia

HLA antigens and 19 other genetic marker systems were studied in 12 families containing 2 or more members diagnosed as schizophrenic. In contrast with previous reports we could exclude linkage between the disorder and HLA, and we found no evidence of linkage with Gm or Gc. The disagreement between our results and those of a previous study, which suggested linkage between HLA and schizophrenia, could not be explained on the basis of genetic heterogeneity within the disorder. The problems of performing a linkage study in the face of diagnostic uncertainty and an unknown mode of inheritance of the main trait are discussed, and the measures taken in attempts to overcome these difficulties are described. Despite present drawbacks, genetic marker studies hold future promise as a means of detecting major gene effects in schizophrenia and other familial psychiatric disorders.     

Physiogenomic Analysis of Localized fMRI Brain Activity in Schizophrenia

The search for genetic factors associated with disease is complicated by the complexity of the biological pathways linking genotype and phenotype. This analytical complexity is particularly concerning in diseases historically lacking reliable diagnostic biological markers, such as schizophrenia and other mental disorders. We investigate the use of functional magnetic resonance imaging (fMRI) as an intermediate phenotype (endophenotype) to identify physiogenomic associations to schizophrenia. We screened 99 subjects, 30 subjects diagnosed with schizophrenia, 13 unaffected relatives of schizophrenia patients, and 56 unrelated controls, for gene polymorphisms associated with fMRI activation patterns at two locations in temporal and frontal lobes previously implied in schizophrenia. A total of 22 single nucleotide polymorphisms (SNPs) in 15 genes from the dopamine and serotonin neurotransmission pathways were genotyped in all subjects. We identified three SNPs in genes that are significantly associated with fMRI activity. SNPs of the dopamine beta-hydroxylase (DBH) gene and of the dopamine receptor D4 (DRD4) were associated with activity in the temporal and frontal lobes, respectively. One SNP of serotonin-3A receptor (HTR3A) was associated with temporal lobe activity. The results of this study support the physiogenomic analysis of neuroimaging data to discover associations between genotype and disease-related phenotypes.     

PRODH mutations and hyperprolinemia in a subset of schizophrenic patients

The increased prevalence of schizophrenia among patients with the 22q11 interstitial deletion associated with DiGeorge syndrome has suggested the existence of a susceptibility gene for schizophrenia within the DiGeorge syndrome chromosomal region (DGCR) on 22q11. Screening for genomic rearrangements of 23 genes within or at the boundaries of the DGCR in 63 unrelated schizophrenic patients and 68 unaffected controls, using quantitative multiplex PCR of short fluorescent fragments (QMPSF), led us to identify, in a family including two schizophrenic subjects, a heterozygous deletion of the entire PRODH gene encoding proline dehydrogenase. This deletion was associated with hyperprolinemia in the schizophrenic patients. In addition, two heterozygous PRODH missense mutations (L441P and L289M), detected in 3 of 63 schizophrenic patients but in none among 68 controls, were also associated with increased plasma proline levels. Segregation analysis within the two families harboring respectively the PRODH deletion and the L441P mutation showed that the presence of a second PRODH nucleotide variation resulted in higher levels of prolinemia. In two unrelated patients suffering from severe type I hyperprolinemia with neurological manifestations, we identified a homozygous L441P PRODH mutation, associated with a heterozygous R453C substitution in one patient. These observations demonstrate that type I hyperprolinemia is present in a subset of schizophrenic patients, and suggest that the genetic determinism of type I hyperprolinemia is complex, the severity of hyperprolinemia depending on the nature and number of hits affecting the PRODH locus.     

Alleles at the dopamine D4 receptor locus do not contribute to the genetic susceptibility to schizophrenia in a large Swedish kindred

The discovery of a functional polymrphism within the dopamine D₄ receptor gene (DRD4) has not only strengthened the hypotheses implicating DRD4 in the etiology of neuropyschiatic disorders, but also provided a genetic marker for testing these hypotheses. The possibility of the dopamine D₄ receptor as a candidate gene for schizophrenia was investigated in a large Swedish kindred segregating for schizophrenia. Linkage to schizophrenia was tested by linkage analyses of 6 polymorphic markers (at 4 loci) in chromosome 11p15.5 including the dopamine D₄ receptor (DRD4) and the tyrosine hydroxylase (TH) loci. Schizophrenia was excluded from close linkage to the DRD4 locus using two of the polymorphisms located within the dopamine D₄ receptor gene. The first DRD4 polymorphism consists of variation in the number of a 48 bp imperfect direct repeat in the third exon; the second consists of a variable number of repeated G nucleotides in the first intron. In addition, some of the individuals homozygous for four or seven copies of 48 bp repeat alleles were tested for previously reported sequence variation among repeats. No single haplotype of the DRD4 alleles or haplotype of other markers in chromosome 11p15.5 was found to be common to the schizophrenic individuals in this family. Therefore, we find no evidence for linkage of the D₄ receptor, or this region of 11p15.5, with genetic susceptibility to schizophrenia in this kindred. © 1993 Wiley-Liss, Inc.     

Association between FOXP2 polymorphisms and schizophrenia with auditory hallucinations

OBJECTIVE: A mutation in the FOXP2 gene has been the first genetic association with a language disorder. Language disorder is considered as a core symptom of schizophrenia. Therefore, the FOXP2 gene could be considered a good candidate gene for the vulnerability to schizophrenia. METHODS: A set of single nucleotide polymorphisms mainly located in the 5' regulatory region of the FOXP2 gene was analysed in a sample of 186 DSM-IV schizophrenic patients with auditory hallucinations and in 160 healthy controls. RESULTS: Statistically significant differences in the genotype (P=0.007) and allele frequencies (P=0.0027) between schizophrenic patients with auditory hallucinations and controls were found in the single nucleotide polymorphism rs2396753. These P values changed to 0.07 and 0.0273, respectively, after Bonferroni sequential correction. The haplotype rs7803667T/rs10447760C/rs923875A/rs1358278A/rs2396753A (TCAAA) also showed a significant difference confirmed with a permutation test (P=0.009). CONCLUSIONS: These results suggested that the FOXP2 gene may confer vulnerability to schizophrenic patients with auditory hallucinations.     

Family-based association study of schizophrenia with 444 markers and analysis of a new susceptibility locus mapped to 11q13.3.

Family-based linkage disequilibrium (LD) mapping has been suggested as a powerful and practical alternative to linkage analysis. We have performed a genome-wide LD survey of susceptibility loci for schizophrenia in a Japanese population. We first typed 119 schizophrenic pedigrees (357 individuals) using 444 microsatellite markers, and analyzed the data using the pedigree disequilibrium test. This analysis revealed 14 markers demonstrating significant transmission distortion. To corroborate these findings, the statistical methods were changed to the extended transmission disequilibrium test (ETDT), using 80 independent complete trios (schizophrenic proband and both parents), with 68 derived from initial pedigrees and 12 newly recruited trios. ETDT supported two markers for continued association, D11S987 on 11q13.3 (P = 0.00009) and D16S423 on 16p13.3 (P = 0.002). We scrutinized the most significant genomic locus on 11q11-13 by adding 26 new markers for analysis. Results of three-marker haplotype analysis in the region showed evidence of association with schizophrenia (most significant haplotype P = 0.0005, global P = 0.022). Although the present study may have missed other potential genomic intervals because of the sparse mapping density, we hope that it has identified promising anchor points for further studies to identify risk-conferring genes for schizophrenia in the Japanese population. In addition, we provide useful information on genomic LD structures in Japanese populations, which can be used for LD mapping of complex diseases.     

Mutation analysis of synapsin III gene in schizophrenia

Synapsin III is a new synapsin family gene with the putative function of synaptogenesis regulation and neurotransmitter release in the brain. The gene was mapped to 22q12-q13, a schizophrenia susceptible region gene as suggested by several linkage studies. Hence, the synapsin III gene is considered a candidate gene of schizophrenia. We systematically sequenced the protein coding and 5'-promoter regions of the synapsin III gene to look for mutations in 62 Han Chinese schizophrenic patients from Taiwan with positive family history. Further case-control association study was performed among 163 patients and 151 controls using the genetic polymorphic markers identified from these 62 patients. Three single nucleotide polymorphisms (SNPs) were identified: g.-631C > G and g.-196G>A at 5'-promoter region, and g.69G>A at exon 1. Besides, no other mutations were identified in these patients. The g.69G>A polymorphism does not alter the amino acid threonine at codon 23 (ACG>ACA). Further case-control association studies also did not find significant differences of genotype or allele frequency distributions of these three polymorphisms between 163 patients and 151 non-psychotic comparison individuals. Hence, our data are not in favor of a large effect of synapsin III gene in the pathogenesis of schizophrenia.