A study of enzymes involved in catecholamine metabolism in parents of patients with schizophrenia

Gene-sex interactions in schizophrenia: focus on dopamine neurotransmission

Schizophrenia is a severe mental disorder, with a highly complex and heterogenous clinical presentation. Our current perspectives posit that the pathogenic mechanisms of this illness lie in complex arrays of gene × environment interactions. Furthermore, several findings indicate that males have a higher susceptibility for schizophrenia, with earlier age of onset and overall poorer clinical prognosis. Based on these premises, several authors have recently begun exploring the possibility that the greater schizophrenia vulnerability in males may reflect specific gene × sex (G×S) interactions. Our knowledge on such G×S interactions in schizophrenia is still rudimentary; nevertheless, the bulk of preclinical evidence suggests that the molecular mechanisms for such interactions are likely contributed by the neurobiological effects of sex steroids on dopamine (DA) neurotransmission. Accordingly, several recent studies suggest a gender-specific association of certain DAergic genes with schizophrenia. These G×S interactions have been particularly documented for catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO), the main enzymes catalyzing DA metabolism. In the present review, we will outline the current evidence on the interactions of DA-related genes and sex-related factors, and discuss the potential molecular substrates that may mediate their cooperative actions in schizophrenia pathogenesis.

Tyrosine hydroxylase, interleukin-1beta and tumor necrosis factor-alpha are overexpressed in peripheral blood mononuclear cells from schizophrenia patients as determined by semi-quantitative analysis

The aim of this study is to profile the peripheral biomarkers (tyrosine hydroxylase, TH; interleukin-1beta, IL-1beta; and tumor necrosis factor-alpha, TNF-alpha) for schizophrenia and explore their relations with clinical symptoms. Thirty-nine patients with schizophrenia were evaluated using the Positive and Negative Syndrome Scale (PANSS), and 25 siblings and 30 normal healthy subjects were used as controls. The mRNA expression levels of TH, IL-1beta and TNF-alpha in peripheral blood mononuclear cells, as determined with semi-quantitative reverse transcription-polymerase chain reaction, were all significantly increased in both patients (3-fold) and siblings (2-fold) as compared with normal control. Both IL-1beta and TNF-alpha were significantly correlated with scores on the general psychopathology subscale of the PANSS. A significant positive correlation between IL-1beta and TH expression was found in both sibling and normal controls, but not in patients, while a positive correlation between IL-1beta and TNF-alpha was significant in all the groups. These results suggest that TH, IL-1beta and TNF-alpha are overexpressed in the peripheral blood mononuclear cells of schizophrenia patients, perhaps due to the hereditary factors. IL-1beta and TNF-alpha may influence the symptoms of schizophrenia in the cognition dysfunction and anxiety/depression domains of the PANSS.

Variation in catechol-o-methyltransferase val158 met genotype associated with schizotypy but not cognition: a population study in 543 young men

BACKGROUND

Increased catechol-O-methyltransferase activity associated with variation in catechol-O-methyltransferase valine158 methionine genotypes may result in reduced dopamine neurotransmission in the prefrontal cortex and thus contribute to the poor performance of frontally mediated cognitive tasks and the occurrence of associated negative symptoms observed in patients with schizophrenia; however, reported associations between catechol-O-methyltransferase valine158 methionine genotypes and measures of cognition have not been consistent.

METHODS

Catechol-O-methyltransferase genotyping, measures of schizotypy, cognitive measures of memory and attention, as well as the antisaccade eye movement task, a measure sensitive to prefrontal cortical function, were obtained in a sample of 543 young men representative for that age group (mean age 21 years).

RESULTS

None of the cognitive measures was associated with catechol-O-methyltransferase valine158 methionine genotypes; however, there was an effect of high-activity allele loading on schizotypy, in particular the negative and disorganization dimensions.

CONCLUSIONS

Previously reported inconsistencies in the relationship between catechol-O-methyltransferase valine158 methionine genotypes and cognition were not resolved; however, catechol-O-methyltransferase genotype may affect expression of negative schizotypy by direct or indirect effects on central dopamine neurotransmitter signaling.

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.