Tyrosine hydroxylase polymorphism and phenotypic heterogeneity in bipolar affective disorder: a multicenter association study.

Tyrosine hydroxylase (TH), the rate-limiting enzyme in the metabolism of catecholamines, is considered a candidate gene in bipolar affective disorder (BPAD) and has been the subject of numerous linkage and association studies. Taken together, most results do not support a major gene effect for the TH gene in BPAD. Genetic and phenotypic heterogeneity may partially explain the difficulty of confirming the exact role of this gene using both association and linkage methods. Four hundred one BPAD patients and 401 unrelated matched controls were recruited within a European collaborative project (BIOMED1 project in the area of brain research, European Community grant number CT 92-1217, project leader: J. Mendlewicz) involving 14 centers for a case-control association study with a tetranucleotide polymorphism in the TH gene. Patients and controls were carefully matched for geographical origin. Phenotypic heterogeneity was considered and subgroup analyses were performed with relevant variables: age at onset, family history, and diagnostic stability. No association was observed in the total sample or for subgroups according to age at onset (n = 172), family history alone (n = 159), or high degree of diagnostic stability and a positive family history (n = 131). The results of this association study do not confirm the possible implication of TH polymorphism in the susceptibility to BPAD.

European Collaborative Project on Affective Disorders: interactions between genetic and psychosocial vulnerability factors.

Despite strong evidence provided by genetic epidemiology of genetic involvement in the aetiology of bipolar and unipolar affective disorders, the exact nature of the predisposing gene(s) is still being investigated through linkage and association studies. The interaction of susceptibility genes and environmental factors in these diseases is also of fundamental importance and requires proper investigation. Interesting theories have recently been proposed examining the possible role of various chromosomal regions, candidate genes and mutations in affective disorders. Reliable multicentre-based methodology is currently being employed to examine these theories, with attention given to statistical analysis and the statistical power of the sample. The present article describes the European Collaborative Project on Affective Disorders (ECPAD) 'Interactions between genetic and psychosocial vulnerability factors', involving 15 European centres. A description is given of the association and family samples collected for the project and also the methodology used to analyse interactions in the gene-psychosocial environment. This material provides a powerful tool in the search for susceptibility genes in affective disorders and takes into account non-genetic aetiological factors.