Ethnic heterogeneity in allele variation in the DRD4 gene in schizophrenia

The goal of the present study was to use a meta-analysis on previous studies plus our own unpublished data to confirm and extend findings which indicate that the variation in the dopamine D4 receptor (DRD4) gene is best represented by a mixture of two different ethnic groups. The genotype distribution was divided into either a long or short form using a mixture analysis of normal controls of different ethnic origins under the assumption that there is a single major gene. The meta-analysis was based on the data from 19 independent samples, 18 association studies, and from our own unpublished data, including a total of 1431 schizophrenic patients (sporadic cases 1309, familial cases 122) and 1439 controls. No significant genotype differences were noted between patients and controls for the whole sample. However, reorganization of the studies into different groups by the geographical origin of samples revealed significant ethnic heterogeneity. In addition, there was a significant association between the long form of DRD4 gene and schizophrenia in Caucasians, especially those with familial schizophrenia.