Twelve-Nucleotide Repeat Polymorphism of D4 Dopamine Receptor Gene in Chinese Familial Schizophrenic Patients

Background: Disturbances in dopaminergic transmission have been implicated in the etiology of schizophrenia. Catalano et al reported an association between delusional disorder and the number of a 12-nucleotide (bp) repeat sequence in the first exon of dopamine D4 receptor gene (DRD4), which indicated a possible role of this polymorphism in the pathogenesis of psychotic disorders. Methods: DNA of 42 Chinese controls, 50 sporadic schizophrenic patients, and 30 familial schizophrenic probands were collected. Genotype of the 12-bp repeat polymorphism of DRD4 was determined with polymerase chain reaction and agarose gel electrophoresis. Genotypic and allelic frequencies were compared among the three groups using the chi-square test. Results: Forty-three (86%) sporadic schizophrenic patients, 25 (83.3%) familial schizophrenic probands, and 35 (83.3%) controls were A1 (two 12-bp repeat) homozygotes. One (2.0%) sporadic schizophrenic and 1 familial schizophrenic patient were A2 (one 12-bp repeat) homozygotes. There was no significant difference in allelic and genotypic distributions among the three groups. Conclusions: The present data do not support an association between schizophrenia and any specific allele of the 12-bp repeat polymorphism of DRD4. Significance of familial/sporadic division of schizophrenia cannot be supported regarding this repeat polymorphism.