Polymorphisms of dopamine D2-like (D2, D3, and D4) receptors in schizophrenia.

The result of most association studies and linkage analyses have suggested a negative association between schizophrenia and D2-like (D2, D3, and D4) receptor polymorphisms. Although the polymorphisms of the D2-like receptor in themselves may not account for the etiology of schizophrenia, they can contribute to the severity of the symptoms. Thus, we studied the associations between the polymorphisms and their combinations, and the vulnerability of schizophrenics. Fragments of the D2-like receptor genes were amplified by means of the polymerase chain reaction, and the polymorphisms were identified by the restriction fragment length polymorphism and single-stranded conformation polymorphism methods. There were no statistically significant differences in the polymorphisms and their combinations between schizophrenics and controls. Schizophrenics with D4E1(A1/A2), which contains 2 and 1 tandem repeats of a 12-base-pair sequence in exon 1, had a lower total positive symptom score before medication than schizophrenics with D4E1(A1/A1). There was no association between the polymorphisms and negative symptoms.