Association Analysis Between Interleukin 1 Beta Locus-511 Gene Polymorphism and Bipolar I Disorder: A Case-control Study in an Iranian Population

Background: Bipolar I disorder (BPI) is one of the significant disabling psychiatric disorders resulting in severe deficits in the social and personal function of suffering patients. Among its etiologies, immunologic and genetic disturbances are two important areas of interest. Objectives: This study aimed to assess the potential role of interleukin1β (IL1β)511 polymorphism in BPI pathogenesis based on a previous pilot study. Methods: After diagnostic interviews held by two psychiatrists using structured clinical interview for DSM disorder (SCID), 102 bipolardiagnosed hospitalized patients in IbneSina Hospital, Mashhad, Iran, were selected and compared with 102 healthy individuals of the control group. The DNA was extracted from the blood samples of each group. Genetic locus 511 of IL1β was defined by its specific primers. Polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) were also carried out. The two groups’ results were compared by SPSS20 using the chisquare test. Results: There were no significant differences in the genotypic frequency of IL1β locus 511 (P = 1) and C/T allelic frequency (P = 0.42) between bipolar and control groups. There was also no significant difference in the allelic frequency between psychotic and nonpsychotic subgroups (P = 0.218) and suicidal and nonsuicidal subgroups of bipolar patients (P = 0.829). The genotypic distribution of 511 IL1β polymorphisms in the control group was in the HardyWeinberg equilibrium. Conclusions: In contrast with a previous pilot study, this study found no relationship between BPI and genotypic and C/T allelic frequencies of 511 IL1β polymorphism. There were also no associations between the allelic frequency and two subgroups of psychotic/nonpsychotic and suicidal/nonsuicidal of bipolar patients.