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

Bipolar I disorder (BP-I) 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.

This study aimed to assess the potential role of interleukin-1β (IL-1β)-511 polymorphism in BP-I pathogenesis based on a previous pilot study.

After diagnostic interviews held by two psychiatrists using structured clinical interview for DSM disorder (SCID), 102 bipolar-diagnosed hospitalized patients in Ibn-e-Sina 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 IL-1β 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 SPSS-20 using the chi-square test.

There were no significant differences in the genotypic frequency of IL-1β 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 non-suicidal subgroups of bipolar patients (P = 0.829). The genotypic distribution of -511 IL-1β polymorphisms in the control group was in the Hardy-Weinberg equilibrium.

In contrast with a previous pilot study, this study found no relationship between BP-I and genotypic and C/T allelic frequencies of -511 IL-1β polymorphism. There were also no associations between the allelic frequency and two subgroups of psychotic/non-psychotic and suicidal/non-suicidal of bipolar patients.