Seven loci associated with schizophrenia and bipolar I disorder in selected southern African population groups

Abstract

Two major psychiatric disorders, schizophrenia and bipolar I disorder, are regarded as distinct disorder entities; however, they share intricate connections through characteristic overlap and underlying genetic aetiology, challenging the traditional dichotomy. This convergence emerged as an essential area of investigation in understanding the genetic determinants of schizophrenia and bipolar I disorder. Moreover, psychiatric genetic research has revealed demographic disparities, with South African population groups notably underrepresented. Therefore, this preliminary targeted candidate gene association study of 20 single nucleotide polymorphisms implicated in schizophrenia and bipolar I disorder aimed to investigate association and overlap. Candidate loci for schizophrenia and bipolar I disorder were selected through an exploratory Illumina® Infinium PsychArray-24 analysis combined with literature and database searches. Genotyping of the selected loci was performed with the Agena Bioscience MassARRAY® platform on 96 cases (58 schizophrenia and 38 bipolar I disorder patients) and 44 controls of Afrikaner, Sotho, and Tswana descent. Association analysis was performed by comparing and combining population and phenotype groups. Significant (p < 0.05) loci in the ADAMTSL1, CACNA1B, CACNA1C, CDH13, CTNNA2, RBFOX1, and TRIO genes were identified as possible susceptibility factors, and differences were observed with the association between population and phenotype groups. Through further pathway analysis, the calcium and cadherin-catenin pathways were identified as possible role players in the aetiology of schizophrenia and bipolar I disorder. The study represented an essential step towards understanding the genetic contribution towards schizophrenia and bipolar I disorder in distinct population groups and has the potential to contribute towards the knowledge base and inform future research efforts.