Association of human endogenous retrovirus HERV-K18 variant with bipolar disorder type I
Zeynep Yegin 1*, Gokhan Sarisoy 2, Cumhur Avsar 3, Ayse Erguner Aral 4, Haydar Koc 5
1Medical Laboratory Techniques Program, Vocational School of Health Services, Sinop University, Sinop, Turkey, 2Department of Psychiatry, Faculty of Medicine, Ondokuz Mayıs University, Samsun, Turkey, 3Department of Biology, Faculty of Arts & Sciences, Sinop University, Sinop, Turkey, 4Department of Psychiatry, Faculty of Medicine, Ondokuz Mayıs University, Samsun, Turkey, 5Department of Statistics, Faculty of Science, Cankiri Karatekin University, Cankiri, Turkey
Received: August 22, 2024; Revised: November 9, 2024; Accepted: December 10, 2024; Published online: December 10, 2024.
© The Korean College of Neuropsychopharmacology. All rights reserved.

Abstract
Objective: Human endogenous retroviruses (HERVs) and associated sequences occupy ~8% of the human genome and dysregulation of HERV transcripts may have significant impacts on human health including psychiatric disorders. HERV-K18 is still active in the human genome and its envelope gene encodes a superantigen (SAg) which may result in deregulation of the immune system. In the study, the possible associations of the two variants localized in the SAg-coding region of HERV-K18 with bipolar disorder type I (BD-I) were evaluated.
Methods: The subjects included 100 patients with BD-I and 100 age- and sex-matched healthy controls. The effects of the two HERV-K18 variants (HERV-8594 and HERV-8914) were analyzed with Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) method. The possible associations of the genotypes/alleles in BD-I patients with several clinical and demographic data were also evaluated.
Results: HERV-8914 TT genotype had approximately 5.36 times higher risk of BD-I than those with the CC genotype (OR=5.386, 95% CI=1.602-18.11). Moreover, the prevalence of the CC genotype in patients with hypomania (31.25%) was found to be higher than that observed in patients without hypomania (10.71%) (Fisher’s Exact test= 5.931, p=0.036).
Conclusion: This is the first study implying that HERV-K18 variations may be associated with the pathogenesis of BD-I.
Keywords: Bipolar disorder, human endogenous retrovirus (HERV), HERV-K18, genetic variation

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