Association of Human Endogenous Retrovirus HERV-K18 Variant with Bipolar Disorder Type I
Zeynep Yegin1, Gokhan Sarisoy2, Cumhur Avsar3, Ayse Erguner Aral2, Haydar Koc4
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 Statistics, Faculty of Science, Cankiri Karatekin University, Cankiri, Turkey
Correspondence to: Zeynep Yegin
Medical Laboratory Techniques Program, Vocational School of Health Services, Sinop University, Sinop 57000, Turkey
E-mail: zyegin1@gmail.com
ORCID: https://orcid.org/0000-0003-4637-0253
Received: September 2, 2024; Revised: November 9, 2024; Accepted: December 10, 2024; Published online: January 16, 2025.
© The Korean College of Neuropsychopharmacology. All rights reserved.

This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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 (odds ratio, 5.386; 95% confidence interval, 1.602−18.110). 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; Endogenous retroviruses; HERV-K18; Genetic variation


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