Association of Human Endogenous Retrovirus HERV-K18 Variant with Bipolar Disorder Type I

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.

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.

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).

This is the first study implying that HERV-K18 variations may be associated with the pathogenesis of BD-I.