The Association of HHV-6 and the TNF-α (-308G/A) Promotor with Major Depressive Disorder Patients and Healthy Controls in Thailand

Abstract

Major depressive disorder (MDD) is a silent global health problem that can lead to suicide. MDD development is suggested to result from numerous risk factors, including genetic factors. A precise tool for MDD diagnosis is currently not available. Recently, inflammatory processes have been identified as being strongly involved in MDD development and the reactivation of human herpesvirus type 6 (HHV-6), upregulating cytokines such as TNF-α, which are associated with MDD. Therefore, this study aimed to determine the association of HHV-6 with genetic factors, especially TNF-α mutation, in MDD patients and their relatives compared to healthy controls. The Patient Health Questionnaire (PHQ-9) was used to evaluate MDD status, and 471 oral buccal samples were investigated for HHV-6 infection and viral copy number by qPCR. TNF-α (-308G/A) gene mutation and the cytokines TNF-α, IL-6, and IL-10 were analyzed by high-resolution melting (HRM) analysis and enzyme-linked immunosorbent assay (ELISA). Whole-exome sequencing of buccal samples was performed to analyze for genetic factors. The results showed significantly higher HHV-6 positivities and viral loads in MDD patients (15/59 (25.67%) and 14,473 ± 16,948 copies/µL DNA) and their relatives (blood relatives 17/36 (47.22%) and 8146 ± 5656 copies/µL DNA); non-blood relatives 7/16 (43.75%) and 20,721 ± 12,458 copies/µL DNA) compared to the healthy population (51/360 (14.17%) and 6303 ± 5791 copies/µL DNA). The TNF-α (-308G/A) mutation showed no significant difference. Surprisingly, 12/26 (46.15%) participants with the TNF-α (-308G/A) mutation showed HHV-6 positivities at higher rates than those with wild-type TNF-α (-308G) (70/267 (26.22%)). HHV-6-positive participants with TNF-α (-308G/A) showed higher levels of TNF-α, IL-6, and IL-10 than those of negative control. Exome analysis revealed that common mutations in immune genes were associated with depression. Therefore, this study unveiled the novel association of inflammatory gene TNF-α (-308G/A) mutations with HHV-6 reactivation, which could represent a combined risk factor for MDD. This result could induce further research on MDD development and clinical applications.

Keywords: HHV-6; TNF-α; inflammation; major depressive disorder (MDD).

Figure 1

Specimens.

Figure 2

The association of HHV-6 with MDD patients, blood relatives, and non-blood relatives. Remark: red color = separate between HHV-6 positive and negative in MDD group.

Figure 3

Risk factors for MDD, MDD without HHV-6, MDD with HHV-6. Remark: red = statistically significant, green = not statistically significant when associated with MDD compared to healthy control.

Figure 4

PHQ-9 level of healthy individual control and MDD patients in HHV-6 positive and negative cases (percentage).

Figure 5

The association of HHV-6 positivity with TNF-α promotor status. Remark: red = number of samples.

Figure 6

The association of HHV-6 and TNF-α promotor status with cytokine expression measured using ELISA and HHV-6 viral load. N = normal healthy control. Healthy: positive/G, positive/G/A, negative/G/A, negative/G; and MDD patients being treated with drugs: positive/G, negative/G were available for ELISA analysis. (A) IL-6 cytokine level, (B) IL-10 cytokine level, (C) TNF-α cytokine level, and (D) HHV-6 viral load. * p-value < 0.05, ** p-value < 0.01 and *** p-value < 0.001.

Figure 7

Whole-exome sequencing comparison of mutations of MDD patients, their relatives, and healthy controls. Underlines indicate them only being detected in MDD patients.