Major depressive disorder (MDD) is a global health concern with a complex etiology involving genetic, environmental and infectious factors. The exact cause of MDD remains unknown. The present study explored the association between genetic factors, human herpesvirus 6 (HHV‑6) and MDD. The present study analyzed single nucleotide polymorphisms (SNPs) and HHV‑6 viral load in oral buccal samples from patients with MDD (with and without blood relatives with MDD) and healthy controls. The study used high‑resolution melt analysis to examine rs40184 (C>T) in the solute carrier family 6 member 3 (SLC6A31) gene, rs6265 (C>T) in the brain‑derived neurotrophic factor (BDNF) gene and rs9383046 (G>A) in the jumonji and AT‑rich interaction domain‑containing 2 (JARID2) gene. HHV‑6 infection and viral load was assessed using the quantitative PCR. Whole‑exome sequencing was used to examine SNPs. The variant alleles of SNPs rs40184 [18/40 (45.00) vs. 29/238 (12.55%)] and rs6265 [30/54 (55.46) vs. 117/292 (40.06%)] were significantly more common in patients with MDD than in healthy controls, indicating they may be probable hereditary risk factors for MDD. HHV‑6 positivity was significantly more common in carriers of the G/A genotype (12/15, 80%) than carriers of the G/G genotype (75/363, 20.7%) for rs9383046, implying that genetic variations may affect HHV‑6 risk and MDD onset. Similarly, HHV‑6 viral loads were significantly higher in carriers of the G/A genotype (99,990.85±118,392.64 copies/ng DNA) than carriers of the G/G genotype (48,249.30±101,216.28 copies/ng DNA) for rs9383046. Whole‑exome sequencing identified two SNPs in JARID2 (rs11757092 and rs9383050) associated with MDD, highlighting its genetic complexity. The present study helps explain the complex interactions between HHV‑6 infection, genetics and MDD onset, improving understanding of how SNPs in JARID2 contribute to HHV‑6 infection and MDD onset; these findings may impact future approaches to diagnosing and treating MDD.

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