Nucleotide mutations associated with hepatitis B e antigen negativity

Synergistic impact of mutations in Hepatitis B Virus genome contribute to its occult phenotype in chronic Hepatitis C Virus carriers

We characterized occult HBV (OHBV) from hepatitis B surface antigen (HBsAg)-negative chronic HCV carriers of Eastern India to explore the impact of genomic variability of HBV in causing undetectability of HBsAg and low viremia that define the occult phenomenon. Screening of sera samples revealed the presence of OHBV in 17.8% of HCV-infected patients. Determination of full-length OHBV sequences and comparison with that from HBsAg-positive carriers led to the detection of distinct substitutions/mutations in PreS2, S, P and X ORFs and in X-promoter and Enhancer-II of OHBV. These mutations were introduced in wild-type HBV and their effects were evaluated by transfection in Huh7 cells. In vitro assays demonstrated that S-substitutions resulted in antigenically modified HBsAg that escaped detection by immunoassays whereas those in ORF-P caused significant decline in viral replication. Impairment in Enhancer-II and X-promoter activities were noted due to occult-associated mutations that generated reduced pregenomic RNA and intracellular HBV-DNA. Additionally, Enhancer-II mutations altered the small to large surface protein ratio and diminished extracellular HBV-DNA and HBsAg secretion. Further, mutations in PreS2, X and enhancer-II increased Grp78-promoter activity, suggesting that OHBV could trigger endoplasmic reticulum stress. Thus viral mutations contribute synergistically towards the genesis of occult phenotype and disease progression.

Basal core promoter, precore region mutations of HBV and their association with e antigen, genotype, and severity of liver disease in patients with chronic hepatitis B in India

Spontaneous mutations of hepatitis B virus (HBV) could influence the severity of liver disease. Since the basal core promoter (BCP) and the precore (Pc) regions are important for viral replication, these regions were examined for naturally occurring mutations and were correlated with the genotype, e antigen status, and severity of liver disease. In 82 patients with histologically confirmed chronic hepatitis B, the BCP and Pc regions were sequenced and aligned with known wild-type sequences. Sequence based HBV genotyping was done and HBV DNA was quantified. Thirty-three (40%) patients had decompensated chronic liver disease and the remaining patients had chronic hepatitis B. Forty-six (56%) patients were HBeAg positive. HBV genotype A was found in 28%, D in 65%, and B/C in 7.3%. The Pc G1896A mutation was more common in HBeAg-negative (33% vs. 2%, P < 0.01) patients and was genotype D specific. The Pc G1862T mutation was detected more often in HBeAg-positive than HBeAg-negative (37% vs. 11%, P < 0.01) patients and was genotype A specific (P < 0.01). BCP mutations at the 1,762/64 nucleotide positions were common in HBeAg negative than positive (36% vs. 13%, P < 0.05) and were equally common in different genotypes. TA 1-3 region mutations of the BCP were significantly higher in HBeAg-negative as compared to HBeAg-positive patients (78% vs. 26%, P < 0.01). BCP mutations had significantly higher HBV DNA levels. It is concluded that Pc G1862T mutant is Genotype A-specific but is not always associated with e antigen. The TA 1-3 rich mutations of BCP region are also associated with the absence of e antigen in Indian patients.