Molecular epidemiology and transmission of hepatitis B virus in close family contacts of HBV-related chronic liver disease patients

There is limited data on the patterns of HBV mutation in family contacts of chronic liver disease (CLD) patients in India. DNA sequence analysis is an important tool to study this viral epidemiology. Transmission and prevalence of mutations in the S and pre-C gene region in HBV infected close family contacts of HBV-related CLD patients were studied. Twelve HBsAg(+) index patients and their 20 HBV DNA contacts were studied in detail. The S ORF and the pre-C region were sequenced using direct PCR products. S-gene sequencing included 32 specimens (12 index cases and all 20 contacts). Pre-C gene sequencing included 26 specimens (12 index cases and all the 14 HBsAg(+) contacts irrespective of their HBeAg status). More than 98% sequence homology was found between the index patients and their contacts. The in-depth study of 12 families revealed that the transmission pattern was primarily horizontal in 6 (50%) and vertical in 2 (17%) families (P < 0.05). The remaining four families had evidence of both horizontal and vertical transmission. Mutations in the S-gene were found in 80% of HBsAg(+) and 17% HBsAg(-) subjects (P < 0.05). A total of 22-point mutations at different nucleotide positions were found. In these, 16 (72%) were mutation of the "a" determinant region and 14 (64%) resulted in missense mutations. The commonest S-gene mutations were T118V and A128V, present in 44 and 38% specimens, respectively. T143M and G145R mutations in the second loop of the "a" determinant were found in 9% of the specimens. Novel mutations, C137stp and C138stp were found in only one HBsAg(-) subject. Mutations in the pre-C gene were common (91%) in patients with HBeAg(-) phenotype. G1896A mutation was found in 7 of 11 (64%) specimens changing amino acid tryptophane (W) to stop codon. Other mutations were at codons 25 and 29. The results of the study, demonstrate (1) clustering of Pre-C and S-gene mutations in the families, (2) horizontal mode of transmission and a common source infection appears to be frequent as evidenced by sequence homology and detailed history, (3) T118V and A128V were the commonest mutations in the S-gene region, while (4) M2 (G1896A) was the commonest pre-C gene mutation, and (5) long-term follow-up evaluation of these mutations suggested.