Nucleic Acid Sequence Analysis of the Precore Region of Hepatitis B Virus From Sera of Southern African Black Adult Carriers of the Virus

Abstract

an indicator of active viral replication and high levels of infecOur purpose was to ascertain if mutations of the pretivity. HBeAg negativity and hepatitis B e antigen antibody core region of the hepatitis B virus genome, in particular (anti-HBe) positivity are used as markers of decreased viral the 1896 stop codon mutation, are responsible for the replication and resolution of inflammation. 3 Precore muta-95% hepatitis B e antigen (HBeAg)-negativity rate in tions that abolish HBeAg expression without a concomitant southern African black adult carriers. Hepatitis B virus decrease in viral replication have, however, been described. (HBV) DNA was extracted from the serum of 57 asymp-A guanine (G) to adenine (A) transition at nucleotide 1896 of tomatic carriers (42 HBeAg-negative; 15 HBeAg-posithe precore region, resulting in a translational stop codon, is tive), the precore region was amplified using the polythe mutation that most often prevents HBeAg expression. 4,5 merase chain reaction (PCR), and sequenced. SixOther stop codon, translation-initiation codon, or frameshift carriers (14.6%) had mutations known to prevent HBeAg mutations are detected rarely. 5-9 synthesis: 4 involved the precore initiation codon (1814),The HBeAg-minus mutation caused by the 1896 transition and one created a stop codon at 1874. The 1896 mutation is present in almost all patients with anti-HBe-positive, occurred alone in one carrier only (2.4%). The infre-HBV DNA-positive chronic hepatitis in Italy, 8,10 Greece, 4 quency of the 1896 mutation can be explained by the Bulgaria, 11 Spain, 12 and Japan. 5 This mutation occurs less high prevalence (70%) of the adw subtype in the carriers frequently in North America, 13 France, 14-16 the United Kingstudied. Inter alia, adw differs from ayw in that codon dom, 17 and China. 18,19 is comprised of CCC instead of CCT. The presenceAlthough a few black Africans have been included in invesof C instead of T in position 1858 precludes the G-to-A tigations conducted in countries to which they have mimutation at 1896 because the coexistence of these two grated, 20-22 the prevalence of precore mutants of HBV in this mutations would destabilize the stem-loop structure of population has not been formally determined. the RNA encapsidation signal, a finding confirmed by HBV infection is hyperendemic in southern African blacks. our observation that the CCC polymorphism and the A feature of chronic carriers of HBV in this population is 1896 mutation were mutually exclusive. Ten HBeAg-negthat only 5% are still HBeAg-positive by the time they reach ative carriers (24%) had a missense mutation at position adulthood, 23 compared with higher rates of 40% or more in 1862 in the bulge of the RNA encapsidation signal, which other hyperendemic areas of the world. 24 The reason for the may possibly affect HBeAg expression by interfering high rate of HBeAg negativity is not known. Thus, the purwith either priming of reverse transcription or signal pose of this study was to determine whether mutations in peptide cleav...

High Prevalence of 1762T 1764A Mutations in the Basic Core Promoter of Hepatitis B Virus Isolated From Black Africans With Hepatocellular Carcinoma Compared With Asymptomatic Carriers

“…The precore region in Southern African isolates of HBV, studied previously in the same sera, 8,9 showed significantly less nucleotide and amino acid divergence than did the BCP. This was true in both ASCs and patients with HCC.…”

“…Nucleotide sequencing of the precore region of HBV isolates from a number of countries has shown the 1896 stop codon mutation to be a frequent cause of the HBeAgnegative phenotype, 5,6 with other nonsense or frame-shift mutations accounting for a small proportion (reviewed in Miyakawa et al 7 ). However, these mutations are seldom present in black African carriers in Southern Africa 8,9 and our focus has shifted to the X open reading frame.…”

Novel Hepatitis B Virus Genotype A Subtyping Assay That Distinguishes Subtype Aa from Ae and Its Application in Epidemiological Studies

“…Infection with HBV/Aa is associated with low prevalence of HBeAg in serum and early seroconversion (14,15). Recently Ahn and coworkers showed that the T1809/T1812 mutations interfere with the translation of HBeAg in vitro and may be responsible for the early loss of HBeAg seen in southern African black carriers of HBV (1).…”

“…This subtype has also been found in HBV isolates from Malawi (29). In African countries, genotype A isolates, most of which are subtype AЈ, seem to be associated with low levels of HBV DNA in serum and a low prevalence of hepatitis B e antigen (HBeAg) in serum (14,15). On the other hand, HBV carriers infected with isolates belonging to the remainder of genotype A, distributed widely in European countries and the United States, have a higher rate of sustained remission after seroconversion and a lower rate of death related to liver disease than other genotypes during long-term follow-up (8,24,33).…”

Point Mutations Upstream of Hepatitis B Virus Core Gene Affect DNA Replication at the Step of Core Protein Expression

“…In this regard, a G1862T substitution is frequently detected in patients following seroconversion to anti-HBe (14,33). This point mutation converts residue 17 of the precore peptide, the Ϫ3 position of the signal peptidase cleavage site, to phenylalanine.…”