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Division of Gastroenterology, Department of Internal Medicine, Graduate Institute of Clinical Medicine, Hepatitis Research Center
Department of Medical Research, National Taiwan University College of Medicine and National Taiwan University Hospital, Taipei, Taiwan
Chan et al. reported in the June issue of the Journal of Infectious Diseases their interesting results regarding the epidemiological and virological characteristics of 2 subgenotypes of hepatitis B virus (HBV) genotype C [1]. They found that genotype C strains isolated from 80% of HBV carriers in Hong Kong belong to a subgroup that is prevalent in Southeast Asia and has been designated subgenotype "Cs." The HBV strains in the remaining 20% of patients belong to another subgenotype, "Ce," which is more common in the Far East. Subgenotype Ce is characterized by a T at nucleotide position 1858 (T1858), whereas Cs has a C at the same position (C1858). Compared with subgenotype Ce, subgenotype Cs is associated with a higher prevalence of basal core promoter (BCP) mutations and a lower prevalence of precore stop-codon mutations. At the same time, Chan et al. indicated that both BCP mutations and genotype C are closely related to the development of hepatocellular carcinoma (HCC) [2, 3]. Nevertheless, the relative contribution of BCP mutations and genotypes to the development of HCC should be further examined. Chan et al. further observed that the relationship between BCP mutations and HCC is strongest in areas where the background prevalence of BCP mutations is low, as it is in Taiwan [2], but that it is weaker in areas where the background prevalence of BCP mutations is high, as in Hong Kong [4]. Because the background prevalence of BCP mutations is likely related to the distribution of HBV genotype C subgenotypes, Chan et al. speculated that the inconsistent relationship between BCP mutations and the development of HCC might be due to the varied distribution of HBV genotype C subgenotypes in different geographic areas. Thus, in addition to studying HBV genotype and BCP mutations, it is important to examine the relative prevalence of HBV subgenotype Cs and Ce in different areas.
In Taiwan, we have studied the prevalence of nucleotide C1858 versus T1858 in patients infected with genotype C [5]. We found that, of 39 patients with genotype C, 37 (95%) carried HBV T1858 (most likely subgenotype Ce), and only 2 (5%) carried C1858 (most likely subgenotype Cs) (table 1), which suggests that subgenotype Cs is rare in Taiwan. Thus, the association between BCP mutations and the development of HCC could not be explained by the differential distribution of HBV genotype C subgenotypes, as was suggested by Chan et al. [1]. More large studies are needed to examine the clinical impact of HBV subgenotypes on the pathogenesis and progression of liver diseases.
References
1. Chan HLY, Tsui SKW, Tse C-H, et al. Epidemiological and virological characteristics of 2 subgroups of hepatitis B virus genotype C. J Infect Dis 2005; 191:202232. First citation in article
2. Kao JH, Chen PJ, Lai MY, Chen DS. Basal core promoter mutations of hepatitis B virus increase the risk of hepatocellular carcinoma in hepatitis B carriers. Gastroenterology 2003; 124:32734. First citation in article
3. Kao JH, Chen PJ, Lai MY, Chen DS. Hepatitis B genotypes correlate with clinical outcomes in patients with chronic hepatitis B. Gastroenterology 2000; 118:5549. First citation in article
4. Chan HLY, Hui AY, Wong ML, et al. Genotype C hepatitis B virus infection is associated with increased risk of hepatocellular carcinoma. Gut 2004; 53:14948. First citation in article
5. Kao JH, Chen PJ, Lai MY, Chen DS. Clinical and virological aspects of blood donors infected with hepatitis B virus genotypes B and C. J Clin Microbiol 2002; 40:225. First citation in article