Risk of Liver Cirrhosis Associated with Genotypes and Mutants of HBV

目的 目前研究普遍認為，在預測肝硬化、肝細胞癌與B型肝炎相關肝臟疾病之預後，血中B 型肝炎病毒量為一強而有力的預測因子。然而在與病毒本身相關的其他因子中，病毒基因型及和e 抗原合成量相關之病毒突變株，在相關肝臟疾病病程中所扮演的角色仍有待釐清。本研究乃以前瞻性世代研究法來探討B 型肝炎病毒B、C基因型、precore stop codon G1896A 突變和basal core promoter A1762T/G1764A 雙突變對於發生肝硬化的影響。 方法 研究世代建立於1991至1992年間，參與對象為台灣七個鄉鎮市區30至65歲的居民，而本研究係針對當中2,692名B 型肝炎表面抗原陽性、C 型肝炎抗體陰性且未接受過抗病毒藥物治療的世代成員進行分析。個案在納入研究世代之初的血清進行B 型肝炎病毒量和病毒基因型之檢測，而病毒量達104 copies/mL 以上者再另外檢測血清中是否存在B型肝炎病毒 G1896A 和A1762T/G1764A突變株。肝硬化診斷工具為腹部超音波，並排除進入研究半年內之肝硬化新發個案。 結果 截至2004年6月30日止，共追蹤了30,939人年，個案平均追蹤時間為11.5年，追蹤期間有305個肝硬化新發個案。個案肝硬化的發生率(每十萬人年)在感染B基因型與C基因型病毒者中分別為768.2 和 1,585.3；帶有precore野生型及突變株G1896A個案的發生率分別為1,985.7 和 881.0；帶有BCP野生型及突變株 A1762T/G1764A 個案的發生率則為912.6 和 2,210.2。在調整了性別、年齡、抽煙、喝酒、e抗原與ALT狀態和B型肝炎病毒量後，感染基因型C者相對於感染基因型B者發生肝硬化的風險比(hazard ratio)為1.7 (95%信賴區間：1.4-2.2）；帶有precore G1896A突變株相對於其野生型的風險比為0.6（95%信賴區間：0.4-0.9）；而帶有BCP A1762T/G1764A突變株相對於其野生型的風險比為1.9 （95%信賴區間：1.4-2.5）。 結論 B 型肝炎病毒C 基因型以及BCP A1762T/G1764A突變株是肝硬化的危險因子，而precore G1896A突變株則對肝硬化的發生具有保護作用。Objective Although HBV DNA level has been shown to be an independent risk predictor for liver cirrhosis, the roles of HBV genotype and mutants in the progression of liver cirrhosis remain unclear. The aim of this study was to investigate the risk of cirrhosis associated with genotype, precore stop codon G1896A mutation and A1762T/G1764A double mutation in the basal core promoter (BCP) of hepatitis B virus (HBV). Methods A cohort of 2,692 untreated participants (aged 30–65), who were HBsAg(+) and anti-HCV-seronegative, was enrolled from seven townships in Taiwan between 1991 and 1992. Serum samples at cohort entry were tested for HBV viral load and genotype. A sub-cohort of 1,477 participants with HBV DNA levels ≥ 104 copies/mL was further tested for HBV mutants of G1896A and A1762T/G1764A. Newly developed liver cirrhosis cases were diagnosed by ultrasonography. Results Up to June 30, 2004, 305 newly diagnosed cirrhosis cases had occurred during 30,939 person-years of follow-up, with a mean follow-up time of 11.5 years. The incidence rates per 100,000 person-years for participants infected with HBV genotype B and C were 768.2 and 1,585.3, respectively. For participants infected with wild and mutant type HBV precore stop codon 1896, rates were 1,985.7 and 881.0, respectively; and for participants infected with wild and typical mutant type HBV BCP 1762/1764, rates were 912.6 and 2,210.2, respectively. After adjustment for gender, age, cigarette smoking, alcohol consumption, HBeAg status, ALT level, and HBV viral load, the hazard ratio (95% confidence interval) of liver cirrhosis was 1.7 (1.4–2.2) for genotype C compared with genotype B, 0.6 (0.4–0.9) for G1896A mutant compared with wild type, and 1.9 (1.4–2.5) for A1762T/G1764A mutant compared with wild type. Conclusion HBV genotype C and A1762T/G1764A mutants were risk factors for liver cirrhosis, while the emergence of G1896A mutant seemed to have a protective effect on the progression of liver cirrhosis.TABLE OF CONTANTS 中文摘要..................................................i ABSTRACT................................................iii LIST OF TABLES...........................................vi LIST OF FIGURES.........................................vii INTRODUCTION..............................................1 Liver Cirrhosis..........................................1 HBV Genotype.............................................2 HBV Mutants..............................................3 Precore Mutation.........................................4 Basal Core Promoter Mutation...........................5 METHODS...................................................7 Study Population.........................................7 Interview and Blood Collection...........................8 Laboratory Analysis......................................8 Ascertainment of Cirrhosis..............................10 Data Analysis...........................................11 RESULTS..................................................13 Characteristics of the Study Participants...............13 Prevalence of HBV Genotype and Mutants by Risk Factors..13 Incidence Rates and Cumulative Incidence................14 Multivariable –adjusted HRs............................16 Subgroups Analysis......................................16 Combined Effects of Precore and BCP Mutants.............17 DISCUSSION...............................................19 REFERENCES...............................................25 TABLES...................................................31 FIGURES..................................................4