尿苷二磷酸葡萄糖醛酸基转移酶 (UDPGT) 是负责将胆红素与胆红素单葡萄糖苷酸和二葡萄糖苷酸结合的一种酶;因此,它是胆红素结合的限速步骤。这主要发生在肝细胞的内质网中。有 5 个外显子最终导致 UDPGT 产生。外显子 1 确定底物特异性。至少有 13 种不同类型的外显子 1。外显子 1a 编码 UDPGT-1A1 的可变区,该酶负责与胆红素结合。[7]Chowdhury RJ, Chowdhury RN, Jansen P. Bilirubin metabolism and its disorders. In: Boyer TD, Wright TL, Manns MP, eds. Zakim and Boyer's hepatology. Philadelphia, PA: Saunders Elsevier; 2006:1449-1485.外显子 1a 的上游有一个 TATAA 盒启动子区。TATAA 区的正常序列为 A[TA]6TAA。吉尔伯特综合征患者遗传了启动子区的不同序列,主要表达一个比 A[TA]6TAA 更长的序列,称为 A[TA]7TAA。[1]Watson KJ, Gollan JL. Gilbert's syndrome. Balliere's Clin Gastroenterol. 1989;3:337-355.http://www.ncbi.nlm.nih.gov/pubmed/2655758?tool=bestpractice.com在导致吉尔伯特表型的 UDPGT-1A1 编码区内,已发现其他突变。[4]Burchell B, Hume R. Molecular genetic basis of Gilbert's syndrome. J Gastroenterol Hepatol. 1999;14:960-966.http://www.ncbi.nlm.nih.gov/pubmed/10530490?tool=bestpractice.com[5]Takeuchi K, Kobayashi Y, Tamaki S, et al. Genetic polymorphisms of bilirubin uridine diphosphate-glucuronosyltransferase gene in Japanese patients with Crigler-Najjar syndrome or Gilbert's syndrome as well as in healthy Japanese subjects. J Gastroenterol Hepatol. 2004;19:1023-1028.http://www.ncbi.nlm.nih.gov/pubmed/15304120?tool=bestpractice.com[8]Monaghan G, Ryan M, Seddon R, et al. Genetic variation in bilirubin UDP-glucuronosyltransferase gene promoter and Gilbert's syndrome. Lancet. 1996;347:578-581.http://www.ncbi.nlm.nih.gov/pubmed/8596320?tool=bestpractice.com
还有证据表明,UDPGT-1A1 变体(主要是 UDPGT-1A1* 28)患者可能存在蛋白酶抑制剂代谢异常,因此在利用阿扎那韦治疗期间可能出现严重的伊立替康毒性或黄疸。有证据表明,这些突变在霍奇金淋巴瘤和心血管病的发展中提供了保护作用。[9]Strassburg CP. Gilbert-Meulengracht’s syndrome and pharmacogenetics: is jaundice just the tip of the iceberg? Drug Metab Rev. 2010;42:162-175.http://www.ncbi.nlm.nih.gov/pubmed/20070246?tool=bestpractice.com[10]Minucci A, Concolino P, Giardina B, et al. Rapid UGT1A1 (TA)(n) genotyping by high resolution melting curve analysis for Gilbert’s syndrome diagnosis. Clin Chim Acta. 2010;411:246-249.http://www.ncbi.nlm.nih.gov/pubmed/19932091?tool=bestpractice.com
在接受托珠单抗(一种白介素-6 受体的单克隆抗体)治疗的类风湿关节炎患者中,也曾经报告该变体 (UDPGT-1A1*28) 被描述为与高间接胆红素血症的发生有关。在接受该药治疗的这些患者中,尚未发现其他重度肝毒性证据。[11]Lee JS, Wang J, Martin M, et al. Genetic variation in UGT1A1 typical of Gilbert syndrome is associated with unconjugated hyperbilirubinemia in patients receiving tocilizumab. Pharmacogenet Genomics. 2011;21:365-374.http://www.ncbi.nlm.nih.gov/pubmed/21412181?tool=bestpractice.com已针对 UDPGT-1A1 变体进行了一项观察研究,尤其是在接受聚乙二醇干扰素和利巴韦林治疗的丙型肝炎患者中。与未携带该变体的患者相比,由于利巴韦林,这些患者可能出现更高的间接胆红素水平。这种现象与肝毒性并不相关。[12]Deterding K, Grüngreiff K, Lankisch TO, et al. Gilbert's syndrome and antiviral therapy of hepatitis C. Ann Hepatol. 2009;8:246-250.http://www.ncbi.nlm.nih.gov/pubmed/19841506?tool=bestpractice.com