Genetic factors related to unconjugated hyperbilirubinemia amongst adults

Some variations in the UDP-glucuronosyltransferase 1A1 (UGT1A1) gene are involved in the development of unconjugated hyperbilirubinemia. We hypothesize that other genetic factors may also be associated with this disease. A total of 227 adults with normal routine haematology and liver function (apart from bilirubin testing for which they revealed bilirubin > or = 25.7 micromol/l and unconjugated bilirubin/total bilirubin > or = 80%), and 235 sex- and age-matched controls, were recruited. All subjects were analysed for UGT1A1, glucose-6-phosphate dehydrogenase (G6PD) and organic anion transporter polypeptide 2 (OATP2) genotypes using polymerase chain reaction-restriction fragment length polymorphism. The results indicated that G6PD deficiency, variant UGT1A1 gene and variant OATP2 gene were risk factors for hyperbilirubinemia. The odds ratios (OR) (with 95% confidence interval) were 220.83 (34.68-1406.30), 73.61 (17.01-318.63), 45.15 (11.19-182.22), 15.46 (4.35-54.99) and 6.51 (1.83-23.09), respectively, for individuals featuring the common UGT1A1/OATP2 haplotypes homozygous/heterozygous, compound heterozygous/heterozygous, compound heterozygous/wild-type, heterozygous/heterozygous and heterozygous/wild-type variations amongst subjects with normal G6PD activity. Amongst the subjects with G6PD deficiency, the OR was 159.00 (24.57-1028.94) for individuals carrying variations in both UGT1A1 and OATP2 genes. The UGT1A1/OATP2 haplotypes homozygous/wild-type, homozygous/compound heterozygous and homozygous/homozygous for G6PD normal and variant/wild-type for G6PD deficient individuals were only observed in the case group, and not in the control group. Amongst hyperbilirubinemic adults, bilirubin values tended to parallel variation status of their haplotypes. Adults featuring certain haplotypes in UGT1A1, OATP2 and G6PD genes face a high risk of developing unconjugated hyperbilirubinemia.     

Variations of the bilirubin uridine-diphosphoglucuronosyl transferase 1A1 gene in healthy Taiwanese

The activity of uridine-diphosphoglucuronosyl transferase 1 (UGT1) may influence the concentration of serum bilirubin. Because UGT1 is too labile to be measured with classical biochemical methods, we analysed the whole UGT1A1 gene in 290 healthy Taiwanese adults by using the polymerase chain reaction method, and investigated the relationship between UGT1A1 genotypes and serum bilirubin levels. The results showed that slightly more than 50% of the subjects had one or more variant sites in UGT1A1 gene. The most common variant was A(TA)6TAA/A(TA)7TAA (6/7) in the promoter area, followed by heterozygous variation within the coding region, compound heterozygous and homozygous variations. Among the four variant sites within the coding region, 211 G to A was the predominate one, 1091 C to T was a novel variation, and 686 C to A was associated with 6/7. Subjects with 6/7 or heterozygous variation within the coding region or compound heterozygous (plus one homozygous) variation had significantly higher bilirubin levels than those with wild UGT1A1 gene. When the 290 subjects were stratified into six groups according to their serum bilirubin concentrations, the bilirubin levels were correlated well to the frequencies of variant UGT1A1 gene. Our results show that there is a strong association between UGT1A1 gene and bilirubin levels in healthy Taiwanese adults. The occurrence of A(TA)7TAA allele was relatively rare and the variation rate within the coding region was much higher in Taiwanese compared to that in Caucasians.     

Predicting the risk of sporadic elevated bilirubin levels and diagnosing Gilbert's syndrome by genotyping UGT1A1*28 promoter polymorphism

Elevated fluctuating levels of bilirubin are a common problem in clinical studies. Differentiation between a drug-related adverse event and the diagnostic symptom for Gilbert's syndrome (GS), an idiopathic unconjugated hyperbilirubinemia, is more or less impracticable since the diagnosis of GS is by exclusion. The aim of this investigation was to evaluate the correlation of unspecific elevated bilirubin levels and the occurrence of GS with a described polymorphism in the uridine diphosphat glucuronosyltransferase 1A1 (UGT1A1) in a predominately Caucasian population. 304 volunteers (152 male, 152 female) were genotyped for the UGT1A1 promoter polymorphism by PCR amplification and polyacrylamide gel electrophoresis. Serum bilirubin levels and liver enzymes were determined and GS was diagnosed using clinico-chemical criteria. 23/13 subjects displayed the homocygote variant, 73/66 the heterozygote variant and 56/72 wildtype (male/female, respectively). 23 male and 3 female volunteers fulfilled the clinical criteria for GS (15.1, respectively 2.0%). Men exhibited higher serum bilirubin levels than women with a mean (SD) of 14.37 (8.92) micromol/l compared to 10.17 (5.37) micromol/l, respectively (p < 0.001). The homocygote mutant promoter length correlated well with serum bilirubin levels and with the clinical diagnosis of GS (p < 0.001 each). Genotyping of the UGT1A1 promoter polymorphism is a cheap and unequivocal method for predicting elevated and fluctuating bilirubin levels. It is better suited to this purpose than the clinical diagnosis which is based on exclusion. The genotyping of UGT1A1 promoter polymorphism can help to improve safety and the reliable assessment of adverse events in clinical studies. Our data additionally support the demand to refine the bilirubin reference values.     

Single-step identification of all length polymorphisms in the UGT1A1 gene promoter

AIM: To provide a sensitive genetic screening method for rapid identification of all known length polymorphisms in the promoter region of the uridine 5'-diphosphoglucose glucuronosyltransferase (UGT) 1A1 gene comprising (TA)5, (TA)7 and (TA)8 repeats as opposed to the non-mutated (TA)6 allele. METHODS: The UGT1A1 promoter genotype was assessed in 115 subjects by means of a newly developed pyrosequencing method. PCR-generated DNA templates of heterozygous (TA)5 and (TA)7 carriers were cloned into a TOPO TA vector and verified by sequencing. In addition, a (TA)8 segment was produced by cloning to demonstrate the ability of the method to detect this mutation. RESULTS: All length polymorphisms of the UGT1A1 promoter described in the literature were clearly identified. Fifteen subjects had Gilbert's syndrome with elevated serum bilirubin associated with a homozygous (TA)7TAA/(TA)7TAA genotype. Two subjects with the rare genotypes (TA)5TAA/(TA)6TAA and (TA)5TAA/(TA)7TAA were found, where only the latter one displayed elevated serum bilirubin levels. Allelic frequencies were 0.9%, 66.1% and 33% for the (TA)5TAA, (TA)6TAA and (TA)7TAA allele, respectively. CONCLUSION: Our method enables reliable genetic single-step screening for all known length polymorphisms in the UGT1A1 gene promoter that cause Gilbert's syndrome. This facilitates pharmacogenetic-guided dosing of drugs with known toxicity metabolized by UGT1A1.     

Morphine glucuronide-to-morphine plasma ratios are unaffected by the UGT2B7 H268Y and UGT1A1*28 polymorphisms in cancer patients on chronic morphine therapy

OBJECTIVE: UDP-glucuronosyltransferase (UGT) 2B7 is the major UGT isoform responsible for the 3- and 6-glucuronidation of morphine in humans. Studies in rats have indicated that UGT1A1 may also contribute to the formation of morphine 3-glucuronide (M3G). Our objective was to investigate whether the UGT2B7 H268Y and UGT1A1*28 polymorphisms contribute to the variability in morphine glucuronide-to-morphine plasma ratios among cancer patients undergoing analgesic therapy with morphine. METHODS: Seventy patients with normal hepatic and renal function using slow-release morphine to relieve cancer pain were included. UGT2B7 genotyping was performed using restriction enzyme analysis of polymerase chain reaction (PCR)-amplified DNA fragments. Wild-type and variant alleles of the UGT1A1 gene were identified using sizing of PCR-amplified fragments. Morphine 6-glucuronide (M6G)/morphine, M3G/morphine, and M3G/M6G plasma ratios were compared between genotypes. RESULTS: The M3G/morphine, M6G/morphine, and M3G/M6G plasma ratios varied 16-, 42-, and sevenfold, respectively, among individuals. No statistically significant differences in plasma ratios were found between individuals possessing UGT2B7 H/H ( n=20), H/Y ( n=30), or Y/Y ( n=20) genotypes. Five patients were homozygous for the UGT1A1 TA(7) allele, which is associated with reduced UGT1A1 gene expression. However, the mean M3G/M6G and M3G/morphine plasma ratios in TA(7) homozygous subjects did not differ significantly from those of heterozygous or homozygous wild-type (TA(6)) individuals. CONCLUSION: The UGT2B7 H268Y polymorphism cannot account for the considerable variation in glucuronide-to-morphine ratios in cancer patients. Moreover, the contribution of UGT1A1 to the formation of M3G appears to be of minor biological significance, at least in a UGT2B7 background.     

Polymorphisms of UDP-glucuronosyltransferase and pharmacokinetics of irinotecan.

Irinotecan is a prodrug that is hydrolyzed by carboxylesterase in vivo to form an active metabolite SN-38. SN-38 is further conjugated and detoxified by UDP-glucuronosyltransferase (UGT) to yield its beta-glucuronide (SN-38G). Although irinotecan is widely used, the drug causes unpredictably severe, occasionally fatal, toxicity of leukopenia or diarrhea. Interindividual variation of sensitivity to irinotecan is related to large variations of biotransformation of the active metabolite SN-38, some of which would be caused by genetic polymorphism of UGT1A1, an isozyme responsible for the SN-38 glucuronidation. As a surrogate for the UGT activity, the polymorphic frequency distribution of the area under the concentration-time curve (AUC) ratios of SN-38 to SN-38G (AUC(SN-38)/AUC(SN-38G)) using pooled pharmacokinetic data from four independent study groups in Japan was explored. The data from 100 cancer patients was analyzed, including 14 who were genotyped for UGT1A1 gene in the previous studies. The median ratios of AUC(SN-38)/AUC(SN-38G) was 0.40 (interquartile range, 0.30 to 0.55; range, 0.09 to 2.32). Frequency distribution of the AUC (SN-38)/AUC(SN-38G) was skewed to the right without bimodality and the patient population could not be segregated into discrete subgroups that differ in the UGT activity by the AUC ratios. The 4 subjects carrying UGT1A1*28 allele had values of the AUC(SN-38)/AUC(SN-38G) above the 75th percentile of the total population, suggesting a potential pharmacogenetic/pharmacokinetic relationship. Ordinary values with a median of 0.41 (interquartile range, 0.33 to 0.49) were obtained for the UGT1A1*6 heterozygous patient and the 9 UGT1A1*1 homozygous patients (the reference sequence). The large variation in the UGT activity being related to the genetic status would warrant pharmacogenetic-guided dosing of irinotecan.     

UDP-glucuronosyltransferase (UGT1A1*28 and UGT1A6*2) polymorphisms in Caucasians and Asians: relationships to serum bilirubin concentrations.

Polymorphisms that alter UDP-glucuronosyltransferase (UGT) activities have been identified. Mutations in the promoter of the UGT1A1 gene (UGT1A1*28), resulting in 5, 7 or 8, instead of 6 thymine-adenine (TA) repeats, alter bilirubin conjugation. Two missense mutations on one allele of UGT1A6 (UGT1A6*2) result in T181A and R184S amino acid substitutions and reduced activity against phenolics, such as 4-nitrophenol, 4-hydroxycoumarin and butylated hydroxy anisole. We determined the frequency of these polymorphisms in 245 healthy men and women, aged 20-40 years and examined the relationship between TA repeat number and serum bilirubin concentrations in a subset of 24 Asians and 169 Caucasians. The frequencies of the UGT1A1*28 genotypes were 0.537, 0.348, 0.098, 0.008 and 0.008 for promoter TA repeats 6/6, 6/7, 7/7, 5/6 and 6/8, respectively. Both allele and genotype frequencies varied by race (P < 0.02), with 11% of the Caucasians and none of the Asians having the 7/7 genotype. Within both ethnic groups, serum bilirubin increased with increased numbers of UGT1A1 promoter TA repeats (P = 0.0001). However, a strong ethnic group-by-UGT1A1 genotype interaction suggests that additional ethnic differences in bilirubin metabolism contribute to observed bilirubin concentrations. Genotype frequencies for UGT1A6*2 were 0.478, 0.392, 0.029, 0.090, 0.012 for wild-type (wt)/wt, wt/T181A + R184S, wt/R184S, T181A + R184S/T181A + R184S and T181A + R184S/R184S, respectively. The co-occurrence of polymorphisms in UGT1A1 and UGT1A6 differed from that expected (P < 0.0001): individuals homozygous wild-type for UGT1A1 and UGT1A6 were observed at twice the expected frequency; individuals homozygous variant for both genes were ten-fold more frequent and individuals homozygous wild-type for one gene and homozygous variant for the other were ten-fold less frequent than expected. Overall, 8% were homozygous variant for both UGT1 polymorphisms and 43% had at least one variant allele for both UGT1A1*28 and UGT1A6*2. These highly prevalent polymorphisms, which result in modified expression and activity of UGTs, may influence susceptibility to cancers associated with altered metabolism of endogenous and xenobiotic compounds.     

Glucuronidation of acetaminophen is independent of UGT1A1 promotor genotype

The metabolism of acetaminophen (paracetamol) is thought to be altered in patients with Gilbert's syndrome (GS), a chronic unconjugated hyperbilirubinemia. The underlying cause of GS is a polymorphism in the promotor region of the uridine diphosphate glucuronosyltransferase isoform 1A1 gene (UGT1A1*28), its encoded enzyme being responsible for the glucuronidation of bilirubin and presumably acetaminophen. Decreased enzyme activity results in elevated bilirubin levels and may activate various metabolic pathways leading to higher amounts of potentially hepatotoxic acetaminophen metabolites. Patients with GS might be more susceptible to unexpected side effects while taking acetaminophen and other drugs which are substrates of UGT1A1. The possibility of a correlation between glucuronidation capacity with respect to acetaminophen, UGT1A1 promotor polymorphism and the bilirubin serum level were investigated in 23 healthy male volunteers selected for UGT1A1 genotype (6 wildtypes, 9 mutants and 8 heterozygotes). One gram acetaminophen was administered p.o. and urine was collected over 2 4-hour periods. Unchanged acetaminophen and its glucuronide metabolite were determined using HPLC. The metabolic ratios unchanged acetaminophen/acetaminophen glucuronide in UGT1A1-wildtypes, heterozygotes and mutants showed no statistically significant differences. An association between metabolic ratio and serum bilirubin level could not be detected in any of the urine collection periods. These data confirm that there is no correlation between the capacity to glucuronidate acetaminophen, the UGT1A1 genotype and the bilirubin serum level. Acetaminophen is likely to be substrate of a UGT isoform other than the UGT1A1.     

Clinical pharmacology and pharmacogenetics of flavopiridol 1-h i.v. infusion in patients with refractory neoplasms

A phase I trial of flavopiridol administered as a 1-h i.v. infusion schedule was explored. Fifty-five patients were treated with flavopiridol at doses ranging from 12 to 78 mg/m2 daily for 5, 3 and 1 day every 3 weeks. Pharmacokinetic and pharmacodynamic analysis was performed together with analysis of a promoter polymorphism of the UGT1A1 gene. Peak concentrations and areas under the time-concentration curve of flavopiridol were linear within the doses studied. Estimated clearance was 13.8+/-4.9 l/h/m2 (mean+/-SD), volume of distribution at steady-state was 64.9+/-43.4 l/m2 and elimination half-life was 5.2+/-4.9 h. Forty-nine of the 55 patients were genotyped for the promoter polymorphism. We found five (10%) homozygous and 11 (22%) heterozygous patients for UGT1A1*28, which alters the reference sequence (TA)6TAA to the variant (TA)7TAA by an extra TA dinucleotide insertion within the TATA box. One patient was heterozygous for the sequence of five TA repeats, (TA)5TAA. The remaining 32 patients did not have the UGT1A1*28 allele (homozygous for the reference sequence). Associations of the UGT1A1 promoter genotype with either the pharmacokinetic parameters or diarrhea (occurrence and severity) were not observed in this study. The pharmacogenetic analyses did not support that the UGT1A1 promoter polymorphism could affect flavopiridol pharmacokinetics and alter the incidence and severity of diarrhea induced by the drug.     

UGT1A1基因多态性对宝安地区女性妊娠期甲状腺功能减退的临床价值

目的:探究尿苷二磷酸葡萄糖醛酸转移酶1A1（UGT1A1）基因多态性对宝安地区女性妊娠期甲状腺功能减退的临床价值。方法:以2021年1月至2022年2月就诊于深圳市宝安区石岩人民医院妊娠期甲状腺功能减退的女性100例为观察组,同时选取同期产检甲状腺功能正常的健康女性100例为对照组。取所有研究对象的空腹静脉血,进行RN...     

浙江台州地区使用伊立替康人群UGT1A1基因多态性相关性研究

目的 研究浙江台州地区使用伊立替康（CPT-11）人群UGT1A1基因多态性和不良反应的相关性。方法 以使用含CPT-11化疗的132例台州地区汉族肿瘤患者为研究对象,取其外周血提取基因组DNA,进行UGT1A1基因多态性检测。结果 132例以CPT-11为基础化疗方案的台州地区肿瘤患者中UGT1A1*28 TA（6/6）野生型93例（70.45%）,TA（6/7）杂合突变型共36例（27.27%）,TA（7/7）纯合突变型仅3例（2.27%）;UGT1A1*6 G/G野生型共97例（73.48%）,G/A杂合突变型共35例（26.52%）,未找到A/A纯合突变型。UGT1A1*28非野生型（6/7+7/7）患者发生腹泻的概率显著高于野生型患者（P=0.040）。而粒细胞减少、血小板减少、血红蛋白减少与UGT1A1*28基因多态性无显著性差异。迟发性腹泻、粒细胞减少、血小板减少、血红蛋白减少水平与UGT1A1*6基因多态性无显著性差异。结论 浙江台州地区UGT1A1基因突变频率较高,TA（6/6）野生型人群相比TA（6/7）和TA（7/7）,CPT-11使用后的腹泻风险增加。建议浙江台州地区肿瘤患者使用CPT-11化疗前进行UGT1A1基因多态性检测,以预测患者对CPT-11的耐受性,保证化疗的顺利进行。     

The polymorphism A118G of the human mu-opioid receptor gene decreases the pupil constrictory effect of morphine-6-glucuronide but not that of morphine.

Large individual differences in the clinical response to morphine therapy have been known for a long time by clinicians. The recent advances in genomic research encourage the search for pharmacogenetic causes of that variability. As a measure of central opioid effects, pupil diameters were assessed every 20 min for 18 h after administration of morphine or its active metabolite morphine-6-glucuronide (M6G) in a two-way crossover study. The opioid effects were compared between six subjects with a single-nucleotide polymorphism (SNP) A118G in the mu-opioid receptor gene (five heterozygous, one homozygous) and six control subjects. Non-parametric pharmacokinetic-pharmacodynamic modelling was employed to identify the influence of the A118G SNP on the concentration-response relationship of M6G and morphine, which was described by a sigmoid Emax model. As a measure of potency, the EC50 of the pupil constrictory effects of M6G was 714 +/- 197 nmol/l in wild-type and 1475 +/- 424 nmol/l in heterozygous carriers of the A118G SNP. In the homozygous carrier of the SNP, it had an EC50 of 3140 nmol/l. In addition, the dose-response relationship was flatter in the A118G carriers than in control subjects (shape factor of the sigmoid Emax model: gamma = 3.3 +/- 1.2, 1.7 +/- 0.5 and 1.6 for wild-type, heterozygous and the homozygous A118G carriers, respectively). In contrast, the concentration-response relationship of morphine was not affected by this specific SNP. The A118G SNP in the mu-receptor gene significantly reduces the potency of M6G in humans.     

UGT1A1*6 基因多态性与IP 方案治疗广泛期小细胞肺癌患者临床疗效和毒副反应的相关性分析

目的：探讨尿苷二磷酸葡萄糖醛酸转移酶1A1＊6（UGT1A1＊6）基因多态性与IP方案治疗的广泛期小细胞肺癌（ED-SCLC）患者临床疗效和毒副反应的相关性。方法选择2010年3月至2013年4月我院应用IP方案治疗的46例ED-SCLC患者,化疗前采全血提取基因组DNA,PCR法扩增目的基因片段,焦磷酸测序法测定UGT1A1＊6的基因多态性,化疗过程中观察并分析患者的临床疗效及不良反应的发生情况,探讨UGT1A1＊6基因多态性与不良反应和疗效之间的关系。结果46例患者中,UGT1A1＊6位点野生型G/G 34例（73％）,杂合突变型G/A 8例（17％）,纯合突变型A/A 4例（8％）。化疗期间,突变杂合型（G/A）及纯合突变型（A/A）患者3-4级腹泻和中性粒细胞减少的发生率明显高于UGT1A1野生型（G/G）（P〈0.05）,UGT1A1＊6各种基因型之间血小板减少的发生率比较,差异无统计学意义（P〉0.05）。结论 UGT1A1＊6基因多态性与IP方案治疗ED-SCLC发生严重的腹泻和中性粒细胞减少有关,但与其临床疗效无关。     

Human UGT1A6 pharmacogenetics: identification of a novel SNP, characterization of allele frequencies and functional analysis of recombinant allozymes in human liver tissue and in cultured cells

BACKGROUND: UDP-glucuronosyltransferase (UGT) enzymes catalyze the glucuronidation and typically inactivation of endogenous and exogenous molecules including steroid hormones, bilirubin and many drugs. The UGT1A6 protein is expressed predominantly in liver and metabolizes small phenolic drugs including acetaminophen, salicylates and many beta-blockers. Interindividual variation in the capacity of humans to glucuronidate drugs has been observed. RESULTS: We have identified a novel common single nucleotide polymorphism (SNP) in the human UGT1A6 gene resulting in a Ser7Ala change in encoded amino acid. We have further functionally characterized that polymorphism in the context of two previously reported polymorphisms, Thr181Ala and Arg184Ser. These non-synonymous cSNPs define four common haplotypes. Alleles appear with similar frequencies in Caucasian and African-American populations with distributions adhering to Hardy-Weinberg equilibrium. UGT1A6 genotype, rate of substrate glucuronidation and level of immunoreactive UGT1A6 protein was determined. A 25-fold variation in the rate of substrate glucuronidation and an 85-fold variation in level of immunoreactive protein were measured. Liver tissue samples that were homozygous for UGT1A6*2 exhibited a high rate of glucuronidation relative to tissues with other genotypes. Biochemical kinetic studies of recombinant UGT1A6 expressed in HEK293 cells indicated that the UGT1A6*2 allozyme, expressed homozygously, had almost two-fold greater activity toward p-nitrophenol than UGT1A6*1 and when expressed heterozygously (UGT1A6*1/*2) it was associated with low enzyme activity. CONCLUSIONS: These data suggest that common genetic variation in human UGT1A6 confers functionally significant differences in biochemical phenotype as assessed in human tissue and cultured cells expressing recombinant allozymes. This genetic variation might impact clinical efficacy or toxicity of drugs metabolized by UGT1A6.     

Neonatal jaundice and bilirubin UDP-glucuronosyl transferase 1A1 gene polymorphism in Turkish patients

Bilirubin uridine diphosphate-glucuronosyltransferase (B-UGT) is the rate-limiting enzyme for the conjugation of bilirubin with glucuronic acid in its excretion process into the bile. Variations in B-UGT gene (UGT-1A1) have been related to disorders characterised by hyperbilirubinaemia. The aim of this study was to investigate whether the number of thymine-adenine repeats in the promoter region of UGT-1A1 was related to non-physiologic hyperbilirubinemia of unexplained aetiology in Turkish newborns. These patients (n=106) were genotyped for their thymine-adenine repeat number in the promoter region of UGT-1A1, and were divided into two groups according to their bilirubin level. Forty-nine newborns with bilirubin levels higher than 17 mg/dl within the first ten days of life comprised the hyperbilirubinaemia group and 25 newborns with bilirubin levels higher than 10 mg/dl after fifteen days of life formed the prolonged jaundice group. Thirty-two newborns were included as healthy controls. The observed frequencies for the wild-type six repeat allele thymine-adenine (TA(6)) within each subject group were similar (P>0.05; 75.5%, 78.0% and 73.4%, respectively). Likewise, the distribution of TA(6/6), TA(6/7) and TA(7/7) genotypes among three groups were similar. These results imply that the TA(7) repeat allele of UGT1A1 (UGT1A1*28) is a common variant in the Turkish population. Our results do not suggest an association between thymine-adenine repeat polymorphism of UGT1A1 and hyperbilirubinaemia of unexplained aetiology or prolonged jaundice in Turkish neonates.     

UGT1A polymorphisms in a Swedish cohort and a human diversity panel, and the relation to bilirubin plasma levels in males and females

Objectives The objective of this study was to investigate the prevalence of different polymorphisms and haplotypes associated with individual variations in pharmacokinetics and drug toxicity in the uridine-diphosphate glucuronosyl transferase (UGT) 1A gene in a Swedish cohort (248 healthy volunteers) and in 14 different ethnic groups. We also estimated UGT1A genotype-dependent glucuronidation efficiency using the endogenous substrate bilirubin as an indicator.Methods Pyrosequencing-based genotyping assays were used to determine the different polymorphisms and haplotypes.Results Haplotype analysis of the UGT1A1 (*1*28), UGT1A6 (*1*2), and UGT1A7(*1*2*3*4) allelic variants showed that three major haplotypes constituted 84% of the allelic variants in the cohort. We identified 15 haplotypes altogether from all groups, including previously undescribed haplotypes.Testing for the association of genotype and total bilirubin levels (nonfasting) in plasma disclosed that homozygous carriers of the TA allele, irrespective of haplotype combinations, had increased levels of bilirubin compared with noncarriers, but a gender-associated difference was observed.Conclusions In a Swedish cohort, several genetic variants in the UGT1A gene are common, but prevalence in a population may differ because of ethnicity. A phenotype based on bilirubin levels has limitations in serving as an indicator of pharmacogenetic differences in glucuronidation due to the influence of gender. Because of possible substrate overlap regarding different UGT1A isoforms, determination of haplotypes of potential cis-acting polymorphisms in the UGT1A gene should be considered in pharmacogenetic association studies regarding drugs that undergo glucuronidation.     

Identification and characterization of a functional TATA box polymorphism of the UDP glucuronosyltransferase 1A7 gene

UDP glucuronosyltransferases (UGT) detoxify bilirubin and therapeutic drugs, a process influenced by single nucleotide polymorphisms (SNPs) in their structural genes and promoter elements. UGT1A1*28 is a functional UGT promoter polymorphism associated with Gilbert's disease and severe irinotecan toxicity, which also occurs in the absence of UGT1A1*28. The aim of this study was to identify and characterize UGT promoter variants relevant for irinotecan detoxification. Recombinant UGT1A proteins were analyzed for irinotecan metabolite glucuronidation by UGT activity assays. In 427 healthy blood donors and 71 homozygous UGT1A1*28 carriers, the 5'-untranslated region of the UGT1A7 gene locus was studied. An SNP was detected by allelic discrimination and characterized by reporter gene experiments. A novel -57 T--> G SNP with a gene frequency of 0.39 in healthy blood donors was identified in the putative TATA box of the UGT1A7 gene, reducing promoter activity to 30%. It is in linkage dysequilibrium with a variant of the UGT1A7 first exon that is present in the reduced-activity UGT1A7*3 and UGT1A7*4 alleles. Homozygous UGT1A1*28 carriers simultaneously carried this variant in 97%. We identified a novel reduced-function TATA box SNP of the UGT1A7 gene that catalyzes irinotecan metabolite detoxification. Its association with variants of the UGT1A1 promoter and UGT1A7 gene may influence irinotecan metabolism. Our finding emphasizes the importance of combinations of structural and regulatory gene polymorphisms that may be useful as markers of drug toxicity.     

UDP-Glucuronosyltransferase 1A1 gene polymorphisms and total bilirubin levels in an ethnically diverse cohort of women.

The objective of this study was to investigate variations in UGT1A1 polymorphisms and haplotypes among African-American and Caucasian women and to assess whether variants other than UGT1A1*28 are associated with total serum bilirubin levels. The (TA)(n) repeats and 14 single nucleotide polymorphisms (SNPs) in the UGT1A1 gene were genotyped in 335 African Americans and 181 Caucasians. Total serum bilirubin levels were available in a subset of 125 women. Allele frequencies of all SNPs and (TA)(n) repeats were significantly different between African Americans and Caucasians. In Caucasians, three common haplotypes accounted for 71.8% of chromosomes, whereas five common haplotypes accounted for only 46.6% of chromosomes in African Americans. Mean total serum bilirubin levels were significantly lower (p = 0.005) in African Americans (0.36 mg/dl) than in Caucasians (0.44 mg/dl). The (TA)(n) repeats explained a significant amount of variation in total bilirubin levels (R(2) = 0.27, p < 0.0001), whereas other SNPs were less correlative. Thus, significant variations in UGT1A1 haplotype structure exist between African Americans and Caucasians in this relatively large cohort of women. The correlation of UGT1A1 with total bilirubin levels was mainly due to (TA)(n) repeats in Caucasians but a clear correlation was not observed in African Americans because of the high diversity of haplotypes and the small sample size. These data have implications for the design of epidemiologic studies of cancer susceptibility and pharmacogenetic studies for adverse drug reactions in populations of African ancestry.