Haplotype structure of the UDP-glucuronosyltransferase 1A1 (UGT1A1) gene and its relationship to serum total bilirubin concentration in a male Korean population

Nutrition in Gilbert's Syndrome-A Systematic Review of Clinical Trials According to the PRISMA Statement

Gilbert syndrome is the most common hyperbilirubinemia, associated with a mutation in the UGT1A1 bilirubin gene, which produces an enzyme that conjugates bilirubin with glucuronic acid. Episodes of jaundice occurring in GS negatively affect patients' quality of life. This systematic review aimed to analyze clinical studies regarding nutrition in people with GS. The study followed the PRISMA guidelines and utilized the Ebsco, Embase, Cochrane, PubMed, Scopus, and Web of Science databases to search clinical trials focused on diet/nutrition in GS (1963-2023 years). The methodological quality of selected studies was assessed using the Jadad scale. As a result, 19 studies met the inclusion criteria. The research mainly focused on the impact of caloric restriction, consumption of various diet variants, and vegetables and fruits on hyperbilirubinemia and metabolic health. A nutritional intervention consisting of not applying excessive calorie restrictions and consuming fats and biologically active compounds in vegetables and fruits (Cruciferae, Apiaceous, Rutaceae) may prevent the occurrence of jaundice episodes. It is justified to conduct further research on detecting such compounds in food, which, by influencing the expression of the UGT liver enzyme gene, could contribute to regulating bilirubin concentration in the blood of people with GS.

Bilirubin metabolism and UDP-glucuronosyltransferase 1A1 variants in Asians: Pathogenic implications and therapeutic response

In the Asian general population, at least six single-nucleotide variants (SNVs) in the UDP-glucuronosyltransferase (UGT) 1A1 gene have been identified: -3279T>G, -53A(TA)₆ TAA>A(TA)₇ TAA, 211G>A, 686C>A, 1091C>T, and 1456T>G. Each of these six SNVs was observed in at least four ethnic groups of the 12 Asian populations studied. In East Asian populations, the descending frequency of these six SNVs was as follows: -3279G>[-53A(TA)₇ TAA, 211A]>(686A, 1091T)>1456G. Because of the presence of linkage disequilibrium and the expulsion phenomenon, when the SNVs -3279G, -53A(TA)₇ TAA, 211A, and 686A were simultaneously involved, 15 instead of the estimated 81 genotypes were observed. Those carrying 686AA or 1456GG developed Gilbert's syndrome or Crigler-Najjar syndrome type 2. Both -53A(TA)₇ TAA/A(TA)₇ TAA and 211AA are the main causes of Gilbert's syndrome in East Asian populations. In East Asian populations, the 211AA genotype is the main cause of neonatal hyperbilirubinemia, whereas -53A(TA)₇ TAA/A(TA)₇ TAA exerts a protective effect on hyperbilirubinemia development in neonates fed with breast milk. Both 211A and -53A(TA)₇ TAA are significantly associated with adverse drug reactions induced by irinotecan (one of the most widely used anticancer agents) in Asians. However, at least three common SNVs (-3279G, -53A(TA)₇ TAA, and 211A) should be comprehensively analyzed. This study investigated the clinical significance of these six SNVs and demonstrated that examining UGT1A1 variants in Asian populations is considerably challenging.

The frequency, clinical course, and health related quality of life in adults with Gilbert's syndrome: a longitudinal study

Background

Gilbert syndrome (GS) is an autosomal recessive inherited disorder of bilirubin glucuronidation which has not been investigated in Egypt. This longitudinal study investigated the frequency, clinical course, genetic profile and health related quality of life in Egyptian adults.

Methods

An initial cross-sectional study was conducted to assess the frequency of Gilbert syndrome among Egyptian adults. Subjects fulfilling the criteria of GS were enrolled into the study and prospectively followed for the clinical features, risk factors for hyperbilirubinemia, health related quality of life [Short form-36 Health Survey version 2 (SF-36v2) and Chronic Liver Disease Questionnaire (CLDQ)], vitamins assessment and UGT1A1 polymorphisms.

Results

One hundred and one subjects fulfilled the criteria of GS with a prevalence of 8.016%. Recurrent jaundice was the only presentation in 47 (56.627%) GS subjects and jaundice was associated with abdominal pain, dyspepsia or loss of appetite in 54 (53.465%) subjects. A significant difference in 25-Hydroxyvitamin D3 levels was detected between GS patients and control subjects (P <  00001). Twelve subjects with GS developed significant unconjugated bilirubinemia during direct antiviral therapy (DAAs) therapy for HCV despite achieving sustained virologic response. Pregnancy was associated with significant exacerbation of unconjugated bilirubin which persisted through pregnancy. Risk factors for clinical jaundice included general anesthesia, pregnancy, fasting > 12 h, pregnancy, and low calorie weight losing plans, systemic infections, and intensive physical effort. During jaundice attacks, subjects with GS had significant differences in vitality, role emotional, social functioning, worry and general health domains of the SF-36v2 and CLDQ compared to controls. The homozygous polymorphism A(TA)7TAA was the most frequent polymorphism in Egyptians with GS.

Conclusion

Gilbert syndrome is a frequent inherited disorder in Egypt. In a substantial percentage of subjects with GS, episodes of jaundice are associated with other symptoms and nutritional deficiencies which result in impairment of HRQOL. Screening, counseling, monitoring and individualized health care are recommended for subjects with GS in the setting of anesthesia, pregnancy, treatment with DAAs, deliveries, surgery and weight loss plans.

UGT1A1 gene and neonatal hyperbilirubinemia: a preliminary study from Bengkulu, Indonesia

Objective

The genetic involvement in unconjugated neonatal hyperbilirubinemia has been extensively studied. Despite the high incidence of hyperbilirubinemia in Indonesia, studies are lacking. The objective of this study is to elucidate the role of polymorphism in the UGT1A1 in Neonatal Hyperbilirubinemia in Bengkulu, Indonesia.

Results

There were 41 neonates enrolled in the study; 30 had a total serum bilirubin level ≥ 15 mg/dL (hyperbilirubinemia neonates) while 11 has < 15 mg/dL (control neonates). Genetic mutations in Exon 1, UGT1A1*6 (c211g > a) and one in promoter region, UGT1A1*60 (c3279t > g) were determined by polymerase chain reaction–restriction fragment length polymorphism. We found 18 (60%) mutation in exon 1 in hyperbilirubinemia group and 7 (64%) in the control group with an identical allele frequency of 0.3 in both groups. We found heterozygous UGT1A1*60 4 times (13.3%) and homozygous 26 times (86.7%) in the hyperbilirubinemia group, with an identical allele frequency of 0.935 in hyperbilirubinemia and 1 in control group. This study supports the involvement of genetic factors in the development of unconjugated hyperbilirubinemia in Bengkulu population.

Differences in UGT1A1 gene mutations and pathological liver changes between Chinese patients with Gilbert syndrome and Crigler-Najjar syndrome type II

Diagnosis of Crigler-Najjar syndrome type II (CNS-II) and Gilbert syndrome (GS) based on the serum bilirubin concentration is difficult, because this parameter can fluctuate under certain conditions. The aim of this study was to explore differences in UGT1A1 gene mutations, which cause both CNS and GS, and pathological changes between CNS-II and GS.Ninety-five Chinese patients with hereditary unconjugated hyperbilirubinemia were enrolled in this study. Peripheral blood samples obtained from patients were used to evaluate bilirubin levels and for UGT1A1 gene testing. Percutaneous needle biopsy of the liver and staining of tissue samples with hematoxylin and eosin, Masson trichrome, reticulin, and Perl Prussian blue were performed for 59 patients. The Ishak scoring system was used to assess inflammatory activity and the extent of fibrosis.One hundred ninety-two UGT1A1 mutations at 6 sites were detected in the 95 patients; the most common mutation in GS was c.-3279T>G in the phenobarbital response enhancing motif of the UGT1A1 promoter, whereas the most common mutation in CNS-II was p.G71R. The frequency of heterozygous p.G71R mutations in CNS-II was significantly higher than that in GS (P = .001); however, the frequency of homozygous c.-3279T>G mutations in CNS-II was markedly lower than that in GS (P = .032). Among all patients with multiple mutations, the frequency of p.Y486D was significantly higher in CNS-II than in GS (P = .007). The frequency of compound c.-3279T>G, A(TA)7TAA, and p.G71R mutations in CNS-II was significantly higher than that in GS (P = .001). Among the 59 patients who underwent percutaneous needle biopsy, 20 had iron deposition in the liver. The frequency of hepatic iron deposition in CNS-II was significantly higher than that in GS (P = .002).The linked polymorphic mutations, A(TA)7TAA and c.-3279T>G in UGT1A1, were most strongly associated with GS, whereas mutations in the coding region, especially p.G71R and p.Y486D, were more strongly associated with CNS-II. Iron deposition was more common in liver biopsies from patients with CNS-II than in those with GS.

Clinical Pharmacogenetic Testing and Application: Laboratory Medicine Clinical Practice Guidelines

Pharmacogenetic testing for clinical applications is steadily increasing. Correct and adequate use of pharmacogenetic tests is important to reduce unnecessary medical costs and adverse patient outcomes. This document contains recommended pharmacogenetic testing guidelines for clinical application, interpretation, and result reporting through a literature review and evidence-based expert opinions for the clinical pharmacogenetic testing covered by public medical insurance in Korea. This document aims to improve the utility of pharmacogenetic testing in routine clinical settings.

Association between the Specific UGT1A1 Promoter Sequence Variant (c-3279T>G) and Unconjugated Neonatal Hyperbilirubinemia

We investigated the association between c-3279T>G and unconjugated neonatal hyperbilirubinemia. In all, 141 neonates were recruited; 63 had hyperbilirubinemia necessitating treatment, and 78 with bilirubin < 7 mg/dl served as the control group. The frequency of occurrence of c-3279T > G allele was significantly higher in the hyperbilirubinemic (49.2%) than in the control group (25.6%). The homozygous (p = 0.001, OR = 17.7 and CI = 3.9-79.3) rather than the heterozygous state (p = 0.3, OR = 0.7 and CI = 0.3-1.6) was associated with hyperbilirubinemia. Among the hyperbilirubinemic group, comparison between the three genotypes, homozygous mutation, heterozygous mutation and the normal allele, revealed that the former was associated with significantly higher mean peak total serum bilirubin [mean ±  standard deviation (SD): 33.7 ± 8.2, 26.9 ± 2.8 and 21± 2.7, respectively, p-value = 0.0001], higher bilirubin/albumin ratio (p = 0.000) and a longer duration of hospital stay (p = 0.001). Homozygous c-3279T > G mutation represents an important risk factor for the development of neonatal hyperbilirubinemia.

Functional Study of Haplotypes in UGT1A1 Promoter to Find a Novel Genetic Variant Leading to Reduced Gene Expression

BACKGROUND

Uridine diphosphate glucuronyltransferase 1 family, A1 (UGT1A1) encodes for an enzyme that is a part of glucuronidation pathway, and a number of studies have shown that the promoter polymorphisms of UGT1A1 are associated with various diseases and drug response. In this study, we examined a possible association between UGT1A1 promoter haplotypes and the gene expression level.

METHODS

To identify promoter haplotype structure population, we directly sequenced the promoter region of UGT1A1 in 192 healthy Korean to identify 10 UGT1A1 promoter single-nucleotide polymorphisms (SNPs). Then, we genotyped the 10 SNPs in additional 192 non-Korean samples comprised of Chinese, Japanese, European American, and African American, and constructed haplotype structures. Furthermore, we conducted luciferase assay for the promoter SNP haplotypes to examine a possible expression change.

RESULTS

rs3755319C-rs2003569A-rs887829C-rs8175347(TA)6 (6.60 ± 0.15) and rs3755319A-rs2003569 G-rs887829C-rs8175347(TA)7 (2.79 ± 0.97) led to significantly lower gene expression when compared with rs3755319C-rs2003569 G-rs887829T-rs8175347(TA)6 (8.28 ± 0.60).

CONCLUSIONS

Our result suggests that the haplotypes in UGT1A1 promoter region can affect the expression level of the gene and drug metabolism associated with UGT1A1. Furthermore, in addition to rs8175347, rs3755319 was found to induce lower gene expression of UGT1A1.

Serum Total Bilirubin, not Cholelithiasis, is Influenced by UGT1A1 Polymorphism, Alpha Thalassemia and β(s) Haplotype: First Report on Comparison between Arab-Indian and African β(s) Genes

Background

We explored the potential relationship between steady state serum bilirubin levels and the incidence of cholelithiasis in the context of UGT1A1 gene A(TA)nTAA promoter polymorphism in Omani sickle cell anemia (SCA) patients, homozygotes for African (Benin and Bantu) and Arab-Indian β^S haplotypes, but sharing the same microgeographical environment and comparable life style factors.

Methods

136 SCA patients were retrospectively studied in whom imaging data including abdominal CT scan, MRI or Ultrasonography were routinely available. Available data on the mean steady state hematological/biochemical parameters (n=136), β^s haplotypes(n=136), α globin gene status (n=105) and UGT1A1 genotypes (n=133) were reviewed from the respective medical records.

Results

The mean serum total bilirubin level was significantly higher in the homozygous UGT1A1(AT)₇ group as compared to UGT1A1(AT)₆ group. Thus, not cholelithiasis but total serum bilirubin was influenced by UGT1A1 polymorphism in this SCA cohort.

Conclusion

As observed in other population groups, the UGT1A1 (AT)₇ homozygosity was significantly associated with raised serum total bilirubin level, but the prevalence of gallstones in the Omani SCA patients was not associated with α thalassaemia, UGT1A1 polymorphism, or β^s haplotypes.

Circulating Markers of Liver Function and Cardiovascular Disease Risk

Measurement of serum concentrations of various liver enzymes and other nonenzymatic proteins and metabolites of heme metabolism (eg, bilirubin) is often undertaken in clinical practice. Measurement of these liver function tests is simple, quick, and relatively inexpensive. However, interpreting the liver function test results in patients without evidence of liver disease is often challenging. Concentrations of some of liver enzymes, such as γ-glutamyltransferase or alkaline phosphatase, and concentrations of liver-derived metabolites, such as bilirubin, may be influenced by metabolic processes beyond the liver, sometimes making interpretation of the test results difficult. This scenario frequently occurs both in individuals at risk of cardiovascular disease and in patients with known cardiovascular disease, often resulting in the clinicians ignoring the test results. In this brief review, we discuss the evidence for associations between key serum liver function tests and cardiovascular disease risk and where associations are robust; we provide an interpretation for possible mechanistic links between the liver function test and cardiovascular disease.

Quantitative trait analysis of polymorphisms in two bilirubin metabolism enzymes to physiologic bilirubin levels in Chinese newborns

OBJECTIVE

To explore the effects of variants in Uridine Diphosphate Glucuronosyl Transferase 1A1 (UGT1A1) and Heme Oxygenase-1 (HMOX1) on daily physiological bilirubin levels and bilirubin changes during the first week after birth in Chinese newborns. Both UGT1A1 and HMOX1 code rate-limiting enzymes in the bilirubin metabolism pathway.

STUDY DESIGN

We conducted a retrospective quantitative trait study to analyze 4154 daily bilirubin values, 3129 bilirubin changes, and 11 polymorphisms of 988 newborns during the natural course of physiological hyperbilirubinemia.

RESULTS

For UGT1A1, we found minor allele A of rs4148323 (G211A, UGT1A1*6) contributed to higher daily bilirubin levels on days 4-6 (with contributions to variations increasing from 4.8% to 12.3%), minor allele T of rs887829 (c-364t) contributed to lower daily bilirubin levels for days 6 and 7 (with contributions to variations increasing from 7.0% to 10.2%) (P < .03 for all). In addition, minor alleles of rs887829 and (TA)n repeat (UGT1A1*28), and haplotype T-long-G at rs887829-(TA)n-rs4148323 were associated with a decrease in bilirubin levels from day 5 to day 6 (P < .01 for all). No contribution from HMOX1 was found.

CONCLUSION

Bilirubin levels and changes during the middle and late parts of the first week were attributed to variants and haplotypes in UGT1A1. This quantitative trait study may provide a more robust statistical method for determining the association of genetic factors and bilirubin kinetics to predict the development of neonatal bilirubin in early postnatal life.

Association analysis of UGT1A genotype and haplotype with SN-38 glucuronidation in human livers

AIM

7-ethyl-10-hydroxycamptothecin (SN-38), the active metabolite of irinotecan, is mainly eliminated hepatically through glucuronidation by UGT1A1 and UGT1A9 enzymes. This study comprehensively investigates the effects of UGT1A1 and UGT1A9 genetic polymorphism on SN-38 glucuronidation activity.

MATERIALS & METHODS

Genetic polymorphisms and combinational haplotypes of UGT1A1 and UGT1A9, SN-38 glucuronidation activities, and protein levels of UGT1A1 and UGT1A9 were determined using a set of over 45 Chinese livers.

RESULTS

UGT1A1 reduced function variants UGT1A1*6, *28, *60 and *1B exhibited additive effect. The number of UGT1A1 reduced function alleles was associated with decreased SN-38G formation rates and UGT1A protein levels. UGT1A9 I399C>T and UGT1A9*1b, which were highly linked, were associated with increased SN-38 glucuronidation activity and UGT1A protein levels. However, further analysis based on UGT1A9-1A1 haplotypes confirmed that their increased effect was partly due to their close linkage with UGT1A1 reduced function alleles.

CONCLUSION

UGT1A1 genetic polymorphisms have a more important function in human liver SN-38 glucuronidation activity than UGT1A9. Original submitted 7 November 2013; Revision submitted 30 January 2014.

Molecular Analysis of the UGT1A1 Gene in Korean Patients with Crigler-Najjar Syndrome Type II

PURPOSE

Crigler-Najjar syndrome type II (CN-2) is characterized by moderate non-hemolytic unconjugated hyperbilirubinemia as a result of severe deficiency of bilirubin uridine diphosphate-glucuronosyltransferase (UGT1A1). The study investigated the mutation spectrum of UGT1A1 gene in Korean children with CN-2.

METHODS

Five Korean CN-2 patients from five unrelated families and 50 healthy controls were enrolled. All five exons and flanking introns of the UGT1A1 gene were amplified by polymerase chain reaction (PCR) and the PCR products were directly sequenced.

RESULTS

All children initially presented with neonatal jaundice and had persistent indirect hyperbilirubinemia. Homozygous p.Y486D was identified in all five patients. Three patients had an associated homozygous p.G71R and two a heterozygous p.G71R. The allele frequency of p.Y486D and p.G71R in healthy controls was 0 and 0.16, respectively. No significant difference in mean serum bilirubin levels was found between homozygous carriers of p.G71R and heterozygous carriers.

CONCLUSION

The combination of homozygous p.Y486D and homozygous or heterozygous p.G71R is identified. The p.Y486D and p.G71R can be screened for the mutation analysis of UGT1A1 in Korean CN-2 patients.

Relation of conjugated bilirubin concentrations to the presence of coronary artery calcium

Whether conjugated bilirubin concentration, resulting from hepatic UDP-glucuronosyltransferase 1 A1 activity, is associated with cardiovascular disease is unknown. Our aim was to investigate the relation between serum conjugated bilirubin concentrations and coronary artery calcium score (CACS) as a measure of preclinical atherosclerosis. Data were analyzed from an occupational cohort of 14,583 subjects who underwent a cardiac computed tomographic estimation of CACS and measurements of risk factors. Logistic regression was used to describe associations between bilirubin concentrations and CACS. The proportion of subjects with a CACS >0 (total: men = 1,351, women = 111) decreased across increasing conjugated bilirubin quartiles (men p <0.001, women p = 0.005). After adjustment for age, gender, waist, systolic blood pressure, smoking, exercise, alcohol, homeostatic model assessment of insulin resistance, glucose, triglyceride, high- and low-density lipoprotein cholesterols, high-sensitivity C-reactive protein, lipoprotein (a), ferritin, fatty liver, cerebrovascular accident, coronary artery disease, hypertension, and diabetes, there was an inverse independent association between conjugated bilirubin and CACS >0 (odds ratio 0.76, 95% confidence interval 0.64 to 0.92, p = 0.004, for top vs bottom quartile). After further adjustment for estimated glomerular filtration rate, the odds ratio was 0.83 (95% confidence interval 0.69 to 0.99), p = 0.04. Exclusion of subjects with a high bilirubin (total >1.3 mg/dl) did not attenuate the association. In conclusion, there was a strong inverse and independent relation between conjugated bilirubin and CACS. The mechanism behind this association is not clear and may not be causal, but the effects of glucuronidation on cardiovascular disease risk should be tested.

The effect of UGT1A1 promoter polymorphism in the development of hyperbilirubinemia and cholelithiasis in hemoglobinopathy patients

Present study was aimed to explore the effect of (TA)n UGT1A1 gene promoter polymorphism on bilirubin metabolism, bilirubinaemia, predisposition to cholelithiasis and subsequent cholecystectomy, in Sickle-Cell Anemia (SCA) and beta-Thalasemia major (bTH) in Kuwaiti subjects compared to other population. This polymorphism was analyzed and correlated to total bilirubin and cholelithiasis in 270 age, gender, ethnically matched subjects (92 bTH, 116 SCA and 62 Controls) using PCR, dHPLC, fragment analysis and direct sequencing. Four genotypes of UGT1A1 were detected in this study (TA6/6, TA6/7, TA6/8 and TA7/7). (TA)6/8 was found only in four individuals; hence it was not included in the analysis. There was a statistically significant association of genotypes with serum total bilirubin levels in both bTH and SCA groups (p<0.001). Subjects with (TA)7/7 had the highest total serum bilirubin level (178.7 ± 3.5 µmole/l). A significant association was observed between allele (TA)7 and cholelithiasis development (p = 0.0001). The 40%, 67.5% and 100% of SCA with (TA)6/6, (TA)6/7 and (TA)7/7 respectively developed cholelithiasis and were subsequently cholecystectomized. Our results confirm UGT1A1 (TA)7 allele as one of the factors accounting for the hyperbilirubinemia and cholelithiasis observed in SCA and bTH.

New insights in bilirubin metabolism and their clinical implications

Bilirubin, a major end product of heme breakdown, is an important constituent of bile, responsible for its characteristic colour. Over recent decades, our understanding of bilirubin metabolism has expanded along with the processes of elimination of other endogenous and exogenous anionic substrates, mediated by the action of multiple transport systems at the sinusoidal and canalicular membrane of hepatocytes. Several inherited disorders characterised by impaired bilirubin conjugation (Crigler-Najjar syndrome type I and type II, Gilbert syndrome) or transport (Dubin-Johnson and Rotor syndrome) result in various degrees of hyperbilirubinemia of either the predominantly unconjugated or predominantly conjugated type. Moreover, disrupted regulation of hepatobiliary transport systems can explain jaundice in many acquired liver disorders. In this review, we discuss the recent data on liver bilirubin handling based on the discovery of the molecular basis of Rotor syndrome. The data show that a substantial fraction of bilirubin conjugates is primarily secreted by MRP3 at the sinusoidal membrane into the blood, from where they are subsequently reuptaken by sinusoidal membrane-bound organic anion transporting polypeptides OATP1B1 and OATP1B3. OATP1B proteins are also responsible for liver clearance of bilirubin conjugated in splanchnic organs, such as the intestine and kidney, and for a number of endogenous compounds, xenobiotics and drugs. Absence of one or both OATP1B proteins thus may have serious impact on toxicity of commonly used drugs cleared by this system such as statins, sartans, methotrexate or rifampicin. The liver-blood cycling of conjugated bilirubin is impaired in cholestatic and parenchymal liver diseases and this impairment most likely contributes to jaundice accompanying these disorders.

Distribution of selected gene polymorphisms of UGT1A1 in a Saudi population

INTRODUCTION

Glucuronidation is an important phase II pathway responsible for the metabolism of many endogenous substances and drugs to less toxic metabolites, which undergo renal excretion. The aim of the current work was to evaluate genotype and allele frequencies of certain UDP-glucuronosyltransferase 1A1 (UGT1A1) variants in an Arab population.

MATERIAL AND METHODS

Genomic DNA was isolated from 192 healthy unrelated Saudi males of various geographic regions and genotyping of UGT1A1*6, *27, *36, *28, *37, and *60 was carried out using polymerase chain reaction (PCR) amplification followed by direct sequencing.

RESULTS

The most common allele for (TA) repeats was the wild type (TA)6 with a frequency of 74.3% followed by the mutant (TA)7 (i.e., UGT1A1*28) with a frequency of 25.7%. The distribution of UGT1A1*60 allele was 62.4% among subjects with the homozygous mutant genotype of 35.4%, while the wild type variant represents 10.6% only. Both UGT1A1*6 and *27 were not detected as all screened subjects showed a homozygous wild type pattern. Similarly, UGT1A1*36* and *37 were either not present or rarely found, respectively. In comparison to other populations, the frequency of UGT1A1*60 and *28 in the studied population was less than that of African Americans but higher than Asians. The geographical origin of the study subjects also implied some differences in genotype distribution of (TA) repeats and UGT1A1*60.

CONCLUSIONS

Our data indicate that Saudis harbor some important UGT1A1 mutations known to affect enzyme activity. Additional studies are warranted to assess the clinical implications of these gene polymorphisms in this ethnic group.

Comprehensive analysis of UGT1A1 genetic polymorphisms in Chinese Tibetan and Han populations

The study of polymorphism of the UGT1A1 gene has not been reported in the Chinese Tibetan population, and there are no comparisons of genetic polymorphism in the gene between Chinese Han and Tibetan populations. In this study, we directly sequenced the functional regions of the UGT1A1 gene in 200 unrelated healthy Chinese volunteers, detecting 20 variations (including five novel ones). The distributions of allele and genotype frequencies differ between the two groups. UGT1A1*6 is the major reduced functional variant in the populations, and the *27 allele was detected only in the Han group. Differences in the frequencies of the UGT1A1*6/*63 genotype between the Tibetan and Han populations were statistically significant (P = 0.009). Our genetic data might provide fundamental information for the advance of personalized medicine and will facilitate genotype-phenotype studies in larger populations.

The dual role of pharmacogenetics in HIV treatment: mutations and polymorphisms regulating antiretroviral drug resistance and disposition

Significant intra- and interindividual variability has been observed in response to use of pharmacological agents in treatment of HIV infection. Treatment of HIV infection is limited by high rates of adverse drug reactions and development of resistance in a significant proportion of patients as a result of suboptimal drug concentrations. The efficacy of antiretroviral therapy is challenged by the emergence of resistant HIV-1 mutants with reduced susceptibility to antiretroviral drugs. Moreover, pharmacotherapy of patients infected with HIV is challenging because a great number of comorbidities increase polypharmacy and the risk for drug-drug interactions. Drug-metabolizing enzymes and drug transporters regulate drug access to the systemic circulation, target cells, and sanctuary sites. These factors, which determine drug exposure, along with the emergence of mutations conferring resistance to HIV medications, could explain variability in efficacy and adverse drug reactions associated with antiretroviral drugs. In this review, the major factors affecting the disposition of antiretroviral drugs, including key drug-metabolizing enzymes and membrane drug transporters, are outlined. Genetic polymorphisms affecting the activity and/or the expression of cytochromes P450 or UGT isozymes and membrane drug transport proteins are highlighted and include such examples as the association of neurotoxicity with efavirenz, nephrotoxicity with tenofovir, hepatotoxicity with nevirapine, and hyperbilirubinemia with indinavir and atazanavir. Mechanisms of drug resistance conferred by specific viral mutations are also reviewed, with particular attention to replicative viral fitness and transmitted HIV drug resistance with the objectives of providing a better understanding of mechanisms involved in HIV drug resistance and helping health care providers to better manage interpatient variability in drug efficacy and toxicity.

Phase II and UGT1A1 genotype study of irinotecan dose escalation as salvage therapy for advanced gastric cancer

Background:

To assess the efficacy and safety of individualised dose optimisation of irinotecan monotherapy as salvage treatment for advanced gastric cancer (AGC).

Methods:

A total of 43 patients were enrolled. Intravenous irinotecan (350 mg m⁻²) was administered every 3 weeks. The dose was increased (425 mg m⁻² and 500 mg m⁻²) or decreased (250 mg m⁻²) depending on patient tolerance. UGT1A1 genotypes were determined by direct sequencing of genomic DNA extracted from peripheral blood.

Results:

A total of 183 cycles of irinotecan were administered, with a median of four cycles per patient. The overall response rate was 9.3%, and the disease control rate was 62.8%. Median time to disease progression was 2.8 months, and median overall survival was 8.0 months. Grade 3–4 neutropenia was the most common toxicity (53.5%), and febrile neutropenia was the least common toxicity (4.6%). Compared with defective allele groups, UGT1A1 *1/*1 was associated with a lower incidence of grade 3–4 neutropenia during the first cycle (P=0.018).

Conclusion:

Individualised irinotecan dose escalation based on patient tolerance was not associated with increased toxicity and shows modest activity as salvage chemotherapy for AGC. The role of UGT1A1 genotype in clinical toxicity requires further evaluation.

Population differences in major functional polymorphisms of pharmacokinetics/pharmacodynamics-related genes in Eastern Asians and Europeans: implications in the clinical trials for novel drug development

Drug lag, recently discussed extensively in Japan, can be divided into two phases: clinical development time and application review time. The former factor is still an important problem that might be improved by promoting multi-regional clinical trials and considering the results from other similar populations with Japanese, such as Koreans and Chinese. In this review, we compare the allelic or genotype frequencies of 30 relatively common functional alleles mainly between Eastern Asians and Europeans as well as among 3 major populations in Eastern Asian countries, Japan, Korea, and China, in 12 pharmacokinetics (PK)/pharmacodynamics (PD)-related genes; CYP2C9 (*2 and *3), CYP2C19 (*2, *3 and *17), 13 CYP2D6 haplotypes including *4, *5 and *10, CYP3A5 (*3), UGT1A1 (*28 and *6), NAT2 (*5, *6 and *7), GSTM1 and GSTT1 null genotypes, SLCO1B1 521T>C, ABCG2 421C>A, and HLA-A*31:01 and HLA-B*58:01. In this review, differences in allele frequencies (AFs) or genotype frequencies (GFs) less than 0.1 (in the cases of highest AF (GF) ≥0.1) or less than 0.05 (in the cases of lowest AF (GF) <0.1) were regarded as similar. Between Eastern Asians and Europeans, AFs (or GFs) are regarded as being different for many alleles such as CYP2C9 (*2), CYP2C19 (*2, *3 and *17), CYP2D6 (*4 and *10), CYP3A5 (*3), UGT1A1 (*28 and *6), NAT2 (*5*7), GSTT1 null and ABCG2 421C>A. Among the 3 Eastern Asian populations, however, only AFs of CYP2C19*3, CYP2D6*10, HLA-A*31:01 and HLA-B*58:01 are regarded as dissimilar. For CYP2C19*3, the total functional impact on CYP2C19 could be small if the frequencies of the two null alleles CYP2C19*2 and *3 are combined. Regarding CYP2D6*10, frequency difference over 0.1 is observed only between Japanese and Chinese (0.147). Although environmental factors should be considered for PK/PD differences, we could propose that among Japan, Korea, and China, genetic differences are very small for the analyzed common PK-related gene polymorphisms. On the other hand, AFs of the two HLA alleles important for cutaneous adverse drug reactions are diverse even among Eastern Asians and thus should be taken into account.

Ethnic differences in the metabolism, toxicology and efficacy of three anticancer drugs

INTRODUCTION

Large inter-individual and inter-ethnic differences are observed in efficacies and toxicities of medical drugs. To improve the predictability of these differences, pharmacogenetic information has been applied to clinical situations. Expanding pharmacogenetic information would be a valuable tool to the medical community as well as the patient to fulfill the promise of personalized anticancer drug therapy.

AREAS COVERED

This review highlights genetic polymorphisms and ethnic differences of genes, UGT1As, CYP3A4, CES1As, ABCB1, ABCC2, ABCG2, SLCO1B1, CDA and CYP2D6, involved in metabolism and disposition of three anticancer drugs: irinotecan, gemcitabine and tamoxifen.

EXPERT OPINION

Recent pharmacogenetic studies have successfully identified distinct ethnic differences in genetic polymorphisms that are potentially involved in efficacies and toxicities of anticancer drugs. This achievement has led to personalized irinotecan therapy, reflecting ethnic differences in UGT1A1 genotypes, and possible benefits of genetic testing have also been suggested for gemcitabine and tamoxifen therapy, which still requires further validation. The ultimate goal for patients is a high rate or even perfect prediction of efficacies and toxicities of anticancer drugs in each ethnic population. For this challenge, more clinical studies combined with comprehensive omics approaches are necessary to further advance the field.

Incidence of atazanavir-associated hyperbilirubinemia in Korean HIV patients: 30 months follow-up results in a population with low UDP-glucuronosyltransferase1A1*28 allele frequency

Hyperbilirubinemia is frequently observed in Caucasian HIV patients treated with atazanavir. UDP-glucuronosyltransferase 1A1 polymorphism, UGT1A1*28, which is associated with atazanavir-induced hyperbilirubinemia, is less common in Asians than in Caucasians. However, little is known about the incidence of atazanavir-associated hyperbilirubinemia in Asian populations. Our objective was to investigate the incidence of and tolerability of atazanavir-associated hyperbilirubinemia in Korean HIV patients. The prevalence and cumulative incidence of atazanavir-associated hyperbilirubinemia and UGT1A1*28 allele frequency was investigated in 190 Korean HIV-infected patients treated with atazanavir 400 mg per day. The UGT1A1*28 were examined by direct sequencing of DNA from peripheral whole blood. The UGT1A1*28 allele frequency was 11%. The cumulative incidence of any grade of hyperbilirubinemia was 77%, 89%, 98%, and 100%, at 3, 12, 24, and 30 months, respectively. The cumulative incidence of severe (grade 3-4) hyperbilirubinemia was 21%, 41%, 66%, and 75%, at 3, 12, 24, and 30 months, respectively. However, the point prevalence of severe hyperbilirubinemia did not increase with time and remained around 25%. Our data suggest that atazanavir-associated hyperbilirubinemia is common but transient in a population with low UGT1A1*28 allele frequency.

An overview of the recent progress in irinotecan pharmacogenetics

Recent developments in a number of molecular profiling technologies, including genomic/genetic testing, proteomic profiling and metabolomic analysis have allowed the development of 'personalized medicine'. Irinotecan is one of the models for personalized medicine based on pharmacogenetics, and a number of clinical studies have revealed significant associations between UGT1A1*28 and irinotecan toxicity. Based on this cumulative evidence, the US FDA and pharmaceutical companies revised the irinotecan label in June 2005. However, a recommended strategy for irinotecan-dose adjustments based on individual genetic factors has not yet been fully established. This article provides an overview of recent progress in irinotecan pharmacogenetics and discusses the clinical significance of the UGT1A1 genotype/haplotype with regard to severe irinotecan toxicity.

Gene polymorphisms and their role in epilepsy treatment and prognosis

The human genome carries an enormous number of genetic variants, many of them of functional consequence. In epilepsy, they are likely to be involved in drug-specific treatment efficacy, unwanted or even toxic drug reactions, teratogenic risks in pregnancy as well as in the long-term prognosis of patients with epilepsy. As in many other disorders with a complex genetic background, the associated genetic variants that could be verified successfully in replication studies are still only a few. However, new techniques and improved research strategies are likely to increase their number in the foreseeable future, although at a much slower pace as initially expected.

Exploring the genetic architecture of neonatal hyperbilirubinemia

The potential for genetic variation to modulate neonatal hyperbilirubinemia risk is increasingly being recognized. In particular, polymorphisms across three genes involved in bilirubin production and metabolism [glucose-6-phosphate dehydrogenase (G6PD), uridine diphosphate glucuronosyl transferase 1A1 (UGT1A1), and solute carrier organic anion transporter polypeptide 1B1 (SLCO1B1)] may interact with each other and/or environmental contributors to produce significant hyperbilirubinemia. Variant gene co-expression including compound and synergistic heterozygosity enhances hyperbilirubinemia risk, contributing to the etiologic heterogeneity and complex nature of neonatal jaundice.

Pharmacogenetics of irinotecan: An ethnicity-based prediction of irinotecan adverse events

Irinotecan is now regarded as the most active drug for the treatment of colorectal cancer. However, one of the most difficult issues oncologists face is deciding the optimal dose for an individual patient, as each individual shows different outcomes even at the same dose with regard to treatment related adverse events, ranging from no toxicity to a lethal event. Inherited genetic polymorphism of a single gene or multiple genes (haplotype or linkage disequilibrium) involved in SN-38 glucuronidation, a predominant route of irinotecan detoxification, is now recognized as a significant factor that can alter the incidence of side effects. Attempts to explore such inherited genetic variability have been focused on elucidating interindividual as well as interethnic differences. Genotyping studies in relation to adverse events in an individual or in a group of similar ethnicity should contribute to establishing individual-oriented or ethnicity-oriented irinotecan treatment regimens. This review highlights current single- or multi-tired approaches for the elucidation of genetic predispositions of patients to severe toxicities, especially among Asians. The purpose of this is to contribute to minimizing toxicity by dose modifications, with the consequent aim of maximizing dose intensity and efficacy, an ultimate goal of irinotecan-individualized therapy.

Haplotypes in the UGT1A1 gene and their role as genetic determinants of bilirubin concentration in healthy German volunteers

BACKGROUND

Genetic variations of UDP-glucuronyltransferase 1A1 (UGT1A1) influence the concentration of serum bilirubin. We investigated the association of four common polymorphisms including UGT1A1-53(TA)(n), and common haplotypes of the UGT1A1 gene with bilirubin levels in 218 Caucasian volunteers.

METHODS

Total bilirubin was measured in serum of 218 healthy Caucasian volunteers. Genotyping of four genetic variants was performed: UGT1A1-53(TA)(6/7), UGT1A1c.-3279T>G, UGT1A1c.-3156G>A, and UGT1A1c.211G>A. The association between polymorphisms/haplotypes and bilirubin levels were determined.

RESULTS

Minor allele frequencies were 0.36 for UGT1A1-53(TA)(7), 0.47 for c.-3279G, 0.33 for c.-3156A and 0.006 for c.211A. The three promoter polymorphisms were in close linkage disequilibrium. Common haplotypes were: -53(TA)(6)/c.-3279T/c.211G (frequency 0.530), -53(TA)(7)/c.-3279G/c.211G (frequency 0.365), and -53(TA)(6)/c.-3279G/c.211G (frequency 0.099). Male sex, UGT1A1-53(TA)(6/7) and the c.-3279GG variant were significantly associated with higher bilirubin concentrations.

CONCLUSIONS

Two UGT1A1 promoter polymorphisms (-53(TA)(6/7) and c.-3279T>G) and a common haplotype of the UGT1A1 gene are associated with serum bilirubin concentrations in Caucasians.

Role of UGT1A1*6 in irinogenetics in Asians

Evaluation of: Jada SR, Lim R, Wong CI et al.: Role ofUGT1A1*6, UGT1A1*28 and ABCG2 c.421C>A polymorphisms in irinotecan-induced neutropenia in Asian cancer patients. Cancer Sci. 98(9), 1461-1467 (2007). The pharmacokinetics and toxicity of irinotecan vary widely among patients. This review focuses primarily on a study of the role of UGT1A1*6, UGT1A1*28, and ABCG2 421C>A in three Asian cancer patient populations treated with a 3-weekly regimen of irinotecan. In that study, a statistically significantly higher level of SN-38 and a relatively lower degree of glucuronidation occurred in patients with the UGT1A1*6 homozygote genotype than in patients with the reference genotype. The UGT1A1*6 allele was associated with an increased risk of severe neutropenia. In addition, the study of gene allele frequencies in three healthy Asian populations indicated that the allelic frequency of UGT1A1*6 was higher in the healthy Chinese subjects than in the Malaysian or Indian subjects. UGT1A1*28 and ABCG2 421C>A were not associated with the pharmacokinetics of SN-38 or the severity of neutropenia. In this evaluation, we put this study into the context of similar studies of irinogenetics (irinotecan pharmacogenetics) in Asians and discuss the application of UGT1A1 testing in Asian cancer patients treated with irinotecan-containing regimens.

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.

Pharmacogenetics of irinotecan: clinical perspectives on the utility of genotyping

Depending upon the UDP glucuronosyltransferase 1A1 (UGT1A1) genotype, patients are more or less susceptible to the risk of severe toxicity of irinotecan. As the US FDA-approved label of irinotecan (CPT-11, Camptosar®) has been recently revised to include UGT1A1 genotype among potential risk factors for toxicity, it is expected that UGT1A1 genotyping will be increasingly used in patients undergoing irinotecan treatment. At present, the label states that *28/*28 (7/7) genotype patients are at higher risk of neutropenia and should be treated at a lower dose of irinotecan. Although effective alternative drugs (i.e., oxaliplatin) exist for metastatic colorectal cancer (the main indication of irinotecan), recent studies have confirmed that irinotecan has an important place in the management of this disease. We feel that now is the time for addressing questions around the UGT1A1*28 testing that many oncologists might have had but remained unanswered. For example, does the test have adequate sensitivity/specificity? Can the test results be effectively utilized to guide therapy of metastatic colorectal cancer patients? Is it possible that the *1/*1 (6/6) patients are underdosed? How can the genetic prediction of irinotecan toxicity be improved? Is the UGT1A1*28 test fully predictive of the UGT1A1 deficiency in patients who are not of Caucasian origin? Clinicians and investigators interested in a discussion of each of these points could find this article a useful source.

Intra-ethnic differences in genetic variants of the UGT-glucuronosyltransferase 1A1 gene in Chinese populations

Variants within the human UGT1A1 gene are associated with irinotecan induced severely adverse reactions and hyperbilirubinemia. Intra-ethnic differences in the genetic variation and haplotypes of UGT1A1 gene have been analyzed in the present study. Relationship between the concentrations of total serum bilirubin (T-bil) and haplotype structure of UGT1A1 in healthy people were also evaluated. We genotyped five functional polymorphisms including -3279T>G and -3156G>A in the enhancer region, (TA)6>7 in the TATA box, and 211G>A (G71R), 686C>A (P229Q) in the exon1 region of UGT1A1 in three groups of healthy Chinese ethnic populations, consisting of 264 subjects of She origin, 539 of Han origin and 273 of Dong origin. The distribution of -3279T>G, (TA)6>7, 211G>A of UGT1A1 differed greatly as between the three ethnic groups. All of six haplotypes differed considerably between at least two of the three groups, which highlighted the need to analyze clinically irinotecan toxicity relevant SNPs and haplotypes in a variety of different racial groups within the Chinese population. Total bilirubin concentration in homozygous carriers of the -3279G and (TA)7 allele were significantly higher than those in heterozygous carriers or homozygous carriers of wild-type alleles. Carriers of the variant haplotypes (-3279G; -3156A; (TA)7; 211G; 686C) had higher serum T-Bil concentrations compared with the other groups. Our results indicate that heterogeneity among different ethnic populations is possibly the result of microevolution and is relevant to studies into the effect of tailored drug treatment.

Study of the genetic determinants of UGT1A1 inducibility by phenobarbital in cultured human hepatocytes

UGT1A1 is induced by phenobarbital. We investigated whether three common UGT1A1 variants are associated with the variability in UGT1A1 inducibility. Human hepatocytes were incubated with 2 mM phenobarbital for 2 and 6 days followed by 5 microM SN-38 (1 h), a UGT1A1 probe. SN-38 glucuronidation in the cell media was measured by high-performance liquid chromatography. Three UGT1A1 promoter variants [-53(TA)(6>7), -3156G > A and -3279T > G] were genotyped. Significant induction of UGT1A1 catalytic activity was observed in 82% and 100% of the cultures treated with phenobarbital for 2 days (median fold-induction = 1.6, range 1.3-2.8; n = 28) and 6 days (median fold-induction = 2.8, range 1.6-6.4; n = 16), respectively. After 2 days of treatment, a negative correlation was observed between the UGT1A1 basal activities and the fold-induction (Spearman r = -0.52, P < 0.005). By contrast, the UGT1A1 activities in the basal and induced states were highly correlated (Spearman r = 0.95, P < 0.0001). Similar results were observed after 6 days of treatment. The allele frequencies were not significantly different between induced (n = 22) and non-induced preparations (n = 6) (P > 0.05). The fold-induction was not associated with any variants (P > 0.05). The basal and induced activities were correlated with -53(TA)(6>7) (and with -3156G > A due to almost complete linkage with the -53 indel) (P = 0.001). No association was found with the -3279T > G single nucleotide polymorphism (P > 0.05). The indel at -53 affects the basal phenotype and appears to limit the hepatocyte capability of maximal induction after phenobarbital. However, variants at -53, -3156 and -3279 are not associated with variability in UGT1A1 inducibility.

Comparative genomics analysis of human sequence variation in the UGT1A gene cluster

Common polymorphisms within the human UGT1A gene locus are associated with irinotecan and tranilast toxicity. To uncover additional functional variation across this gene cluster, cross-species sequence comparisons were performed. Evolutionarily conserved segments (a total of 47.1 kb) were re-sequenced in 24 African-American, 24 European-American, and 24 Asian individuals, and 381 segregating sites (including 123 singletons) were identified. Highly conserved coding sites were less likely to be polymorphic than diverged sites (P<0.0001) but this pattern was not observed at non-coding sites (P=0.1025). Among coding variants, the distribution of those computationally predicted to affect function was skewed toward low frequencies. Some alleles occurred at similar frequencies in each population; others had wide disparities. Although strong linkage disequilibrium was detected among the hepatically expressed genes, the degree of linkage disequilibrium varied among populations. These results suggest that rare functional gene variants and inter-population variability must be considered in the interpretation of association studies between UGT1A and drug metabolism/toxicity phenotypes.

Sequence diversity and haplotype structure at the human CYP3A cluster

The four members of the human CYP3A subfamily play important roles in the clearance of xenobiotics, hormones, and environmental compounds. Many SNPs at the CYP3A locus have been characterized, with several showing large allele frequency differences across populations. In addition to the effects of CYP3A SNPs on drug metabolism, recent studies have highlighted the potential for CYP3A variation in susceptibility to several common phenotypes, including hypertension and cancer. We previously showed that the CYP3A4 and CYP3A5 genes have a strong haplotype structure at varying frequencies across ethnic groups. Here, we extend our re-sequencing survey to the remaining CYP3A genes in the same cluster, CYP3A7 and CYP3A43. Our study identified a large number of SNPs in coding and conserved noncoding sequences, several of which are common. The combined data set allows us to investigate patterns of sequence variation and linkage disequilibrium at the entire CYP3A locus for use in future association studies.

Haplotypes of variants in the UDP-glucuronosyltransferase1A9 and 1A1 genes

OBJECTIVES

Nine different functional UGT1A enzymes are generated from a single UGT1A gene by alternative splicing, with each enzyme having a unique exon 1. SN-38, the active metabolite of the anticancer agent irinotecan, is metabolized by both UGT1A1 and UGT1A9. We aim to characterize the UGT1A9-UGT1A1 haplotypes in Asians and Caucasians and gain insights on their functional consequences.

METHODS

Asian and Caucasian individuals were genotyped for UGT1A1 and UGT1A9 variants.

RESULTS

A higher frequency of the UGT1A9 -118T10 allele was observed in Asians compared to Caucasians, while the -275T>A and -2152C>T variants were relatively uncommon in Caucasians and not found in Asians. The strongest linkage disequilibrium (LD) was observed between the UGT1A1 -53 and -3156 and between the UGT1A9 -275 and -2152 loci. Lower LD was observed between the -118 UGT1A9 variant and the UGT1A1 variants. Fourteen UGT1A9-UGT1A1 haplotypes were found in Asians, seven of them found to be shared by both populations. Common UGT1A9-UGT1A1 diplotypes were defined, and a difference was observed across the SN-38 glucuronidation rates in Caucasian livers stratified by diplotypes.

CONCLUSION

This study for the first time described common UGT1A9-UGT1A1 haplotypes, highlighting important ethnic differences between Asians and Caucasians. If the functional effect of these haplotypes can be confirmed, this haplotypic information would be applicable to the correct design of prospective clinical studies of irinotecan, as well as of other drugs primarily metabolized by both UGT1A1 and UGT1A9.

Racial variability in haplotype frequencies of UGT1A1 and glucuronidation activity of a novel single nucleotide polymorphism 686C> T (P229L) found in an African-American

Ethnic differences in genetic polymorphisms in UDP-glucuronosyltransferase 1A1 (UGT1A1) were investigated among African-Americans, Caucasians, and Japanese using samples obtained from 150 individuals for each population. Genotyping of -3279T>G in the phenobarbital-responsive enhancer module, TA repeats in the TATA box, 211G>A (G71R) and 686C>A (P229Q) in exon 1, and three single nucleotide polymorphisms (SNPs) (1813C> T, 1941C>G, and 2042C>G) in the 3'-untranslated region in exon 5 was performed. Eight haplotypes of block 1 (exon 1 and its 5'-flanking region) harboring the first four variations were assigned to each individual. The dominant haplotype for African-Americans was *28b (-3279G;TA(7); 211G;686C) (0.446), whereas that for the Japanese was *1a (-3279T; TA(6);211G;686C) (0.610). Frequencies of the two haplotypes *1a and *28b were comparable in Caucasians. Haplotype *6a (-3279T;TA(6); 211A;686C) was characteristic of the Japanese, whereas haplotypes *36b and *37b (-3279T;TA(5) and TA(8);211G;686C) were found mostly in African-Americans. Although the three SNPs in block 2 (exons 2-5) were in complete linkage in the Japanese, they were not completely linked in African-Americans or Caucasians. These differences in haplotype distribution patterns among the three populations suggest the possibility of ethnic differences in toxicity profiles of drugs detoxicated by UGT1A1. A novel SNP, 686C>T (P229L), was found in an African-American. The intrinsic clearance of 7-ethyl-10-hydroxycamptothecin (SN-38) by P229L UGT1A1 expressed in COS-1 cells was about 3% of the wild type. The results of Western blotting and real-time reverse transcription-polymerase chain reaction suggest that the low glucuronidation activity of the variant was partly due to its low stability. The variation 686C>T may cause high toxicity during 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT-11) therapy or hyperbilirubinemia in patients.