Variations in the UDP-glucuronosyltransferase 1A1 gene for the development of unconjugated hyperbilirubinemia in Taiwanese

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.

Effect of UDP-glucuronosyltransferase 1A1 activity on risk for developing Gilbert's syndrome

Variations at the six nucleotides -3279 (T > G), -53 (A[TA]₆ TAA > A[TA]₇ TAA), 211 (G > A), 686 (C > A), 1091 (C > T), and 1456 (T > G) in the UDP-glucuronosyltransferase 1A1 (UGT1A1) gene were determined in 178 Taiwanese patients with Gilbert's syndrome and in 200 healthy adults. Every subject was classified as a genotype depending on variation status of the six nucleotides in the UGT1A1 gene. The UGT1A1 activity for each genotype was calculated and then those genotypes were divided into 10 subgroups (Q1~Q10) according to their UGT1A1 activities, by using 10% as an interval. There were 24 genotypes observed, with UGT1A1 activity ranged 9%~100% of normal. There were two and six subjects with Gilbert's syndrome and none of healthy controls carrying genotypes in the Q1 and Q2 subgroups, respectively. The odds of developing Gilbert's syndrome were significantly higher for subjects carrying genotypes in the Q3, Q4, and Q5 subgroups than for those with genotype in the Q10 subgroup (odds ratios: 240.22, 59.80, and 14.67, respectively, P < .001 for each). Among the 178 patients of Gilbert's syndrome, serum bilirubin value was inversely correlated with UGT1A1 activity (r = -.306, P < .001). The sensitivity was 72.0% and the specificity was 90.5% by using UGT1A1 activity ≦40% of normal as the cut-off point to distinguish between healthy subjects and patients of Gilbert's syndrome. Our results demonstrate that UGT1A1 activity is certainly a determinate for serum bilirubin value and UGT1A1 activity ≦40% of normal is a proper risk factor for the development of Gilbert's syndrome.

The impact of the UGT1A1*60 allele on bilirubin serum concentrations

AIM

Identify the functional status of the uridine-diphosphate glucuronyl transferase 1A1 (UGT1A1) -3279T>G (*60) variant.

MATERIALS & METHODS

Retrospective review of clinically obtained serum bilirubin concentrations in pediatric patients to evaluate the association of the UGT1A1 -3279T>G (*60) variant with bilirubin concentrations and assessed linkage disequilibrium of the UGT1A1 -3279T>G (*60) and A(TA)7TAA (*28) variants.

RESULTS

Total bilirubin concentration did not differ between patients who had a UGT1A1*1/*1 diplotype and patients homozygous for the UGT1A1 -3279T>G (*60/*60) variant. Total bilirubin concentration was lower in patients homozygous for the UGT1A1 -3279T>G (*60/*60) variant than in patients homozygous for the UGT1A1 A(TA)7TAA (*28/*28) variant (p < 0.01). The -3279T>G (*60) and A(TA)7TAA (*28) variants were in strong incomplete linkage disequilibrium in both black and white patients.

CONCLUSION

The presence of the UGT1A1 -3279T>G (*60) variant is not associated with increased bilirubin concentrations.

Prolonged Hyperbilirubinemia in a Neonate with a Novel Mutation in the UDP-glucuronosyltransferase 1A1 Gene

The total bilirubin value of a male infant was 385 μmol/l on day 5. Liver function test results were normal and there was no evidence of sepsis and no hemolysis reaction. Phototherapy was administered and on day 8 the patient's total bilirubin level was 255 μmol/l. Intermittent episodes of hyperbilirubinemia occurred without phototherapy, with the total bilirubin level reaching 335 μmol/l on day 19. A 3-day regimen of phenobarbital was administered and on day 24 his total bilirubin level was 180 μmol/l. The patient was discharged. At the age of 2 months, the total bilirubin value was 27 μmol/l. His direct bilirubin value was <15% of total bilirubin in every determination. A family study of the UDP-glucuronosyltransferase(UGT)1A1 gene showed that the infant carries a homozygous mutation at nucleotide -3279 plus compound heterozygous mutations at nucleotides 782 and 1091. The mutation at nucleotide 782 is a novel finding. Gilbert's syndrome was diagnosed.

UGT1A1 gene variants and clinical risk factors modulate hyperbilirubinemia risk in newborns

OBJECTIVE

To study the contribution of UGT1A1 gene variants and clinical risk factors in modulating hyperbilirubinemia risk in newborns.

STUDY DESIGN

Seven UGT1A1 gene variants and clinical risk factors were studied in 113 hyperbilirubinemia cases and 218 control newborns. Hyperbilirubinemia was defined as the total serum bilirubin levels >95th percentile of the American Academy of Pediatrics nomogram. The study population included term (37 to 41 weeks) newborns below 2 weeks of age.

RESULT

UGT1A1 gene variants, namely, c.211G>A, g.-3279T>G, TATA box polymorphism and CAT insertion were identified as independent molecular risk factors for neonatal hyperbilirubinemia, whereas c.686C>A, c.1091C>T and c.1456T>G were not detected in study cohort. Among clinical risk factors, excessive weight loss, sepsis and ABO incompatibility emerged as independent risk factors. Co-expression of UGT1A1 variants and clinical risk factors further accentuated the risk of neonatal hyperbilirubinemia.

CONCLUSION

Multiple risk factors, whether genetic or clinical, are instrumental in modulating hyperbilirubinemia risk in newborns. Disordered bilirubin conjugation through interactions of UG1TA1 gene variants contributes to the clinical phenotype of neonatal hyperbilirubinemia.

Heme oxygenase-1 gene variants and hyperbilirubinemia risk in North Indian newborns

Heme oxygenase-1 (HO-1) is a rate-limiting enzyme in bilirubin metabolism, and its genetic variant may modulate hyperbilirubinemia risk in neonates. The aim of the present study was to assess the association between heme oxygenase-1 gene variants and hyperbilirubinemia risk in Indian newborns. In a prospective case-control study, we analyzed (GT)n repeats and g.-413A>T variant of HO-1 gene and UGT1A1 gene variants in 100 case newborns with total serum bilirubin (TSB) levels exceeding 95th percentile and 100 control newborns with TSB levels below 75th percentile on the hour-specific bilirubin nomogram of the American Academy of Pediatrics. Study population consisted of term (37-41 weeks) and late preterm (34-36 weeks) newborns during the first 2 weeks of age. In our analysis, the (GT)n allele was highly polymorphic, ranging in number from 15 to 40. The incidence of short (GT)n allele (≤ 20) was significantly higher in neonates with hyperbilirubinemia than in controls. Although g.-413A>T variant was widely prevalent in the study population, no difference was noted in its prevalence between cases and controls. Short (GT)n repeats of HO-1 gene, c.211G>A variant of UGT1A1 gene, and excessive weight loss were independent risk factors for neonatal hyperbilirubinemia. In the presence of two or more risk factors, the odds of developing neonatal hyperbilirubinemia were high. Shorter (GT)n genotype in the promoter region of HO-1 gene is significantly associated with hyperbilirubinemia risk in Indian newborns. This genotype may interact with other genetic and clinical risk factors to further potentiate hyperbilirubinemia risk in newborns.

Short communication: lack of correlation between UGT1A1*6, *28 genotypes, and plasma raltegravir concentrations in Japanese HIV type 1-infected patients

Raltegravir is metabolized by glucuronidation via UDP-glucuronosyltransferase 1A1 (UGT1A1). We analyzed the genotypes of UGT1A1 (*6, *27, and *28) and their contribution to plasma raltegravir concentrations in 56 Japanese HIV-1-infected patients in the National Hospital Organization Nagoya Medical Center of Japan. Among the 56 patients, the UGT1A1 genotype in two patients was *6 homozygote. Heterozygous variants were found in 13 patients for *6 and in 11 patients for *28, while all of the patients were found to carry wild-type sequences at the position corresponding to the *27 allele. Plasma raltegravir concentration of a male patient with *6 homozygote (0.53 μg/ml) was modestly higher than that of patients with wild type (0.12 μg/ml) or *6 heterozygote (0.16 μg/ml). Another female patient with the *6 homozygote had a low plasma raltegravir concentration (0.03 μg/ml). Patients heterozygous for the *6 or *28 allele did not display significantly different plasma raltegravir concentrations compared to patients homozygous for the respective wild-type allele. Thus, in the present study, we showed that heterozygous reduced-function *6 and *28 alleles appear to have no significant effect on plasma raltegravir concentrations in Japanese HIV-1-infected patients. However, variability in raltegravir concentration and small patient population precluded a correlation between UGT1A1*6 homozygosity and plasma raltegravir concentration. To clarify the contribution of UGT1A1*6 or *28 polymorphisms to plasma raltegravir concentrations, further investigations on larger subject populations are required.

Combined effect of regulatory polymorphisms on transcription of UGT1A1 as a cause of Gilbert syndrome

Background

Gilbert syndrome is caused by defects in bilirubin UDP-glucuronosyltransferase (UGT1A1). The most common variation believed to be involved is A(TA)7TAA. Although several polymorphisms have been found to link with A(TA)7TAA, the combined effect of regulatory polymorphisms in the development of Gilbert syndrome remains unclear.

Methods

In an analysis of 15 patients and 60 normal subjects, we detected 14 polymorphisms and nine haplotypes in the regulatory region. We classified the 4-kbp regulatory region of the patients into: the TATA box including A(TA)7TAA; a phenobarbital responsive enhancer module including c.-3275T>G; and a region including other ten linked polymorphisms. The effect on transcription of these polymorphisms was studied.

Results

All haplotypes with A(TA)7TAA had c.-3275T>G and additional polymorphisms. In an in-vitro expression study of the 4-kbp regulatory region, A(TA)7TAA alone did not significantly reduce transcription. In contrast, c.-3275T>G reduced transcription to 69% of that of wild type, and the linked polymorphisms reduced transcription to 88% of wild type. Transcription of the typical regulatory region of the patients was 56% of wild type. Co-expression of constitutive androstane receptor (CAR) increased the transcription of wild type by a factor of 4.3. Each polymorphism by itself did not reduce transcription to the level of the patients, however, even in the presence of CAR.

Conclusions

These results imply that co-operation of A(TA)7TAA, c.-3275T>G and the linked polymorphisms is necessary in causing Gilbert syndrome.

Uridine diphosphate glucuronosyl transferase 1A1 promoter polymorphism is associated with choledocholithiasis in Taiwanese patients

BACKGROUND AND AIMS

The gene product of the uridine diphosphate glucuronosyl transferase 1A1 (UGT1A1) is crucial to bilirubin metabolism. Mutations in this gene subsequently result in disease presented with unconjugated hyperbilirubinemia. A previous study showed that a TA-repeat polymorphism in the promoter region of this gene might play a role in the metabolism of bilirubin. Whether this polymorphism might predispose choledocholithiasis is unclear.

METHODS

We recruited 32 patients who were diagnosed with pigment choledocholithiasis (common bile duct stones) by endoscopic retrograde cholangiopancreatography (ERCP) morphology and 107 population controls. The TA-repeat in the UGT1A1 promoter was genotyped.

RESULTS

We found that among the 32 patients, 15 (46.9%) were wild type (A[TA](6)TAA homozygous); 15 (46.9%) were a heterozygous variation (A[TA[(6)TAA/A[TA](7)TAA) and 2 (6.2%) were a homozygous variation (A[TA](7)TAA). Among the controls, 81 (75.7%) were wild type, 23 (21.5%) were a heterozygous variation and 3 (2.8%) were a homozygous variation. The genotype distribution was significantly different between patients and controls.

CONCLUSIONS

The results suggest that the UGT1A1 promoter TA-repeat polymorphism is associated with choledocholithiasis in Taiwanese patients.

Genetic polymorphisms in the TATA box and upstream phenobarbital-responsive enhancer module of the UGT1A1 promoter have combined effects on UDP-glucuronosyltransferase 1A1 transcription mediated by constitutive androstane receptor, pregnane X receptor, or glucocorticoid receptor in human liver

Transcription of UDP-glucuronosyltransferase (UGT) 1A1 is regulated by the transcription factors, constitutive androstane receptor (CAR), pregnane X receptor (PXR), glucocorticoid receptor (GR), hepatocyte nuclear factor (HNF) 1 alpha, and HNF4 alpha. The purpose of this study was to determine whether the genetic polymorphisms in the RNA polymerase II core promoter and the upstream phenobarbital-responsive element module (PBREM) of the UGT1A1 promoter have combined effects on UGT1A1 transcription mediated by the transcription factors. A polymorphism of A(TA)(5-8)TAA in the UGT1A1 TATA box and a single nucleotide polymorphism of -3279T>G in PBREM were genotyped in 98 human liver samples. Relative mRNA levels of CAR, PXR, GR, HNF1 alpha, HNF4 alpha, and UGT1A1 were quantified by a multiplex branched DNA technique. Correlations of mRNA levels between UGT1A1 and the transcription factors were established in liver samples with different combined genetic polymorphisms. Correlation of mRNA levels between UGT1A1 and CAR, PXR, or GR, but not HNF1 alpha or HNF4 alpha, was abolished in the samples with the combined genotype of TA7/7 plus -3279G/G, which was also associated with significantly lower UGT1A1 mRNA levels compared with other combined genotypes. Correlations of mRNA levels between UGT1A1 and CAR or PXR were reduced but not abolished in the samples with the combined genotype of TA6/7 plus -3279 G/G, which showed significantly lower UGT1A1 mRNA levels compared with the combined genotype of TA6/7 plus -3279T/G and other genotypes containing TA6/6. In conclusion, the combined genotypes containing A(TA)(7)TAA and -3279G decrease UGT1A transcription mediated by CAR, PXR, or GR but not by HNF1 alpha or HNF4 alpha.