Number Of TA Repeats Research Articles

Irinotecan and uridine diphosphate glucuronosyltransferase 1A1 pharmacogenetics

Pharmacogenetic research indicates a relationship between a polymorphism in the gene encoding uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) and irinotecan inactivation, in that degradation of SN-38, the active metabolite of irinotecan, correlates inversely with the number of TA repeats in the TATA element of the UGT1A1 promoter region. Individuals who are homozygous for the UGT1A1*28 allele (7 repeats) may exhibit reduced degradation of SN-38 and increased probability of severe toxicities. Clinical study results, as reported in the literature, have not been uniform, however, in showing a relation between genotype and the development of toxicities. Even when correlations are statistically significant, confidence intervals are wide, rendering assessment of individual risk difficult at best. Irinotecan labeling recommends testing for the UGT1A1*28 allele and reducing irinotecan dosing in patients who are positive to reduce the likelihood of dose-limiting neutropenia only, but not diarrhea. Importantly, both dose-limiting neutropenia and diarrhea are dependent on numerous known and unknown factors, such as the specific regimen used, duration of therapy, doses, cycle of treatment, and complexities of irinotecan pharmacodynamics and pharmacokinetics, including other key enzymes and drug transporters. Guidance on how to modify irinotecan dosing or how to incorporate the impact of multiple variables into clinical decision-making does not exist. Furthermore, pharmacogenomic test results at this time can only provide an estimate of risk for subsets of populations rather than a risk-benefit estimate for an individual. Consequently, these test results are supplementary to clinical judgment, which requires assessing multiple variables that contribute to phenotype to arrive at individual dosing decisions.

Association between the UGT1A1 TA-Repeat Polymorphism and Bilirubin Concentration in Patients with Intermittent Claudication: Results from the CAVASIC Study

Bilirubin has antioxidative and cytoprotective properties. Low plasma concentrations of bilirubin are reportedly associated with the development of coronary and cerebrovascular disease, and bilirubin concentrations are strongly correlated with the enzyme activity of the hepatic uridine diphosphate glucuronosyltransferase (UGT1A1). The activity of UGT1A1 is influenced by a TA-repeat polymorphism in the promoter of the UGT1A1 gene (UDP glucuronosyltransferase 1 family, polypeptide A1). In a case-control study, we investigated the association between the UGT1A1 polymorphism, bilirubin concentration, and intermittent claudication. We included 255 consecutive male patients presenting with intermittent claudication in the investigation and matched the patients by age and diabetes mellitus with 255 control individuals. Plasma bilirubin concentrations were significantly lower in patients than in controls [mean (SD), 12.5 (5.3) micromol/L vs 15.4 (7.9) micromol/L; P < 0.001]. We found a clear association between the number of TA repeats and plasma bilirubin concentration. Considering the 6/6 TA-repeat genotype as the wild type, we observed a slight increase in bilirubin concentration individuals with the heterozygous 6/7 genotype and pronounced increases for those with the homozygous 7/7 genotype. This association occurred in both controls and patients; however, patients and controls were not significantly different with respect to UGT1A1 TA-repeat genotype frequencies. Our study of a well-phenotyped group of patients with intermittent claudication and control individuals revealed a clear association between low bilirubin concentrations and peripheral arterial disease but no association between the UGT1A1 polymorphism and the disease.

Facteurs génétiques déterminant les variations anatomiques de la prostate

The determinants of macroscopic and microscopic anatomical variants of the prostate during ageing are poorly defined. The authors evaluated the correlation between specific gene polymorphisms involved in androgen and oestrogen synthesis and gross (prostatic weight) and microscopic anatomy (stroma/epithelium ratio) of the prostate during ageing.The prostatic weight and stromal surface area of an autopsy series of 85 men over the age of 50 were measured, then compared as a function of gene polymorphisms involved in androgen or oestrogen regulation. The following polymorphisms were studied: number of CAG repeats of the androgen receptor (AR), number of TA repeats and the V89L variant of the 5-alpha-reductase gene (SRD5A2) for androgens, and the A1A2 variant of 17-alpha-hydroxylase (CYP17) and number of TTTA repeats of the aromatase (CYP19) for oestrogens.No correlation was observed between the number of TA repeats of the SRD5A2 gene or TTTA repeats of the CYP19 gene and anatomical parameters of the prostate. A statistically significant positive correlation was observed between age and prostate weight (r=0.21, p=0.05) and a statistically significant negative correlation was observed between prostate weight and number of CAG repeats (r=-0.32, p=0.003). The group with less than 20 CAG repeats was associated with a higher prostate weight than the other group. The stromal surface area was greater in the [20-23] CAG repeat group (p=0.02), and in the A2A2 group of CYP17 (p=0.016) than in the other groups.A small number of CAG repeats is associated with a higher prostate weight. The mean number of CAG repeats of the androgen receptor and the A2A2 variant of the CYP17 gene are associated with a larger stromal surface area.

Genetic polymorphisms in uridine diphospho-glucuronosyltransferase 1A1 and breast cancer risk in Africans

The UDP-glucuronosylatransferase 1A1 (UGT1A1) gene is involved in the metabolism of estrogen and detoxification of potential carcinogens. The number of TA repeats in the promoter region of UGT1A1 has been linked to breast cancer risk, but results varied by race. We performed a comprehensive assessment of genetic polymorphisms in the UGT1A1 gene, and examined these polymorphisms and TA repeats in relation to breast cancer risk in a case-control study in Nigeria. 512 breast cancer cases and 226 community controls were genotyped for UGT1A1. Compared with high-activity TA repeat genotypes, the odds ratios (OR) for low-activity and moderate-activity genotypes were 0.47 (95% confidence interval CI, 0.26-0.83) and 0.64 (95% CI, 0.39-1.06), respectively, in premenopausal women (P = 0.009 for trend), but no association was observed in postmenopausal women (P = 0.24). The effect of TA repeats was also differentiated by age: the OR was 0.39 (95% CI 0.21-0.71) for low-activity genotypes and 0.58 (95% CI 0.33-1.00) for moderate-activity genotypes in women <45 years old (P = 0.002 for trend), but no association was observed in women >or=45 years old (P = 0.15). Haplotype analysis showed that UGT1A1 haplotypes were highly diverse with blocked structures. We found a specific haplotype in block 2 that was significantly associated with a 2.1-fold elevated risk (95% CI 1.05-4.39; P = 0.04). In contrast with previous studies, we found low-activity TA repeat alleles were protective against breast cancer among premenopausal indigenous Africans, suggesting that the role of UGT1A1 in breast cancer development may vary by population, presumably due to different environmental and genetic modifier effects.

UGT1A1Promoter Genotype Correlates With SN-38 Pharmacokinetics, but Not Severe Toxicity in Patients Receiving Low-Dose Irinotecan

To study the association between UDP-glucuronosyltransferase 1A1 (UGT1A1) genotypes and severe toxicity as well as irinotecan disposition in pediatric patients with solid tumors receiving low-dose, protracted irinotecan (15 to 75 mg/m2 daily for 5 days for 2 consecutive weeks). Seventy-four patients on five institutional clinical trials received irinotecan (15 to 75 mg/m2) daily intravenously or orally for 5 days for 2 consecutive weeks. Genomic DNA was genotyped for UGT1A1*28, and patients were designated as 6/6, 6/7, or 7/7 depending on the number of TA repeats in the UGT1A1 promoter region. Patients were evaluated for gastrointestinal and hematologic toxicity, as well as baseline and maximal serum bilirubin levels. Toxicity and pharmacokinetic results were evaluated during courses 1 and 2 of irinotecan therapy. The frequencies of 6/6, 6/7, and 7/7 genotypes were 27 (36.5%), 36 (48.6%), and 9 (12.2%) of 74 patients, respectively. Patients with 7/7 genotype had a statistically greater baseline total bilirubin than patients with 6/6 or 6/7 genotype (P = .005). UGT1A1*28 genotype was not associated with grade 3 and 4 neutropenia (P = .21 for course 1; P = .23 for course 2) or diarrhea (P = .176 for course 1; P = .87 for course 2). However, patients with the 7/7 genotype tended to have higher SN-38 area under the plasma time-concentration curve (AUC) values and lower SN-38G/SN-38 AUC ratios. Severe toxicity was not increased in pediatric patients with the 7/7 genotype when treated with a low-dose protracted schedule of irinotecan. Therefore, UGT1A1 genotyping is not a useful prognostic indicator of severe toxicity for patients treated with this irinotecan dosage and schedule.

UGT1A1 promoter genotype correlates with pharmacokinetics but not toxicity in patients receiving protracted irinotecan (IRN)

3078 Background: Recent USFDA recommendations include a dosage adjustment for patients who are homozygous for the UGT1A1*28 allele (i.e., 7 TA repeats in the promoter) due to an increase in neutropenia when those patients receive IRN. However, this recommendation was based upon data from adults treated with high IRN dosage (e.g., 350 mg/m2). This study evaluates the relationship between UGT1A1 promoter genotype and phenotype (i.e., SN-38 glucuronidation and IRN toxicity) in patients treated with low-dose, protracted IRN. Methods: 31 children treated on 2 institutional protocols received low dosage (20 to 60 mg/m2) i.v. IRN daily for 5 days of 2 consecutive weeks. PK sampling and UGT1A1 genotyping were performed during cycle 1. Patients were designated as 6/6, 6/7, or 7/7 depending on the number of TA repeats in the UGT1A1 promoter region. All patients were evaluable for gastrointestinal and hematological toxicity, primarily grades 3 and 4 neutropenia and diarrhea. Results: The frequencies of 6/6, 6/7, and 7/7 genotypes were 9/31 (29%), 15/31 (48%), and 7/31 (23%), respectively. Patients with 7/7 genotype had a statistically greater baseline bilirubin than patients with 6/6 or 6/7 genotype (p&lt;0.03), but the difference was not considered clinically significant. In females, the SN-38:IRN AUC ratio was greater in patients with 7/7 vs. 6/6 or 6/7 genotype (0.15 vs. 0.05 vs. 0.09;p&lt;0.005). Similarly the SN-38G:SN-38 ratio was less in females with 7/7 vs. 6/6 or 6/7 genotype (1.5 vs. 4.1 vs. 3.5;p&lt;0.03). Patients with 7/7 genotype did not have a greater incidence of diarrhea (0/7) or neutropenia (0/7) than patients with 6/6 (3/9 with diarrhea, 2/9 with neutropenia) or 6/7 (3/15 with diarrhea, 1/15 with neutropenia) genotype. Conclusions: Although female patients with a 7/7 genotype did have altered SN-38 disposition, toxicity was not increased in patients with the 7/7 genotype treated with a low dose protracted schedule of irinotecan. Therefore, no dosage adjustment for genotype is indicated with this IRN dosing schedule. No significant financial relationships to disclose.

Irinogenetics: What Is the Right Star?

Irinogenetics: What Is the Right Star?

Estrogen receptor α promoter polymorphism: stronger estrogen action is coupled with lower sperm count

Although the importance of estrogens in male reproduction is indisputable, little attention has been paid to the role of estrogen receptor (ER) gene mutations in male infertility. Significant correlation between (TA)n repeat allelic variants and lumbar bone mineral density was previously observed in the promoter region of the ERalpha gene, indicating that allelic combinations with higher number of (TA)n repeats are functionally more active genetic variants. We studied the (TA)n repeat polymorphism situated in the promoter region of the ERalpha gene in a large group of infertile and normospermic men (n = 347). Although the (TA)n polymorphism failed to show a significant association with male infertility, we found a significant effect of this polymorphism on sperm count. In the group of infertile men, the mean TA repeat number and sperm concentration (P = 0.022) and total sperm number (P = 0.043) were inversely correlated, showing an association between higher TA repeat number (genotype A) and lower sperm production. In line with this observation, normospermic subjects with genotype A had a significantly lower mean sperm concentration with respect to men bearing genotype B with shorter TA alleles (P < 0.05) and a lower total sperm count (P < 0.01). Our data indicate that specific allelic combinations of the ERalpha, which confer a stronger estrogen effect, may negatively influence human spermatogenesis.

Association of oestrogen receptor α gene polymorphisms with postmenopausal bone loss, bone mass, and quantitative ultrasound properties of bone

Background: The gene encoding oestrogen receptor α (ESR1) appears to regulate bone mineral density (BMD) and other determinants of osteoporotic fracture risk. Objective: To investigate the relation between common polymorphisms...

Bilirubin UDP-glucuronosyltransferase 1A1 ( UGT1A1) gene promoter polymorphisms and HPRT, glycophorin A, and micronuclei mutant frequencies in human blood

A dinucleotide repeat polymorphism (5-, 6-, 7-, or 8-TA units) has been identified within the promoter region of UDP-glucuronosyltransferase 1A1 ( UGT1A1) gene. The 7-TA repeat allele has been associated with elevated serum bilirubin levels that cause a mild hyperbilirubinemia (Gilbert’s syndrome). Studies suggest that promoter transcriptional activity of UGT1A1 is inversely related to the number of TA repeats, and that unconjugated bilirubin concentration increases directly with the number of TA repeat elements. Because bilirubin is a known antioxidant, we hypothesized that UGT1A1 repeats associated with higher bilirubin may be protective against oxidative damage. We examined the effect of UGT1A1 genotype on somatic mutant frequency in the hypoxanthine-guanine phosphoribosyl-transferase ( HPRT) gene in human lymphocytes and the glycophorin A (GPA) gene of red blood cells (both N0, NN mutants), and the frequency of lymphocyte micronuclei (both kinetochore (K)-positive or micronuclei K-negative) in 101 healthy smoking and nonsmoking individuals. As hypothesized, genotypes containing 7- and 8-TA displayed marginally lower GPA_NN mutant frequency relative to 5/5, 5/6, 6/6 genotypes ( P<0.05). In contrast, our analysis showed that lower expressing UGT1A1 alleles (7- and 8-TA) were associated with modestly increased HPRT mutation frequency ( P<0.05), while the same low-expression genotypes were not significantly associated with micronuclei frequencies (K-positive or K-negative) when compared to high-expression genotypes (5- and 6-TA). We found weak evidence that UGT1A1 genotypes containing 7- and 8-TA were associated with increased GPA_NØ mutant frequency relative to 5/5, 5/6, 6/6 genotypes ( P<0.05). These data suggest that UGT1A1 genotype may modulate somatic mutation of some types, in some cell lineages, by a mechanism not involving bilirubin antioxidant activity. More detailed studies examining UGT1A1 promoter variation, oxidant/antioxidant balance and genetic damage will be needed.

SULT1A1 and UGT1A1 polymorphisms are associated with breast cancer phenotypes in women

Estrogens are an important factor in the development and treatment of breast cancer. SULT1A1 and UGT1A1 metabolize estrogen agonists and antagonists and thus may influence breast cancer risk and treatment. SULT1A1 and UGT1A1 are genetically polymorphic. A common SULT1A1 allele is defined by a His213Arg amino acid substitution (*2) and results in an enzyme with low activity. A common UGT1A1 polymorphism is defined by TA repeats (5,6,7 or 8) in the promoter TATA-box. Transcriptional activity of the promoter is inversely proportional to the number of TA repeats. We hypothesized that individuals with variant capacity to metabolize estrogen agonists and antagonists would exhibit different tumor phenotypes. We performed a case-series study in a cohort of 190 Caucasian women with breast cancer. SULT1A1 and UGT1A1 genotypes were determined using Pyrosequencing and Genescan techniques, respectively, and genotype-phenotype associations were analyzed. We found that SULT1A1*1/*1 genotype was associated with a tumor size <2 cm (OR=2.5, P=0.03). UGT1A1 genotypes containing only low activity alleles (*28/*28, *34/*34 or *28/*34) were associated with late (≥60 years) age of onset (OR=3.2, P=0.049) and DCIS (OR=5.7, P=0.02). Presence of UGT1A1*28 or/and *34 was associated with tumor size ≤4 cm (OR=0.1, P=0.004). In summary, genetic polymorphisms affecting the sulfation and glucuronidation of estrogen agonists and antagonists appear to be associated with specific tumor characteristics. Clinical Pharmacology & Therapeutics (2004) 75, P1–P1; doi: 10.1016/j.clpt.2003.11.004

Estrogen receptor alpha gene polymorphism is associated with coronary artery disease severity

Background: Estrogens have beneficial effects on the cardiovascular system partially mediated by estrogen receptor alpha (ERa). Alternations in ERa expression may affect the atheroprotective role of estrogens. We hypothesized that genetic variation in the ragulatory region of the ERa gene is associated with the angiographic severity of CAD. Methods: We studied 496 consecubve patients (72% man. 28% women) who had coronary angiography. Severity of CAD was assessed by: 1) the number of major coronary vessels with at least one >50% narrowing (NMCV); 2) the number of vessels with any narrowing (NCV); 3) the total number of narrowings (NN). The length of the dinucleotide repeat thymine & adenine (TA repeats) upstream of axon 1 of the ERu gene, was determined by PCR. The median number of TA repeats was used to catagorrza the population into 3 groups: long alleles genotype (both alleles 218 repeats), short alleles genotype (both alleles ~18 repeats), and mrxed genotype (short 5 long allele). Since the contribution of genetic factors is expected to be more prominent in younger subjects, patients ware divided into younger and older groups, age55 (n=126) vs. age>55 (n=368). The relationship between TA length and the severity of CAD was assessed by analysis of covarranca, stratified by age group. Sex and major CAD risk factors (diabetes, hypertension, hyperlipidemia, smoking, obesfty, family history) ware included as confounding factors. Results: Young patients with long alleles genotype had a significantly greater number of harrowed coronary artehes compared to those with short alleles genotype (NCV 3.722.4 vs. 2.5_+1.8, respectively, ~~0.02). Similarly. young patients with long alleles had a higher total number of coronary narrowings compared to those with short alleles (NN 4.k2.7 vs. 3.1 i2.2. respectively, pcO.02). A trend towards a higher NMCV rn young pattents with long alleles was also observed (NMCV 2.021 .I vs. 1.6$3.9. long vs. short. p=NS). These differences were not observed in older patients. Conclusion: The length of the TA dkwcleotide repeat in the regulatory region of the ERu gene is associated with the angiographic severity of CAD in young subjects, Independent of the major coronary rusk factors.

Fimbrial ghf gene cluster of genital strains of Haemophilus spp.

We analyzed the LKP fimbrial gene clusters of six piliated strains of a cryptic genospecies of Haemophilus isolated from the genital tracts of adult patients (five strains) and from an infected neonate. In a group of 19 genital strains, LKP-like genes have been found in only these 6 strains. In addition to the ghfA, ghfD, and ghfE genes previously described, we characterized two genes, designated ghfB and ghfC, encoding the putative chaperone and assembly platform proteins. All six strains had a complete and unique LKP-like gene cluster consisting of the five genes ghfA to ghfE, homologous to genes hifA to hifE of Haemophilus influenzae. The sequences of the coding and intergenic regions of the ghf clusters of the six strains were remarkably homologous. Unlike hif clusters, which are inserted between purE and pepN, the ghf cluster was inserted between purK and pepN on the chromosome. Analysis of the flanking regions of the ghf cluster identified a large deletion, identical in the 5' end regions of all strains, including the whole purE gene and much of the purK gene. Ultrastructural observations, an attempt at enriching LKP fimbriae, and hemagglutination experiments demonstrated that none of the strains had LKP-type fimbriae. Nevertheless, reverse transcription (RT)-PCR showed that ghf genes were transcribed in four of the six strains. Sequencing of the intergenic ghfA-ghfB regions, including the ghf gene promoters, showed that the absence of transcripts in the remaining two strains was due to a decrease in the number of TA repeats (4 or 9 repeats rather than 10) between the -10 and -35 boxes of the two overlapping and divergent promoters. The other four strains, which had ghf transcripts, had the optimal 10 TA repeats (one strain) or 5 repeats associated with putative alternative -35 boxes (three strains). The absence of 10 repeated palindromic sequences of 44 or 45 nucleotides upstream of ghfB induces an increased instability of mRNA, as quantified by real-time RT-PCR, and may explain why the LKP fimbrial gene cluster is not expressed in these strains.

No relationship exists between itai-itai disease and TA repeat polymorphisms of the estrogen receptor alpha gene.

Itai-itai (ouch-ouch) disease is a syndrome accompanied by bone mineral disorders that may be related to oral cadmium exposure. Itai-itai predominantly affects postmenopausal women with a history of multiple childbirth. In a previous study we have examined the genotype distributions of PvuII and XbaI restriction fragment length polymorphisms of the estrogen receptor alpha (ER alpha) gene in patients with itai-itai disease and compared them with those of controls. However, no significant differences were shown between the genotype distributions of the patients and controls. In the present study, we determined the TA repeat polymorphisms of the patients and controls. The distributions of the patients were: HH 25.0%, HL 50.0%, and LL 25.0%; where HH includes two alleles with a high number of TA repeats (TA> or =16), HL includes one high number allele and one low number allele (TA< or =15), and LL includes two alleles with a low number of TA repeats. These patients' distributions were not significantly different from those of the controls. Although our sample number was limited, we concluded that a polymorphism variant of the ER alpha gene is not a predisposing factor for itai-itai disease.

Estrogen Receptor α Gene Polymorphisms and Bone Mineral Density: Haplotype Analysis in Women from the United Kingdom

Genetic factors are important in the pathogenesis of osteoporosis and the estrogen receptor has been suggested as a possible candidate gene for regulation of bone mineral density (BMD). We investigated the relationship between PvuII, XbaI, and dinucleotide (TA)n repeat polymorphisms of the estrogen receptor alpha (ER-alpha) gene and BMD in a study of women from northeast Scotland in the United Kingdom. No significant association was observed between BMD values at the lumbar spine (LS) and femoral neck (FN) in relation to PvuII and XbaI polymorphisms individually, but haplotype analysis showed that BMD values (Z score) were significantly lower in those who carried the Px haplotype (n = 36) compared with those who did not (n = 170) at both the LS (mean +/- SEM; -0.775 +/- 0.125 vs. -0.285 +/- 0.082;p = 0.002) and the FN (-0.888 +/- 0.130 vs. -0.335 +/- 0.083; p = 0.0006). In keeping with this, the Px haplotype also was found to be an independent predictor of LS BMD (p = 0.019) and FN BMD (p = 0.005) in a multiple regression analysis model that included other possible predictors of BMD including age, years since menopause (YSM), hormone-replacement therapy (HRT) use, weight, and height. This model explained 15.7% and 23.4% of the total observed variance in LS and FN BMD, respectively, with the Px haplotype accounting for approximately 3% of the variance at both sites. Although the TA repeat polymorphism was in strong linkage disequilibrium (LD) with the PvuII (chi2 = 109.8; p < 0.0001) and XbaI (chi2 = 97.2; p < 0.0001) polymorphisms, there was no overall association between TA repeat number and BMD. We conclude that polymorphisms of the ER-alpha gene are significantly related to BMD in our population and that this association is dependent on the Px haplotype, suggesting that it is the Px haplotype, or a linked polymorphism, that confers risk.

Bilirubin UDP-glucuronosyltransferase1A1 gene polymorphisms: Susceptibility to oxidative damage and cancer?

The UDP-glucuronosyltransferase 1A1 (UGT1A1) gene product catalyzes the glucuronidation of serum bilirubin as part of normal heme catabolism. Recently, TA repeat polymorphisms containing five, six, seven, and eight TA dinucleotides in a putative TATA box in the promoter region of the UGT1A1 gene have been described. TA repeat number modulates UGT1A1 transcriptional activity and the quantity of enzyme available to conjugate serum bilirubin. Serum bilirubin is a known antioxidant, and low serum bilirubin has been associated with increased risk for coronary artery disease and inhibition of reactive oxygen species (ROS)-induced damage to erythrocytes in vitro. We hypothesize that the UGT1A1 TA repeats or other functional polymorphisms resulting in lower serum bilirubin levels may be predictive of genetic susceptibility to oxidative damage and cancer. Exposure-related or endogenous production of ROS may impact the integrity of cellular macromolecules and infrastructure, lead to DNA base changes or chromosomal aberrations, and induce toxicity or apoptosis. ROS damage to lipoproteins may be a factor in formation of atherogenic plaques in coronary heart disease. Thus, cellular oxidative stress could contribute to tumorigenesis through mutagenic or epigenetic pathways, and higher serum bilirubin levels should inhibit this process. No definitive studies have been performed, but in a small prospective study of colon cancer, serum bilirubin levels were observed to be lower in these cases. Another study has suggested a link between UGT1A1 alleles, estrogen metabolism, and risk in breast cancer. Epidemiologic studies examining variation in ROS metabolism, ROS damage, bilirubin, and cancer risk will demonstrate the value of this hypothesis.

Bilirubin UDP‐glucuronosyltransferase 1A1 gene polymorphisms: Susceptibility to oxidative damage and cancer?

The UDP-glucuronosyltransferase 1A1 (UGT1A1) gene product catalyzes the glucuronidation of serum bilirubin as part of normal heme catabolism. Recently, TA repeat polymorphisms containing five, six, seven, and eight TA dinucleotides in a putative TATA box in the promoter region of the UGT1A1 gene have been described. TA repeat number modulates UGT1A1 transcriptional activity and the quantity of enzyme available to conjugate serum bilirubin. Serum bilirubin is a known antioxidant, and low serum bilirubin has been associated with increased risk for coronary artery disease and inhibition of reactive oxygen species (ROS)–induced damage to erythrocytes in vitro. We hypothesize that the UGT1A1 TA repeats or other functional polymorphisms resulting in lower serum bilirubin levels may be predictive of genetic susceptibility to oxidative damage and cancer. Exposure-related or endogenous production of ROS may impact the integrity of cellular macromolecules and infrastructure, lead to DNA base changes or chromosomal aberrations, and induce toxicity or apoptosis. ROS damage to lipoproteins may be a factor in formation of atherogenic plaques in coronary heart disease. Thus, cellular oxidative stress could contribute to tumorigenesis through mutagenic or epigenetic pathways, and higher serum bilirubin levels should inhibit this process. No definitive studies have been performed, but in a small prospective study of colon cancer, serum bilirubin levels were observed to be lower in these cases. Another study has suggested a link between UGT1A1 alleles, estrogen metabolism, and risk in breast cancer. Epidemiologic studies examining variation in ROS metabolism, ROS damage, bilirubin, and cancer risk will demonstrate the value of this hypothesis. Mol. Carcinog. 29:198–204, 2000. © Published 2000 Wiley-Liss, Inc.

A TA repeat polymorphism in the estrogen receptor gene is associated with osteoporotic fractures but polymorphisms in the first exon and intron are not.

Estrogen and the estrogen receptor (ER) play a central role in bone metabolism as illustrated by the loss of bone mass after menopause and the osteopenia in individuals with defect aromatase or ER. We therefore wanted to investigate the effect of polymorphisms in the ER-alpha gene on bone mass, bone turnover, and the prevalence of osteoporotic fractures in a study of 160 women and 30 men with vertebral fractures and 124 women and 64 men who are normal. Three previously described polymorphisms, G261-C in exon 1 and T-C and A-G in intron 1, in the ER gene were determined by restriction fragment length polymorphism (RFLP) using BstUI, Pvu II, and Xba I after polymerase chain reaction (PCR). A TA repeat polymorphism in the promoter region was examined by PCR and electrophoresis. The distribution of BstUI, Pvu II, and Xba I RFLPs was similar in the osteoporotic patients and the normal controls. No significant differences could be shown in bone mass or bone turnover between the genotypes. The mean number of TA repeats was lower in patients with osteoporotic fractures, 17.3+/-2.8 versus 18.6+/-2.8 in the normal controls (p < 0.01). This also was reflected in a significantly increased odds ratio of osteoporotic fractures in individuals with 11-18 repeats of 2.64 (95% CIs, 1.61-4.34). Furthermore, bone mineral density (BMD) of the lumbar spine was lower in individuals with low mean number of repeats than in individuals with high mean number of repeats (0.790+/-0.184 g/cm2 vs. 0.843+/-0.191 g/cm2; p < 0.05). This difference also was found in BMD of the total hip. Using multiple linear regression, mean number of TA repeats was a predictor of lumbar spine BMD (p < 0.05) and a BMD-independent predictor of fractures (p < 0.05). Mean number of TA repeats was not associated with levels of biochemical markers of bone turnover. All four polymorphisms were in linkage disequilibrium. A TA repeat polymorphism in the ER gene is associated with increased risk of osteoporotic fractures and a modest reduction in bone mass. Polymorphisms in the first exon and first intron of the ER gene are not associated with osteoporotic fractures, bone mass, or bone turnover.

Variability at the uridine diphosphate glucuronosyltransferase 1A1 promoter in human populations and primates

Variation at the UDP-glucuronosyltransferase (UGT) 1A1 gene promoter is present in humans. Variable numbers of TA repeats in the TATA box of this gene are found which are inversely related to levels of gene expression. We investigated this polymorphism in 658 individuals from a worldwide sample of 15 aboriginal and two admixed human populations. This study shows that there is a great deal of variability across ethnic groups with regard to UGT1A1 allele frequencies, with the most common allele varying in frequency from 33% to 91%. Populations of African origin harbor four different alleles while non-African populations appear to have only two alleles. In addition, alleles associated with lower gene expression levels reach the highest frequencies in populations of African origin and lowest among Asians and Amerindians. Thus, more variability in the metabolism of drugs eliminated by UGT1A1 glucuronidation should be expected in populations of Sub-Saharan African origin. The sequence analysis of nine primate species shows that the number of TA repeats has increased during primate evolution achieving the largest number in humans. We suggest that the UGT1A1 promoter variability does not reflect historical relationships between populations and that it may be maintained by natural selection. Our findings are consistent with the proposal that the TA repeat variation is a balanced polymorphism.

Phenotype-genotype correlation of in vitro SN-38 (active metabolite of irinotecan) and bilirubin glucuronidation in human liver tissue with UGT1A1 promoter polymorphism.

Hepatic uridine diphosphate glucuronosyltransferase (UGT) isoform 1A1 (UGT1A1) is primarily responsible for the glucuronidation of SN-38 (7-ethyl-10-hydroxycamptothecin), the active metabolite of the anticancer agent irinotecan. UGT1A1, also catalyzing the glucuronidation of bilirubin, has been shown to have reduced activity in Gilbert's syndrome. The presence of an additional TA repeat [(TA)7TAA] in the TATA sequence of UGT1A1 has been associated with Gilbert's syndrome. To evaluate the relationship between UGT1A1 phenotypic activity and UGT1A1 promoter polymorphism. Phenotypic measurements included in vitro SN-38 and bilirubin glucuronidation in human liver microsomes (n = 44). A recently developed genotyping test was used to determine TATA sequence polymorphisms in UGT1A1. Genotypes were assigned as follows: 7/7, homozygous for the (TA)7TAA allele; 6/6, homozygous for the (TA)6TAA allele; and 6/7, heterozygous with 1 of each allele. Nine percent of screened liver samples were found to be homozygous for allele 7 (7/7), 43% were homozygous for allele 6 (6/6), and 48% were heterozygous (6/7). Frequencies of (TA)7TAA and (TA)6TAA alleles were 0.33 and 0.67, respectively. A significant trend toward a decrease in SN-38 and bilirubin glucuronidation rates was found as the number of TA repeats increased (6/6 > 6/7 > 7/7). Glucuronidation rates of both substrates were significantly lower in the 7/7 and 6/7 groups compared with the 6/6 group. The results indicate a significant association of UGT1A1 phenotype and genotype based on in vitro phenotypic measurements. The clinical significance of our finding remains to be established.