Common variants of four bilirubin metabolism genes and their association with serum bilirubin and coronary artery disease in Chinese Han population. Pharmacogenet Genomics. 2009;19:310-318. [PMID: 19238116 DOI: 10.1097/fpc.0b013e328328f818]

Genetic determinants of serum bilirubin using inferred native American gene variants in Chilean adolescents

Gene variants in the UGT1A1 gene are strongly associated with circulating bilirubin levels in several populations, as well as other variants of modest effect across the genome. However, the effects of such variants are unknown regarding the Native American ancestry of the admixed Latino population. Our objective was to assess the Native American genetic determinants of serum bilirubin in Chilean admixed adolescents using the local ancestry deconvolution approach. We measured total serum bilirubin levels in 707 adolescents of the Chilean Growth and Obesity Cohort Study (GOCS) and performed high-density genotyping using the Illumina-MEGA array (>1.7 million genotypes). We constructed a local ancestry reference panel with participants from the 1000 Genomes Project, the Human Genome Diversity Project, and our GOCS cohort. Then, we inferred and isolated haplotype tracts of Native American, European, or African origin to perform genome-wide association studies. In the whole cohort, the rs887829 variant and others near UGT1A1 were the unique signals achieving genome-wide statistical significance (b = 0.30; p = 3.34 × 10-57). After applying deconvolution methods, we found that significance is also maintained in Native American (b = 0.35; p = 3.29 × 10-17) and European (b = 0.28; p = 1.14 × 10-23) ancestry components. The rs887829 variant explained a higher percentage of the variance of bilirubin in the Native American (37.6%) compared to European ancestry (28.4%). In Native American ancestry, carriers of the TT genotype of this variant averaged 4-fold higher bilirubinemia compared to the CC genotype (p = 2.82 × 10-12). We showed for the first time that UGT1A1 variants are the primary determinant of bilirubin levels in Native American ancestry, confirming its pan-ethnic relevance. Our study illustrates the general value of the local ancestry deconvolution approach to assessing isolated ancestry effects in admixed populations.

Etiology analysis for term newborns with severe hyperbilirubinemia in eastern Guangdong of China

BACKGROUND

Neonatal hyperbilirubinemia is one of the common diseases of newborns that typically presents with yellow staining of skin, resulting in sequelaes such as hearing loss, motor and intellectual development disorders, and even death. The pathogenic factors of neonatal hyperbilirubinemia are complex. Different cases of hyperbilirubinemia may have a single or mixed etiology.

AIM

To explore the etiological characteristics of severe hyperbilirubinemia in term newborns of eastern Guangdong of China.

METHODS

Term newborns with severe hyperbilirubinemia in one hospital from January 2012 to December 2021 were retrospectively analyzed. The etiology was determined according to the laboratory results and clinical manifestations.

RESULTS

Among 1602 term newborns with hyperbilirubinemia in eastern Guangdong of China, 32.20% (580/1602) was severe hyperbilirubinemia. Among the causes of severe hyperbilirubinemia, neonatal hemolysis accounted for 15.17%, breast milk jaundice accounted for 12.09%, infection accounted for 10.17%, glucose-6-phosphate dehydrogenase (G6PD) deficiency accounted for 9.14%, and the coexistence of multiple etiologies accounted for 6.55%, unknown etiology accounted for 41.72%. ABO hemolysis and G6PD deficiency were the most common causes in the 20 cases with bilirubin encephalopathy. 94 severe hyperbilirubinemia newborns were tested for uridine diphosphate glucuronosyl transferase 1A1 (UGT1A1)*6 variant (rs4148323, c.211G>A, p.Arg71Gly), 9 cases were 211 G to A homozygous variant, 37 cases were 211 G to A heterozygous variant, and 48 cases were wild genotypes.

CONCLUSION

The main cause for severe hyperbilirubinemia and bilirubin encephalopathy in eastern Guangdong of China were the hemolytic disease of the newborns, G6PD deficiency and infection. UGT1A1 gene variant was also a high-risk factor for neonatal hyperbilirubinemia. Targeted prevention and treatment according to the etiology may reduce the occurrence of bilirubin encephalopathy and kernicterus.

Co-inheritance of G6PD deficiency and 211 G to a variation of UGT1A1 in neonates with hyperbilirubinemia in eastern Guangdong

Background

Glucose-6-phosphate dehydrogenase (G6PD) deficiency, which may manifest as neonatal hyperbilirubinemia, is the most prevalent erythrocytic enzyme-related disease in the world.

Objective

To investigate the association between neonatal hyperbilirubinemia and co-inheritance of G6PD deficiency and 211 G to A variation of UGT1A1 in Chaozhou city of eastern Guangdong province, the effects of G6PD deficiency and UGT1A1 gene variant on the bilirubin level were determined in neonates with hyperbilirubinemia.

Method

The activity of G6PD was assayed by an auto-bioanalyzer. PCR and flow-through hybridization were used to detect 14 common G6PD mutations in G6PD deficient neonates. 211 G to A variation of UGT1A1 was determined by PCR and sequencing. The data of neonatal bilirubin was collected and analyzed retrospectively.

Results

Seventy four cases of the 882 hyperbilirubinemia neonates were G6PD deficiency (8.39%) while 12 cases of the 585 non-hyperbilirubinemia neonates (control group) were G6PD deficiency (2.05%). The rate of G6PD deficiency in the hyperbilirubinemia group was higher than that of the control group. Moreover, the peak bilirubinin of the G6PD-deficient group of hyperbilirubinemia neonates was 334.43 ± 79.27 μmol/L, higher than that of the normal G6PD group of hyperbilirubinemia neonates (300.30 ± 68.62 μmol/L). The most common genotypes of G6PD deficiency were c.1376G > T and c.1388G > A, and the peak bilirubin of neonates with these two variants were 312.60 ± 71.81 μmol/L and 367.88 ± 75.79 μmol/L, respectively. The bilirubin level of c.1388G > A was significantly higher than that of c.1376G > T. Among the 74 hyperbilirubinemia neonates with G6PD deficiency, 6 cases were 211 G to A homozygous mutation (bilirubin levels 369.55 ± 84.51 μmol/L), 27 cases were 211 G to A heterozygous mutation (bilirubin levels 341.50 ± 63.21 μmol/L), and 41 cases were wild genotypes (bilirubin levels 324.63 ± 57.52 μmol/L).

Conclusion

The rate of G6PD deficiency in hyperbilirubinemia neonates was significantly higher than that of the non-hyperbilirubinemia neonates in Chaozhou. For the hyperbilirubinemia group, neonates with G6PD deficiency had a higher bilirubin level compared to those with normal G6PD. For hyperbilirubinemia neonates with G6PD deficiency, there was a declining trend of bilirubin levels among 211 G to A homozygous mutation, heterozygous mutation, and wild genotype, but there was no significance statistically among the three groups.

Ensemble learning for the early prediction of neonatal jaundice with genetic features

BACKGROUND

Neonatal jaundice may cause severe neurological damage if poorly evaluated and diagnosed when high bilirubin occurs. The study explored how to effectively integrate high-dimensional genetic features into predicting neonatal jaundice.

METHODS

This study recruited 984 neonates from the Suzhou Municipal Central Hospital in China, and applied an ensemble learning approach to enhance the prediction of high-dimensional genetic features and clinical risk factors (CRF) for physiological neonatal jaundice of full-term newborns within 1-week after birth. Further, sigmoid recalibration was applied for validating the reliability of our methods.

RESULTS

The maximum accuracy of prediction reached 79.5% Area Under Curve (AUC) by CRF and could be marginally improved by 3.5% by including genetic variant (GV). Feature importance illustrated that 36 GVs contributed 55.5% in predicting neonatal jaundice in terms of gain from splits. Further analysis revealed that the main contribution of GV was to reduce the false-positive rate, i.e., to increase the specificity in the prediction.

CONCLUSIONS

Our study shed light on the theoretical and practical value of GV in the prediction of neonatal jaundice.

APOE gene ɛ4 allele (388C-526C) effects on serum lipids and risk of coronary artery disease in southern Chinese Hakka population

OBJECTIVE

To analyze the relationship of Apolipoprotein E (APOE) and solute carrier organic anion transporter family member 1B1 (SLCO1B1) gene polymorphisms with coronary artery disease (CAD).

METHODS

1,129 CAD patients and 1,014 non-CAD controls were included in the study, and relevant information and medical records were collected. The single-nucleotide polymorphisms (SNPs) were analyzed, including rs429358, rs7412 in APOE gene and rs2306283, rs4149056 in SLCO1B1 gene.

RESULTS

The CAD patients' average age was 66.3 ± 10.7 years, while 65.5 ± 12.0 years in controls. The frequencies of APOE allele ɛ3, ɛ4, and ɛ2 were 83.01%, 10.08%, and 6.91% respectively. There were statistically significant differences in genotype ɛ3/ɛ4 (χ²  = 8.077, p = 0.005) in CAD patients compared with the controls. The SLCO1B1 genotype *1b/*1b and haplotype *1b showed the highest frequency in the study sample. Moreover, ε4 carriers had significantly lower HDL-C, Apo-A1 levels than ε3 carriers among CAD patients, while ε2 carriers showed lower LDL-C, Apo-B level, and higher Apo-A1/Apo-B level than ε3 and ε4 carriers. In controls, ε2 carriers showed lower LDL-C and Apo-B level, higher Apo-A1, and Apo-A1/Apo-B level than ε4 carriers. Logistic regression analysis showed that high LDL-C and Apo-B level, low HDL-C level, smoking, and the ε4 allele were risks for the presence of CAD.

CONCLUSIONS

APOE ε4 allele may be associated with susceptibility to CAD in southern Chinese Hakka population. It indicated that the APOE SNPs rs429358 and rs7412 are associated with CAD, but not SNPs rs2306283 and rs4149056 of SLCO1B1 gene.

A UGT1A1 variant is associated with serum total bilirubin levels, which are causal for hypertension in African-ancestry individuals

Serum bilirubin is associated with several clinical outcomes, including hypertension, type 2 diabetes (T2D), and drug metabolism. Here, we describe findings from our genome-wide association studies (GWAS) of serum (TBIL) using a generalized linear mixed model in West Africans (n = 1127), with adjustment for age, sex, body mass index, T2D, significant principal components of population structure, and cryptic relatedness. Genome-wide conditional analysis and CAVIARBF were used to fine map significant loci. The causal effect of TBIL on hypertension was assessed by Mendelian randomization (MR) using the GWAS findings as instrumental variables (IVs) in African Americans (n = 3,067). The SNP rs887829 (UGT1A1) was significantly associated with TBIL levels (effect allele (T) frequency = 0.49, β (SE) = 0.59 (0.04), p = 9.13 × 10^-54). Genome-wide conditional analysis and regional fine mapping pointed to rs887829 as a possible causal variant with a posterior inclusion probability of 0.99. The T allele of rs887829 is associated with lower hepatic expression of UGT1A1. Using rs887829 as an IV, two-stage least-squares MR showed a causal effect of bilirubin on hypertension (β = -0.76, 95% CI [-1.52, -0.01], p = 0.0459). Our finding confirms that UGT1A1 influences bilirubin levels. Notably, lower TBIL is causally associated with the increased risk of hypertension.

Compound heterozygous UGT1A1*28 and UGT1A1*6 or single homozygous UGT1A1*28 are major genotypes associated with Gilbert's syndrome in Chinese Han people

Gilbert's syndrome (GS) is a mild condition characterized by periods of hyperbilirubinemia, which results in variations in the UDP-glucuronosyltransferase 1 (UGT1A1) gene. Variant genotypes of UGT1A1 vary in different populations in the world. The present study aimed to determine the genotype of the UGT1A1 promoter and exon that are related to the serum total bilirubin (STB) level in the Chinese Han population. A total of 120 individuals diagnosed with GS (GS group) and 120 healthy individuals (non-GS group) were enrolled. Routine blood, liver function tests, and antibodies associated with autoimmune liver diseases were assessed. Blood samples were collected for DNA purification. Sequencing of the UGT1A1 promoter and exons was conducted for post segment amplification by PCR. Compound heterozygous UGT1A1*28 and UGT1A1*6 (25/120, 20.83%), single homozygous UGT1A1*28 (24/120, 20.00%) and single heterozygous UGT1A1*6 (18/120, 15.00%) were the most frequent genotypes in the GS group. However, single heterozygous UGT1A1*6 (30/120, 25.00%) and single heterozygous UGT1A1*28 (19/120, 15.83%) were the most frequent genotypes in the non-GS group. Further, the frequencies of single homozygous UGT1A1*28, compound heterozygous UGT1A1*28 and UGT1A1*6, and compound heterozygous UGT1A1*28, UGT1A1*6 and UGT1A1*27 were significantly higher in the GS group than those in the non-GS group. The STB levels of GS patients with the homozygous UGT1A1*28 genotype were remarkably higher than those of patients with other genotypes. Homozygous UGT1A1*28 and heterozygous UGT1A1*6 variants were associated with the highest and lowest risks of hyperbilirubinemia, respectively. Our study revealed that compound heterozygous UGT1A1*28 and UGT1A1*6, or single homozygous UGT1A1*28 are major genotypes associated with GS in Chinese Han people. These findings might facilitate the precise genomic diagnosis of Gilbert's syndrome.

The Relationship Between Serum Bilirubin Levels and Peripheral Arterial Disease and Gender Difference in Patients With Hypertension: BEST Study

We evaluated the relationship between serum bilirubin levels and ankle-brachial index (ABI) to determine whether gender affected the relationship between bilirubin levels and peripheral arterial disease (PAD) in patients with hypertension. A total of 543 patients were included in our studies (78 patients with PAD and 465 without PAD). Peripheral arterial disease was defined as ABI <0.90 for either and/or both sides. Serum bilirubin levels were measured with a vanadate oxidation method by using fasting venous blood samples. Serum total bilirubin (TBiL) and direct bilirubin (DBiL) levels were higher in males compared with females (both P < .05). Total bilirubin and DBiL were significantly lower in the PAD group. After adjustment for cardiovascular risk factors, PAD was independently negatively related to TBiL and DBiL, with odds ratios (OR) 0.914 (95% confidence interval [CI]: 0.845-0.990) and 0.748 (95% CI: 0.572-0.977). In addition, there was a relationship between PAD and bilirubin levels (TBiL-OR = 0.884, 95% CI: 0.792-0.985; DBiL-OR = 0.621; 95% CI: 0.424-0.909) only in males but not in females. Future studies should further evaluate whether interventions that increase serum bilirubin levels will have a particular role in PAD prevention in males.

Serum Bilirubin and Coronary Artery Disease: Intricate Relationship, Pathophysiology, and Recent Evidence

Coronary artery disease (CAD) is a major cause of morbidity, mortality, and healthcare expenditure. A number of environmental and genetic risk factors have been known to contribute to CAD. More recently, a number of studies have supported as well as opposed a possible protective benefit of bilirubin in CAD, since it has anti-inflammatory, antioxidant, and antiaggregatory properties that may reduce atherogenesis. It also shares associations with different forms of CAD, namely stable CAD, unstable angina pectoris, stable angina pectoris, and acute myocardial infarction. Lack of sufficient evidence, however, has failed to elucidate a causal relationship between serum bilirubin level and risk of CAD. Therefore, in this update, we attempted to simplify this intricate relationship between bilirubin and CAD, revisit the pathophysiology of disease, how bilirubin may be protective, and to summarize the findings of the current literature.

Genetically Regulated Bilirubin and Risk of Non-alcoholic Fatty Liver Disease: A Mendelian Randomization Study

Mildly elevated serum bilirubin levels were reported to be associated with decreased risk of non-alcoholic fatty liver disease (NAFLD). Whether this is a causal relationship remains unclear. We tested the hypothesis that genetically elevated plasma bilirubin levels are causally related to reduce risk of NAFLD. A total of 403 eligible participants were enrolled. NAFLD was determined by liver ultrasonography. The uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) gene variants (UGT1A1^*6 and UGT1A1^*28) were genotyped through sequencing. We applied a Mendelian randomization approach to assess the effects of genetically elevated bilirubin levels on NAFLD. NAFLD was diagnosed in 19% of participants in our study (NAFLD = 76; Non-NAFLD = 327). The variants of UGT1A1^*28 and UGT1A1^*6 were strongly associated with increased total bilirubin (TB), direct bilirubin (DB), and indirect bilirubin (IB) levels (each P < 0.001). These two common variants explain 12.7% (TB), 11.4% (IB), and 10.2% (DB) of the variance in bilirubin levels, respectively. In logistic regression model, after multifactorial adjustment for sex, age, aminotransferase (ALT), white blood count (WBC), and body mass index (BMI), variant UGT1A1^*28 (OR = 1.39; 95%CI: 0.614–3.170; P = 0.43) and UGT1A1^*6 (OR = 1.64, 95%CI, 0.78–3.44; P = 0.19) genotypes were not significantly associated with the risk of NAFLD. Moreover, the plasma bilirubin level (TB, IB, and DB) were not significantly associated with the risk of NAFLD (P > 0.30). A Mendelian randomization analysis of the UGT1A1 variants suggests that bilirubin is unlikely causally related with the risk of NAFLD.

Heme oxygenase-1 gene promoter polymorphisms are associated with coronary heart disease and restenosis after percutaneous coronary intervention: a meta-analysis

Numerous published studies have suggested that there is association between heme oxygenase-1 (HO-1) gene polymorphisms and coronary heart disease (CHD) or restenosis (RS) after percutaneous coronary intervention (PCI). This study aimed to clarify this association using a meta-analysis method. We used a systematic search for studies on the association of HO-1gene polymorphisms with CHD or RS in PubMed, Web of Science, the Cochrane Library, Wanfang Data and CNKI (China National Knowledge Infrastructure). We used Stata 12.0 software to perform the meta-analyses. Twenty-three studies, involving 12,130 patients with CHD or RS and 14,181 controls, were included. A statistically significant association between the HO-1(GT)n repeat length polymorphism and CHD was observed under allelic (odds ratio (OR) = 0.929, 95% confidence interval (CI) = 0.881-0.978, p= 0.005), recessive (OR = 0.858, 95%CI = 0.780-0.945, p= 0.002), and co-dominant (OR = 0.843, 95%CI = 0.754-0.942, p= 0.003) models. Moreover, we also found a statistically significant association between the HO-1(GT)n repeat length polymorphism and RS under allelic (OR = 0.718, 95%CI = 0.541-0.953, p= 0.022) and co-dominant (OR = 0.522, 95%CI = 0.306-0.889, p=0.017) models. We found a significant association of the HO-1T(−413)A single-nucleotide polymorphism (SNP) with CHD under allelic (OR = 0.915, 95%CI = 0.842-0.995, p= 0.038), recessive (OR = 0.869, 95%CI = 0.760-0.994, p= 0.041), and co-dominant (OR = 0.792, 95%CI = 0.663-0.946, p=0.010) models. Our study indicates that both the HO-1(GT)n repeat length polymorphism and the T(−413)A SNP are associated with decreased risk of CHD. The (GT)n repeat length polymorphism was associated with RS following PCI.

NPR-C gene polymorphism is associated with increased susceptibility to coronary artery disease in Chinese Han population: a multicenter study

To find a new locus that confers significant susceptibility to CAD in Chinese Han population, a genome-wide association study in 200 “extreme individuals” from a Shandong cohort and a pathway-based candidate gene study from a Shanghai cohort (293 CAD/293 controls) were simultaneously performed. Amongst them, 13 SNPs associated with CAD were selected to conduct validation and replication studies in additional 3363 CAD patients and 3148 controls. A novel locus rs700926 in natriuretic peptide receptor C (NPR-C) was identified in Shandong and Hubei cohorts. Then rs700926 and other nine tag SNPs were genotyped in four geographically different populations (Shandong, Shaanxi, Hubei and Sichuan cohorts), and 6 SNPs (rs700926, rs1833529, rs2270915, rs17541471, rs3792758 and rs696831) showed stronger association with CAD, regardless of single or combined analysis. We further genotyped rs2270915 and 10 additional tag SNPs in a central China cohort and identified rs12697273 and rs10066436 as the loci associated with CAD. All these positive associations remained significant after adjustment for traditional risk factors of CAD. NPR-C gene SNPs significantly contribute to CAD susceptibility in the Chinese Han population.

Elevated serum urate is a potential factor in reduction of total bilirubin: a Mendelian randomization study

Aim

A Mendelian randomization study (MRS) can be linked to a "natural" randomized controlled trial in order to avoid potential bias of observational epidemiology. We aimed to study the possible association between serum urate (SU) and total bilirubin (TBIL) using MRS.

Materials and Methods

An observational epidemiological study using ordinary least squares (OLS) regression and MRS using two-stage least square (TLS) regression was conducted to assess the effect of SU on TBIL. The comparison between the OLS regression and the TLS regression was analyzed by the Durbin-Hausman test. If the p value is significant, it suggests that the OLS regression cannot evaluate the relationship between exposure and outcome, and the TLS regression is precise; while if the p value is not significant, there would be no significant difference between the two regressions.

Results

A total of 3,753 subjects were analyzed. In OLS regression, there was no significant association between SU and TBIL in all subjects and subgroup analysis (all p > 0.05). However, MRS revealed a negative correlation between SU and TBIL after adjustment for confounders (beta = -0.021, p = 0.010). Further analysis was conducted in different SU subgroups, and results show that elevated SU was associated with a significant reduction in TBIL after adjustment for hyperuricemic subjects (beta = -0.053, p = 0.027). In addition, the results using the Durbin-Hausman test further confirmed a negative effect of SU on TBIL (p = 0.002 and 0.010, respectively).

Conclusions

This research shows for the first time that elevated SU was a potential causal factor in the reduction of TBIL and it provides strong evidence to resolve the controversial association between SU and TBIL.

Role of the Free Radicals in Mechanisms of Gallstone Formation: An EPR Study

The mechanism of gallstone formation is not well understood. Abnormal regulation of hepatic cholesterol, bile acid synthesis or esterification, deposition of cholesterol monohydrate crystals and gall bladder dysfunction are thought to be the principal metabolic aberrations that may cause gallstone formation. One plausible mechanism leading to these abnormalities is the role of free radicals, whose presence can be investigated using Electron Paramagnetic Resonance (EPR). Surgically removed gall bladder stones were used to obtain purified bilirubin, which was irradiated in vitro with visible light and measured with EPR in the presence of and without oxygen. EPR detected oxidized bilirubin free radical (BFR) (g = 2.003, ΔH = 1.0 mTl) in the gallstones. In vitro exposure of bilirubin to visible light in the presence of oxygen induced BFR formation; its intensity was radiation time dependent and decreased under the influence of β-carotene; irradiation in a vacuum did not generate BFRs. These results indicate the important role of oxidative processes (oxidation of bilirubin) in the gallstone formation. In oxidative stress, bilirubin acting as a second type photosensitizer undergoes rapid oxidation and free radical polymerization that plays an important role in the nucleation and deposition of gallstones.

Bilirubin in coronary artery disease: Cytotoxic or protective?

Bilirubin has traditionally been considered a cytotoxic waste product. However, recent studies have shown bilirubin to have anti-oxidant, anti-inflammatory, vasodilatory, anti-apoptotic and anti-proliferative functions. These properties potentially confer bilirubin a new role of protection especially in coronary artery disease (CAD), which is a low grade inflammatory process exacerbated by oxidative stress. In fact, recent literature reports an inverse relationship between serum concentration of bilirubin and the presence of CAD. In this article, we review the current literature exploring the association between levels of bilirubin and risk of CAD. We conclude that current evidence is inconclusive regarding the protective effect of bilirubin on CAD. A causal relationship between low serum bilirubin level and increased risk of CAD is not currently established.

Role of pharmacogenetics on deferasirox AUC and efficacy

AIM

We evaluated deferasirox pharmacokinetic according to SNPs in genes involved in its metabolism and elimination. Moreover, we defined a plasma area under the curve cut-off value predicting therapy response.

PATIENTS & METHODS

Allelic discrimination was performed by real-time PCR. Drug plasma concentrations were measured by a high performance liquid chromatography system coupled with an ultraviolet method.

RESULTS

Pharmacokinetic parameters were significantly influenced by UGT1A1 rs887829C>T, UGT1A3 rs1983023C>T and rs3806596A>G SNPs. Area under the curve cut-off values of 360 μg/ml/h for efficacy were here defined and 250 μg/ml/h for nonresponse was reported. UGT1A3 rs3806596GG and ABCG2 rs13120400CC genotypes were factors able to predict efficacy, whereas UGT1A3 rs3806596GG was a nonresponse predictor.

CONCLUSION

These data show how screening patient's genetic profile may help clinicians to optimize iron chelation therapy with deferasirox.

Exome-Wide Association Study Identifies New Low-Frequency and Rare UGT1A1 Coding Variants and UGT1A6 Coding Variants Influencing Serum Bilirubin in Elderly Subjects: A Strobe Compliant Article

Genome-wide association studies (GWASs) have identified loci contributing to total serum bilirubin level. However, no exome-wide approaches have been performed to address this question. Using exome-wide approach, we assessed the influence of protein-coding variants on unconjugated, conjugated, and total serum bilirubin levels in a well-characterized cohort of 773 ambulatory elderly subjects from Italy. Coding variants were replicated in 227 elderly subjects from the same area. We identified 4 missense rare (minor allele frequency, MAF < 0.5%) and low-frequency (MAF, 0.5%-5%) coding variants located in the first exon of the UGT1A1 gene, which encodes for the substrate-binding domain (rs4148323 [MAF = 0.06%; p.Gly71Arg], rs144398951 [MAF = 0.06%; p.Ile215Val], rs35003977 [MAF = 0.78%; p.Val225Gly], and rs57307513 [MAF = 0.06%; p.Ser250Pro]). These variants were in strong linkage disequilibrium with 3 intronic UGT1A1 variants (rs887829, rs4148325, rs6742078), which were significantly associated with total bilirubin level (P = 2.34 × 10(-34), P = 7.02 × 10(-34), and P = 8.27 × 10(-34)), as well as unconjugated, and conjugated bilirubin levels. We also identified UGT1A6 variants in association with total (rs6759892, p.Ser7Ala, P = 1.98 × 10(-26); rs2070959, p.Thr181Ala, P = 2.87 × 10(-27); and rs1105879, p.Arg184Ser, P = 3.27 × 10(-29)), unconjugated, and conjugated bilirubin levels. All UGT1A1 intronic variants (rs887829, rs6742078, and rs4148325) and UGT1A6 coding variants (rs6759892, rs2070959, and rs1105879) were significantly associated with gallstone-related cholecystectomy risk. The UGT1A6 variant rs2070959 (p.Thr181Ala) was associated with the highest risk of gallstone-related cholecystectomy (OR, 4.58; 95% CI, 1.58-13.28; P = 3.21 × 10(-3)). Using an exome-wide approach we identified coding variants on UGT1A1 and UGT1A6 genes in association with serum bilirubin level and hyperbilirubinemia risk in elderly subjects. UGT1A1 intronic single-nucleotide polymorphisms (SNPs) (rs6742078, rs887829, rs4148324) serve as proxy markers for the low-frequency and rare UGT1A1 variants, thereby providing mechanistic explanation to the relationship between UGT1A1 intronic SNPs and the UGT1A1 enzyme activity. UGT1A1 and UGT1A6 variants might be potentially associated with gallstone-related cholecystectomy risk.

Bilirubin as a potential causal factor in type 2 diabetes risk: a Mendelian randomization study

Circulating bilirubin, a natural antioxidant, is associated with decreased risk of type 2 diabetes (T2D), but the nature of the relationship remains unknown. We performed Mendelian randomization in a prospective cohort of 3,381 participants free of diabetes at baseline (age 28-75 years; women 52.6%). We used rs6742078 located in the uridine diphosphate-glucuronosyltransferase locus as an instrumental variable (IV) to study a potential causal effect of serum total bilirubin level on T2D risk. T2D developed in a total of 210 participants (6.2%) during a median follow-up period of 7.8 years. In adjusted analyses, rs6742078, which explained 19.5% of bilirubin variation, was strongly associated with total bilirubin (a 0.68-SD increase in bilirubin levels per T allele; P < 1 × 10(-122)) and was also associated with T2D risk (odds ratio [OR] 0.69 [95% CI 0.54-0.90]; P = 0.006). Per 1-SD increase in log-transformed bilirubin levels, we observed a 25% (OR 0.75 [95% CI 0.62-0.92]; P = 0.004) lower risk of T2D. In Mendelian randomization analysis, the causal risk reduction for T2D was estimated to be 42% (causal OR for IV estimation per 1-SD increase in log-transformed bilirubin 0.58 [95% CI 0.39-0.84]; P = 0.005), which was comparable to the observational estimate (Durbin-Wu-Hausman χ(2) test, P for difference = 0.19). These novel results provide evidence that an elevated bilirubin level is causally associated with the risk of T2D and support its role as a protective determinant.

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.

Comprehensive variant screening of the UGT gene family

PURPOSE

UGT1A1, UGT2B7, and UGT2B15 are well-known pharmacogenes that belong to the uridine diphosphate glucuronyltransferase gene family. For personalized drug treatment, it is important to study differences in the frequency of core markers across various ethnic groups. Accordingly, we screened single nucleotide polymorphisms (SNPs) of these three genes and analyzed differences in their frequency among five ethnic groups, as well as attempted to predict the function of novel SNPs.

MATERIALS AND METHODS

We directly sequenced 288 subjects consisting of 96 Korean, 48 Japanese, 48 Han Chinese, 48 African American, and 48 European American subjects. Subsequently, we analyzed genetic variability, linkage disequilibrium (LD) structures and ethnic differences for each gene. We also conducted in silico analysis to predict the function of novel SNPs.

RESULTS

A total of 87 SNPs were detected, with seven pharmacogenetic core SNPs and 31 novel SNPs. We observed that the frequencies of UGT1A1 *6 (rs4148323), UGT1A1 *60 (rs4124874), UGT1A1 *93 (rs10929302), UGT2B7 *2 (rs7439366), a part of UGT2B7 *3 (rs12233719), and UGT2B15 *2 (rs1902023) were different between Asian and other ethnic groups. Additional in silico analysis results showed that two novel promoter SNPs of UGT1A1 -690G>A and -689A>C were found to potentially change transcription factor binding sites. Moreover, 673G>A (UGT2B7), 2552T>C, and 23269C>T (both SNPs from UGT2B15) changed amino acid properties, which could cause structural deformation.

CONCLUSION

Findings from the present study would be valuable for further studies on pharmacogenetic studies of personalized medicine and drug response.

Gilbert's syndrome and the risk of death: a population-based cohort study

BACKGROUND AND AIMS

Gilbert's syndrome is a common familial hyperbilirubinemia that may reduce the risk of various age-related diseases because of the antioxidant properties of bilirubin. We conducted a large cohort study using The Health Improvement Network primary care database and compared all-cause mortality rates in those with and without Gilbert's syndrome.

METHODS

Mortality rates in patients with a diagnosis of Gilbert's syndrome and raised bilirubin level (n = 4266) were compared with those of patients with similar characteristics but with normal bilirubin levels (n = 21 968). Multivariate Poisson regression was also used to estimate adjusted mortality rate ratios.

RESULTS

During the 350 000 PYs of follow up across the Gilbert's and comparison cohorts, there were 1174 deaths. Mortality rates were 24/10 000 PYs in the Gilbert's cohort versus 50/10 000 PYs in the comparison cohort. Mortality rates were around half in patients with Gilbert's syndrome after accounting for sociodemographics and general health indicators (adjusted mortality rate ratio: 0.5 [95% confidence interval; 0.4-0.7; P < 0.001]).

CONCLUSIONS

Mortality rates observed for people with Gilbert's syndrome in the general population are almost half those of people without evidence of Gilbert's syndrome.

Gene polymorphisms in the heme degradation pathway and outcome of severe human sepsis

Heme and its breakdown products CO, Fe, and bilirubin are being recognized as signaling molecules or even therapeutic agents, but also exert adverse effects when released at high concentrations. Manipulating the pathway confers protection in rodent sepsis models via both control of free heme and formation of its first and higher-order products. Thus, regulatory elements present in human heme oxygenase 1 (HMOX1) and biliverdin reductases (BLVRA/B) genes might impact outcome. We tested whether a highly polymorphic (GT)n microsatellite and single-nucleotide polymorphisms in HMOX1 and BLVRA/B genes are associated with outcome of sepsis. Two cohorts (n = 430 and 398 patients) with severe sepsis were screened for single-nucleotide polymorphisms and/or the microsatellite by fragment length analysis and genotyping techniques. Heme oxygenase 1 plasma levels were determined in additional patients with severe sepsis (n = 92) by enzyme-linked immunosorbent assay. Based on mean Sepsis-related Organ Failure Assessment scores, patients homozygous for rs2071746 A allele or medium length (GT)n microsatellites of HMOX1 showed higher 28-day mortality (P = 0.047 and P = 0.033) in one cohort compared with other genotypes, whereas 90-day mortality rates showed no association. The T allele was less frequently observed in both cohorts than would be expected according to Hardy-Weinberg equilibrium. Heme oxygenase 1 plasma levels were elevated in septic patients, independent of the genotype. Single-nucleotide polymorphisms within BLVRA/B showed no association with outcome. Short (GT)n repeats that are in linkage disequilibrium with the T allele of rs2071746 in HMOX1 are associated with favorable outcome, whereas no association with gene variants of BLVRA/B, involved in the generation of higher-order metabolites, was noticed.

Genetically elevated bilirubin and risk of ischaemic heart disease: three Mendelian randomization studies and a meta-analysis

BACKGROUND

Elevated plasma levels of bilirubin, an endogenous antioxidant, have been associated with reduced risk of ischaemic heart disease (IHD) and myocardial infarction (MI). Whether this is a causal relationship remains unclear.

OBJECTIVE

We tested the hypothesis that elevated plasma bilirubin is causally related to decreased risk of IHD and MI.

DESIGN

We used a Mendelian randomization approach and three independent studies from Copenhagen, Denmark. We measured bilirubin in 43 708 white individuals from the general population, and genotyped rs6742078 G>T in the uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) gene in 67 068 individuals, of whom 11 686 had IHD.

RESULTS

Third versus first tertile of baseline bilirubin levels was associated with 134% increased bilirubin levels, with sex- and age-adjusted hazard ratios (HRs) of 0.86 [95% confidence interval (CI), 0.76-0.98; P = 0.02] for IHD and 0.81 (95% CI, 0.66-0.99; P = 0.04) for MI, but with corresponding multifactorially adjusted HRs of 0.93 (95% CI, 0.82-1.06; P = 0.29) and 0.90 (95% CI, 0.73-1.12; P = 0.35). UGT1A1 rs6742078 TT versus GG genotype was associated with 95% increased bilirubin levels (P < 0.001); TT versus GG genotype was associated with odds ratios (ORs) of 1.03 (95% CI, 0.96-1.11; P = 0.73) for IHD and 1.01 (95% CI, 0.92-1.12; P = 0.68) for MI. Finally, in a meta-analysis of the present three studies and eight previous studies including a total of 14 711 cases and 60 324 controls, the random effects OR for ischaemic cardiovascular disease for genotypes with approximately 100% increased bilirubin levels versus reference genotypes was 1.01 (95% CI, 0.88-1.16).

CONCLUSION

These data suggest that plasma bilirubin is not causally associated with risk of IHD.

Cardiovascular events as a function of serum bilirubin levels in a large, statin-treated cohort

BACKGROUND

Serum bilirubin is an endogenous antioxidant that is routinely measured before a statin is prescribed primarily to assess liver function, but the association with cardiovascular disease (CVD) in this population has not been explored.

METHOD AND RESULTS

We identified patients from a United Kingdom primary care database (The Health Improvement Network) with measurements of serum total bilirubin levels recorded 3 months before the first statin treatment between January 1, 2000, and December 31, 2010, and no history of liver disease or CVD. In total, 130 052 patients met the inclusion criteria, and after a median follow-up of 43 months, there were 7850 CVD events. In men, the incidence of CVD in the lowest decile category of bilirubin (1-6 μmol/L [0.06-0.35 mg/dL]) was 215 per 10 000 person-years compared with 163 per 10 000 person-years in the highest decile (19-40 μmol/L [1.1-2.3 mg/dL]). Similar differences were seen for women. After conventional CVD risk factors were accounted for, the associations with bilirubin were nonlinear (L shaped), and the models predicted that, compared with patients with a bilirubin level of 10 μmol/L (0.6 mg/dL), those with a similar CVD risk profile but a bilirubin level of 5 μmol/L (0.3 mg/dL) had an 18% (95% confidence interval, 9-27) higher risk of any CVD event, a 34% (95% confidence interval, 13-56) higher risk of myocardial infarction, and a 33% (95% confidence interval, 21-46) higher risk of death resulting from any cause.

CONCLUSIONS

Serum bilirubin level measured before a statin prescription to assess liver function is an independent risk factor for CVD and death in both men and women.

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.

Mayo Genome Consortia: a genotype-phenotype resource for genome-wide association studies with an application to the analysis of circulating bilirubin levels

OBJECTIVE

To create a cohort for cost-effective genetic research, the Mayo Genome Consortia (MayoGC) has been assembled with participants from research studies across Mayo Clinic with high-throughput genetic data and electronic medical record (EMR) data for phenotype extraction.

PARTICIPANTS AND METHODS

Eligible participants include those who gave general research consent in the contributing studies to share high-throughput genotyping data with other investigators. Herein, we describe the design of the MayoGC, including the current participating cohorts, expansion efforts, data processing, and study management and organization. A genome-wide association study to identify genetic variants associated with total bilirubin levels was conducted to test the genetic research capability of the MayoGC.

RESULTS

Genome-wide significant results were observed on 2q37 (top single nucleotide polymorphism, rs4148325; P=5.0 × 10(-62)) and 12p12 (top single nucleotide polymorphism, rs4363657; P=5.1 × 10(-8)) corresponding to a gene cluster of uridine 5'-diphospho-glucuronosyltransferases (the UGT1A cluster) and solute carrier organic anion transporter family, member 1B1 (SLCO1B1), respectively.

CONCLUSION

Genome-wide association studies have identified genetic variants associated with numerous phenotypes but have been historically limited by inadequate sample size due to costly genotyping and phenotyping. Large consortia with harmonized genotype data have been assembled to attain sufficient statistical power, but phenotyping remains a rate-limiting factor in gene discovery research efforts. The EMR consists of an abundance of phenotype data that can be extracted in a relatively quick and systematic manner. The MayoGC provides a model of a unique collaborative effort in the environment of a common EMR for the investigation of genetic determinants of diseases.

Bilirubin, cardiovascular diseases and cancer: epidemiological perspectives

Owing to a potent antioxidant property of bilirubin, a growing interest has been drawn to the potential protective effects of bilirubin against oxidative stress-related diseases. This article evaluates associations of bilirubin with atherosclerotic diseases and cancer. Serum bilirubin has consistently been shown to be inversely associated with diverse atherosclerotic diseases, mostly among men in different populations. A limited number of prospective studies have shown a U-shaped or reversed J-shaped relationship between bilirubin and coronary heart disease in men and no evident association in women. Few studies have provided evidence supportive of a protective association between bilirubin and cancer risk. The findings on bilirubin-related genetic polymorphisms are inconsistent in relation to coronary heart disease and cancer.

Serum bilirubin and genes controlling bilirubin concentrations as biomarkers for cardiovascular disease

BACKGROUND

Serum bilirubin has been consistently shown to be inversely related to cardiovascular disease (CVD). Recent studies showed serum bilirubin to be associated with CVD-related factors such as diabetes, metabolic syndrome, and body mass index. Although the association of serum bilirubin with CVD has been found in both retrospective and prospective studies, less information is available on the role of genes that control bilirubin concentrations and their association with CVD.

CONTENT

In this review, we provide detailed information on the identity of the major genes that control bilirubin concentrations and their association with serum bilirubin concentrations and CVD risk. We also update the results of the major studies that have been performed on the association between serum bilirubin, CVD, and CVD-related diseases such as diabetes or metabolic syndrome. Studies consistently indicate that bilirubin concentrations are inversely associated with different types of CVD and CVD-related diseases. A conditional linkage study indicates that UGT1A1 is the major gene controlling serum bilirubin concentrations, and this finding has been confirmed in recent genomewide association studies. Studies also indicate that individuals homozygous for UGT1A1*28 have a significantly lower risk of developing CVD than carriers of the wild-type alleles.

SUMMARY

Serum bilirubin has a protective effect on CVD and CVD-related diseases, and UGT1A1 is the major gene controlling serum bilirubin concentrations. Pharmacologic, nonpharmacologic, or genetic interventions that increase serum bilirubin concentrations could provide more direct evidence on the role of bilirubin in CVD prevention.