Inheritance of hyperbilirubinemia: evidence for a major autosomal recessive gene

Association of Serum Bilirubin Level with Metabolic Syndrome and Non-Alcoholic Fatty Liver Disease: A Cross-Sectional Study of 1672 Obese Children

As in adults, obesity also plays a central role in the development of metabolic syndrome (MS) in children. Non-alcoholic fatty liver disease (NAFLD) is considered a manifestation of MS. Not only MS but also NAFLD seem to be inversely associated with serum bilirubin concentrations, an important endogenous tissue protector when only mild elevated. The aim of the study was to evaluate the association between serum bilirubin levels and the prevalence of MS and NAFLD in Italian obese children and adolescents. A retrospective cross-sectional study was performed in 1672 patients aged from 5 to 18 years. Clinical and laboratory parameters were assessed. NAFLD was measured by liver ultrasonography. The study was approved by the Ethical Committee of the Istituto Auxologico Italiano (research project code 1C021_2020, acronym BILOB). MS was present in 24% and fatty liver (FL) in 38% of this population. Bilirubin was not associated with FL and MS as a whole, but it was inversely associated only with selected components of MS, i.e., large WC, high blood pressure and high triglycerides. Our data suggest that bilirubin is not protective against MS and NAFLD in the presence of severe obesity.

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.

Metabolic abnormalities in Williams-Beuren syndrome

BACKGROUND

Williams-Beuren syndrome (WBS, OMIM-194050) is a neurodevelopmental disorder with multisystemic manifestations caused by a 1.55-1.83 Mb deletion at 7q11.23 including 26-28 genes. Reported endocrine and metabolic abnormalities include transient hypercalcaemia of infancy, subclinical hypothyroidism in ∼ 30% of children and impaired glucose tolerance in ∼ 75% of adult individuals. The purpose of this study was to further study metabolic alterations in patients with WBS, as well as in several mouse models, to establish potential candidate genes.

METHODS

We analysed several metabolic parameters in a cohort of 154 individuals with WBS (data available from 69 to 151 cases per parameter), as well as in several mouse models with complete and partial deletions of the orthologous WBS locus, and searched for causative genes and potential modifiers.

RESULTS

Triglyceride plasma levels were significantly decreased in individuals with WBS while cholesterol levels were slightly decreased compared with controls. Hyperbilirubinemia, mostly unconjugated, was found in 18.3% of WBS cases and correlated with subclinical hypothyroidism and hypotriglyceridemia, suggesting common pathogenic mechanisms. Haploinsufficiency at MLXIPL and increased penetrance for hypomorphic alleles at the UGT1A1 gene promoter might underlie the lipid and bilirubin alterations. Other disturbances included increased protein and iron levels, as well as the known subclinical hypothyroidism and glucose intolerance.

CONCLUSIONS

Our results show that several unreported biochemical alterations, related to haploinsufficiency for specific genes at 7q11.23, are relatively common in WBS. The early diagnosis, follow-up and management of these metabolic disturbances could prevent long-term complications in this disorder.

Potential cardiovascular risk protection of bilirubin in end-stage renal disease patients under hemodialysis

We evaluated the potential cardiovascular risk protection of bilirubin in hemodialysis (HD) patients. An enlarged set of studies were evaluated in 191 HD patients, including hematological study, lipid profile, iron metabolism, nutritional, inflammatory markers, and dialysis adequacy. The TA duplication screening in the UDP-glucuronosyltransferase 1 A1 (UGT1A1) promoter region was also performed. The UGT1A1 genotype frequencies in HD patients were 49.2%, 42.4%, and 8.4% for 6/6, 6/7, and 7/7 genotypes, respectively. Although no difference was found in UGT1A1 genotype distribution between the three tertiles of bilirubin, significant differences were found with increasing bilirubin levels, namely, a decrease in platelet, leukocyte, and lymphocyte counts, transferrin, oxidized low-density lipoprotein (ox-LDL), ox-LDL/low-density lipoprotein cholesterol ratio, apolipoprotein (Apo) A, Apo B, and interleukin-6 serum levels and a significant increased concentration of hemoglobin, hematocrit, erythrocyte count, iron, transferrin saturation, Apo A/Apo B ratio, adiponectin, and paraoxonase 1 serum levels. After adjustment for age these results remained significant. Our data suggest that higher bilirubin levels are associated with beneficial effects in HD patients, by improving lipid profile and reducing the inflammatory grade, which might contribute to increase in iron availability. These results suggest a potential cardiovascular risk protection of bilirubin in HD patients.

Body fat percentage is a major determinant of total bilirubin independently of UGT1A1*28 polymorphism in young obese

Objectives

Bilirubin has potential antioxidant and anti-inflammatory properties. The UGT1A1*28 polymorphism (TA repeats in the promoter region) is a major determinant of bilirubin levels and recent evidence suggests that raised adiposity may also be a contributing factor. We aimed to study the interaction between UGT1A1 polymorphism, hematological and anthropometric variables with total bilirubin levels in young individuals.

Methods

350 obese (mean age of 11.6 years; 52% females) and 79 controls (mean age of 10.5 years; 59% females) were included. Total bilirubin and C-reactive protein (CRP) plasma levels, hemogram, anthropometric data and UGT1A1 polymorphism were determined. In a subgroup of 74 obese and 40 controls body composition was analyzed by dual-energy X-ray absorptiometry.

Results

The UGT1A1 genotype frequencies were 49.9%, 42.7% and 7.5% for 6/6, 6/7 and 7/7 genotypes, respectively. Patients with 7/7 genotype presented the highest total bilirubin levels, followed by 6/7 and 6/6 genotypes. Compared to controls, obese patients presented higher erythrocyte count, hematocrit, hemoglobin and CRP levels, but no differences in bilirubin or in UGT1A1 genotype distribution. Body fat percentage was inversely correlated with bilirubin in obese patients but not in controls. This inverse association was observed either in 6/7 or 6/6 genotype obese patients. UGT1A1 polymorphism and body fat percentage were the main factors affecting bilirubin levels within obese patients (linear regression analysis).

Conclusion

In obese children and adolescents, body fat composition and UGT1A1 polymorphism are independent determinants of total bilirubin levels. Obese individuals with 6/6 UGT1A1 genotype and higher body fat mass may benefit from a closer clinical follow-up.

Decreased serum bilirubin is associated with arterial stiffness in men

BACKGROUND AND AIMS

The brachial-ankle pulse wave velocity (baPWV) is a marker for early atherosclerotic changes. Serum total bilirubin (TB) is an effective antioxidant and has been associated with carotid intima-media thickness, cardiovascular disease, stroke and peripheral arterial disease, all of which may be caused by arteriosclerosis. This study aimed to investigate the association of TB with arterial stiffness.

METHODS AND RESULTS

In this cross-sectional study, we investigated the relationship between TB and baPWV in 2207 participants (1331 men, 876 women) in a general health examination. Different metabolic parameters were compared across TB quartiles. Age-adjusted mean values of baPWV gradually decreased with TB quartiles in men (Q1 = 1348, Q2 = 1266, Q3 = 1215, and Q4 = 1154 cm/s). However, the age-adjusted means of baPWV had no significance in women according to TB quartiles. Univariate analysis showed that age, smoking status, BMI, SBP, DBP, AST, ALT, GGT, TB, TG, and HDL-C were significantly associated with baPWV in men, whereas only age, BMI, SBP, DBP, TG and FPG were significantly associated with baPWV in women. In addition, BMI, SBP, TB, age, TG, and AST were significant factors in the multivariate model with baPWV in men; only BMI and FPG were significant factors with baPWV in women.

CONCLUSION

The findings show that serum total bilirubin concentration is negatively correlated to arterial stiffness in Chinese men. Early detection of abnormal bilirubin levels could potentially serve as an early biomarker for arterial stiffness.

Can an extended right lobe be harvested from a donor with Gilbert's syndrome for living-donor liver transplantation? Case report

Gilbert's syndrome (GS) is a common cause of inherited benign unconjugated hyperbilirubinemia that occurs in the absence of overt hemolysis, other liver function test abnormalities, and structural liver disease. GS may not affect a patient's selection for living-donor liver transplantation (LDLT). Between February 2005 and April 2011, 446 LDLT procedures were performed at our institution. Two of the 446 living liver donors were diagnosed with GS. Both donors underwent extended right hepatectomies, and donors and recipients experienced no problem in the postoperative period. Their serum bilirubin levels returned to the normal range within 1-2 weeks postoperatively. In our opinion, extended right hepatectomy can be performed safely in living liver donors with GS if appropriate conditions are met and remnant volume is >30%. Livers with GS can be used successfully as grafts in LDLT recipients.

A genome-wide association study of total bilirubin and cholelithiasis risk in sickle cell anemia

Serum bilirubin levels have been associated with polymorphisms in the UGT1A1 promoter in normal populations and in patients with hemolytic anemias, including sickle cell anemia. When hemolysis occurs circulating heme increases, leading to elevated bilirubin levels and an increased incidence of cholelithiasis. We performed the first genome-wide association study (GWAS) of bilirubin levels and cholelithiasis risk in a discovery cohort of 1,117 sickle cell anemia patients. We found 15 single nucleotide polymorphisms (SNPs) associated with total bilirubin levels at the genome-wide significance level (p value <5 × 10(-8)). SNPs in UGT1A1, UGT1A3, UGT1A6, UGT1A8 and UGT1A10, different isoforms within the UGT1A locus, were identified (most significant rs887829, p = 9.08 × 10(-25)). All of these associations were validated in 4 independent sets of sickle cell anemia patients. We tested the association of the 15 SNPs with cholelithiasis in the discovery cohort and found a significant association (most significant p value 1.15 × 10(-4)). These results confirm that the UGT1A region is the major regulator of bilirubin metabolism in African Americans with sickle cell anemia, similar to what is observed in other ethnicities.

Bilirubin dependence on UGT1A1 polymorphisms, hemoglobin, fasting time and body mass index

In humans, bilirubin levels are influenced by different factors. This study evaluates how several nongenetic causes and the genetic UGT1A1 polymorphisms contribute for bilirubin levels, in a cohort of 146 young Caucasian females. Hematological data, bilirubin, screening of TA duplication in the UGT1A1 gene, body mass index (BMI) and body fat were determined. A questionnaire about fasting time, smoking habits, oral contraceptive therapy, caloric intake and physical activity was done. Participants were divided according to the tertiles of bilirubin. Subjects from the second and third tertile had significant rises in hemoglobin (Hb), hematocrit, mean cell Hb and mean cell Hb concentration, and a significant increased frequency for the c.-41_-40dupTA allele in homozygosity, when compared to the first tertile. Red blood cell count was significantly increased in the third tertile. Results showed that the c.-41_-40dupTA allele (genetic), Hb, BMI and fasting time (nongenetic) were the main factors associated bilirubin levels.

Impact of UGT1A1 gene variants on total bilirubin levels in Gilbert syndrome patients and in healthy subjects

The Gilbert syndrome is a benign form of unconjugated hyperbilirubinemia, mainly associated with alterations in UGT1A1 gene. This work investigated the effect of UGT1A1 variants on total bilirubin levels in Gilbert patients (n=45) and healthy controls (n=161). Total bilirubin levels were determined using a colorimetric method; molecular analysis of exons 1-5 and two UGT1A1 promoter regions were performed by direct sequencing and automatic analysis of fragments. Five in silico methods predicted the effect of new identified variants. A significant different allelic distribution, in Gilbert patients and in controls, was found for two promoter polymorphisms. Among patients, 82.2% were homozygous and 17.8% heterozygous for the c.-41_-40dupTA allele; in control group, 9.9% were homozygous and 43.5% heterozygous for this promoter variant, while 46.6% (n=75) presented the [A(TA)6TAA]. For the T>G transition at c.-3279 promoter region, in patients, 86.7% were homozygous and 13.3% heterozygous; in control group, 33.5% were homozygous for the wild type allele, 44.1% were heterozygous and 22.4% homozygous for the mutated allele. The two polymorphisms were in Hardy-Weinberg equilibrium in both groups. Sequencing of UGT1A1 coding region identified nine novel variants, five in patients and four in controls. In silico analysis of these amino acids replacements predicted four of them as benign and three as damaging. In conclusion, we demonstrated that total bilirubin levels are mainly determined by the TA duplication in the TATA-box promoter and by the c.-3279T>G variant. Alterations in the UGT1A1 coding region seem to be associated with increased bilirubin levels, and, therefore, with Gilbert syndrome.

Regulation of sulfotransferase and UDP-glucuronosyltransferase gene expression by the PPARs

During phase II metabolism, a substrate is rendered more hydrophilic through the covalent attachment of an endogenous molecule. The cytosolic sulfotransferase (SULT) and UDP-glucuronosyltransferase (UGT) families of enzymes account for the majority of phase II metabolism in humans and animals. In general, phase II metabolism is considered to be a detoxication process, as sulfate and glucuronide conjugates are more amenable to excretion and elimination than are the parent substrates. However, certain products of phase II metabolism (e.g., unstable sulfate conjugates) are genotoxic. Members of the nuclear receptor superfamily are particularly important regulators of SULT and UGT gene transcription. In metabolically active tissues, increasing evidence supports a major role for lipid-sensing transcription factors, such as peroxisome proliferator-activated receptors (PPARs), in the regulation of rodent and human SULT and UGT gene expression. This review summarizes current information regarding the regulation of these two major classes of phase II metabolizing enzyme by PPARs.

The patient presenting with isolated hyperbilirubinemia

Hyperbilirubinemia is a common laboratory finding in clinical practice, being found in several haematological and liver diseases as well as in familial conditions (5-10% in Western countries). Although most of the familial forms of hyperbilirubinemia are classically viewed as benign conditions, they have gained an increased interest in the last few years since recent data have indicated that subjects with an impaired bilirubin metabolism may have an increased susceptibility to drug toxicity. The authors briefly review the main steps of bilirubin metabolism, with a special emphasis on the emerging concepts on the molecular mechanisms of regulation by nuclear receptors (NRs) and genetic factors. Then the different forms of isolated hyperbilirubinemia occurring in both adults and paediatrics are systematically analysed, and a new categorisation is also proposed in light of the recent advances in bilirubin research. Finally, a diagnostic algorithm is discussed, along with a correct approach to its management, in order to avoid unnecessary medical investigations.

Genome-wide association meta-analysis for total serum bilirubin levels

Variation in serum bilirubin is associated with altered cardiovascular disease risk and drug metabolism. We aimed to identify genetic contributors to variability in serum bilirubin levels by combining results from three genome-wide association studies (Framingham heart study, n = 3424; Rotterdam study, n = 3847; Age, Gene, Environment and Susceptibility-Reykjavik, n = 2193). Meta-analysis showed strong replication for a genetic influence on serum bilirubin levels of the UGT1A1 locus (P < 5 x 10(-324)) and a 12p12.2 locus. The peak signal in the 12p12.2 region was a non-synonymous SNP in SLCO1B1 (rs4149056, P = 6.7 x 10(-13)), which gives rise to a valine to alanine amino acid change leading to reduced activity for a hepatic transporter with known affinity for bilirubin. There were also suggestive associations with several other loci. The top variants in UGT1A1 and SLCO1B1 explain approximately 18.0 and approximately 1.0% of the variation in total serum bilirubin levels, respectively. In a conditional analysis adjusted for individual genotypes for the top UGT1A1 variant, the top SLCO1B1 variant remained highly significant (P = 7.3 x 10(-13)), but no other variants achieved genome-wide significance. In one of the largest genetic studies of bilirubin to date (n = 9464), we confirm the substantial genetic influence of UGT1A1 variants, consistent with past linkage and association studies, and additionally provide strong evidence of a role for allelic variation in SLCO1B1. Given the involvement of bilirubin in a number of physiological and disease processes, and the roles for UGT1A1 and SLCO1B1 in drug metabolism, these genetic findings have potential clinical importance. In analyses for association with gallbladder disease or gallstones, top bilirubin SNPs in UGT1A1 and SLCO1B1 were not associated.

Crigler-Najjar syndrome: therapeutic options and consequences of mutations in the UGT1A1 complex

Crigler-Najjar syndrome (CN), a rare inherited disorder characterized by failure of bilirubin glucuronidation, can lead to severe disability and death from kernicterus. Gilbert syndrome is a more common, benign familial unconjugated hyperbilirubinemia. The underlying problem in both conditions is impaired bilirubin conjugation and elimination due to a mutation in uridine 5'-diphosphate glucuronyltransferase. The mainstay of current management of CN is phototherapy, followed by liver transplantation. Here, we review other therapies, including hepatocyte transplantation, that have been successfully used to lessen the phenotype, although long-term engraftment of cells remains elusive. Gene therapy holds hope for the future whereby the patient's hepatocytes are transduced with the wild-type gene. Outstanding issues include safety of the gene vector and establishing immunotolerance to both vector and the new protein. The significant advances in understanding the relevance of mutations in UGT not only in glucuronidation of bilirubin, but other drugs and substances, are also reviewed.

Gilbert syndrome

Az ismert familiáris, nem konjugált hyperbilirubinaemiák közé tartozó Gilbert-szindróma az átlagpopuláció 7–10%-át érintő benignus kórkép. Tünetei rendszerint aspecifikusak, egyedül az esetlegesen előforduló sárgaság, továbbá az enyhén emelkedett nem konjugált bilirubin szintje utal a rendellenességre. Más laborértékek és a májbiopszia általában nem mutat eltérést a normálistól. A betegség hátterében a legtöbb esetben az UDP-glükuronil-transzferáz gén részleges működészavara áll. A gén azt az enzimet kódolja, amely a bilirubin glükuronsavval való konjugációját segíti. Noha a Gilbert-szindróma diagnosztizálása korábban hagyományos laboratóriumi módszerekkel és családi anamnézis felvételével történt, napjainkban lehetőség van az UDP-glükuronil-transzferáz gén genetikai variánsainak meghatározására. A gén promoterrégiójában, homozigóta formában lévő (TA)-inszerció – (TA)7/(TA)7– a betegek 80–100%-ában jelen van, és az aktív UDP-glükuronil-transzferáz mennyiségének csökkenéséhez vezet. A kódolórégióban található missense mutációk szerepe még nem teljesen tisztázott, de a (TA)7promotervariánssal való együttes előfordulásuk magyarázatul szolgálhat az emelkedett bilirubinszintre és a sárgaságra, valamint a Gilbert-szindróma családi halmozódására.