Coexpression of gene polymorphisms involved in bilirubin production and metabolism

The Genetics of Glucose-6-Phosphate-Dehydrogenase (G6PD) and Uridine Diphosphate Glucuronosyl Transferase 1A1 (UGT1A1) Promoter Gene Polymorphism in Relation to Quantitative Biochemical G6PD Activity Measurement and Neonatal Hyperbilirubinemia

Glucose-6-phosphate dehydrogenase (G6PD) deficiency and polymorphism in uridine diphosphate glucuronosyl transferase 1A1 (UGT1A1) were associated with significant neonatal hyperbilirubinemia (NHB) and increased risk for kernicterus. However, quantitative screening tests for G6PD enzyme activity proved unsatisfactory in estimating the risk for significant NHB, especially in heterozygous females that could present phenotype overlap between normal homozygotes, heterozygotes, and deficient homozygotes, resulting in a continuum of intermediate G6PD activity.

OBJECTIVE

To examine the association of genotype and phenotype in newborns with decreased G6PD activity and its relation to NHB.

STUDY DESIGN

Quantitative G6PD enzyme activities were measured on umbilical cord blood samples. After accepting parental consent, samples were analyzed for G6PD mutations and UGT1A1 gene polymorphisms (number of TA repeats in the UGT1A1 promoter). The associations to quantitative G6PD activity and bilirubin levels were assessed.

RESULTS

28 females and 27 males were studied. The Mediterranean mutation (NM_001360016.2(G6PD): c.563C>T (p.Ser188Phe)) was responsible for most cases of G6PD deficiency (20 hemizygous males, 3 homozygous and 16 heterozygous females). The association between this mutation, decreased G6PD activity and higher bilirubin levels was confirmed. Heterozygosity to 6/7 TA repeats in the UGT1A1 promoter was associated with increased NHB, especially in female newborns with G6PD deficiency. However, it seems that the interaction between G6PD deficiency, UGT1A1 promoter polymorphism, and NHB is more complex, possibly involving other genetic interactions, not yet described. Despite genotyping females with G6PD deficiency, the overlap between the upper range of borderline and the lower range of normal G6PD activity could not be resolved.

CONCLUSIONS

The results of this study highlight the possibility for future implementation of molecular genetic screening to identify infants at risk for significant NHB, especially UGT1A1 polymorphism in heterozygous females with borderline G6PD deficiency. However, further studies are needed before such screening could be applicable to daily practice.

Neonatal hyperbilirubinemia: Background and recent literature updates on the diagnosis and treatment

Hyperbilirubinemia or jaundice has been studied by many researchers because of its diverse causes and potential for toxicity especially in the neonate but to a lesser extent beyond the neonate as well. Several studies have been performed on the normal metabolism and metabolic disorders of bilirubin in last decades of the 20th century. The recent advancement in research and technology facilitated for the researchers to investigate new horizons of the causes and treatment of neonatal hyperbilirubinemia. This review gives a brief introduction to hyperbilirubinemia and jaundice and the recent advancement in the treatment of neonatal hyperbilirubinemia. It reports modifications in the previously used methods and findings of some newly developed ones. At present, ample literature is available discussing the issues regarding hyperbilirubinemia and jaundice, but still more research needs to be done.

Genetic Factors and Delayed TSB Monitoring and Treatment as Risk Factors Associated with Severe Hyperbilirubinemia in Term Neonates Admitted for Phototherapy

OBJECTIVES

This study aimed to determine whether maternal-fetal blood group isoimmunization, breastfeeding, birth trauma, age when first total serum bilirubin (TSB) was measured, age of admission, and genetic predispositions to hemolysis [due to genetic variants of glucose-6-phosphate dehydrogenase (G6PD) enzyme], and reduced hepatic uptake and/or conjugation of serum bilirubin [due to genetic variants of solute carrier organic anion transporter protein family member 1B1 (SLCO1B1) and uridine diphosphate glucuronosyltransferase family 1 member A1 (UGT1A1)] were significant risk factors associated with severe neonatal hyperbilirubinemia (SNH, TSB ≥ 342µmol/l) in jaundiced term neonates admitted for phototherapy.

METHODS

The inclusion criteria were normal term neonates (gestation ≥ 37 weeks). Parents/care-givers were interviewed to obtain data on demography, clinical problems, feeding practice and age when first TSB was measured. Polymerase chain reaction-restriction fragment length polymorphism method was used to detect common G6PD, UGT1A1 and SLCO1B1 variants on each neonate's dry blood specimens.

RESULTS

Of 1121 jaundiced neonates recruited, 232 had SNH. Logistic regression analysis showed that age (in days) when first TSB was measured [adjusted odds ratio (aOR) = 1.395; 95% confidence interval (CI) 1.094-1.779], age (in days) of admission (aOR = 1.127; 95% CI 1.007-1.260) and genetic mutant UGT1A1 promoter A(TA)7TAA (aOR = 4.900; 95% CI 3.103-7.739), UGT1A1 c.686C>A (aOR = 6.095; 95% CI 1.549-23.985), SLCO1B1 c.388G>A (aOR = 1.807; 95% CI 1.242-2.629) and G6PD variants and/or abnormal G6PD screening test (aOR = 2.077; 95% CI 1.025-4.209) were significantly associated with SNH.

CONCLUSION

Genetic predisposition, and delayed measuring first TSB and commencing phototherapy increased risk of SNH.

Molecular Physiology and Pathophysiology of Bilirubin Handling by the Blood, Liver, Intestine, and Brain in the Newborn

Bilirubin is the end product of heme catabolism formed during a process that involves oxidation-reduction reactions and conserves iron body stores. Unconjugated hyperbilirubinemia is common in newborn infants, but rare later in life. The basic physiology of bilirubin metabolism, such as production, transport, and excretion, has been well described. However, in the neonate, numerous variables related to nutrition, ethnicity, and genetic variants at several metabolic steps may be superimposed on the normal physiological hyperbilirubinemia that occurs in the first week of life and results in bilirubin levels that may be toxic to the brain. Bilirubin exists in several isomeric forms that differ in their polarities and is considered a physiologically important antioxidant. Here we review the chemistry of the bilirubin molecule and its metabolism in the body with a particular focus on the processes that impact the newborn infant, and how differences relative to older children and adults contribute to the risk of developing both acute and long-term neurological sequelae in the newborn infant. The final section deals with the interplay between the brain and bilirubin and its entry, clearance, and accumulation. We conclude with a discussion of the current state of knowledge regarding the mechanism(s) of bilirubin neurotoxicity.

Profiling of UGT1A1*6, UGT1A1*60, UGT1A1*93, and UGT1A1*28 Polymorphisms in Indonesian Neonates With Hyperbilirubinemia Using Multiplex PCR Sequencing

Background: Single nucleotide polymorphism (SNP) variants of the uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) gene have been studied as an important factor in neonatal hyperbilirubinemia (jaundice) severity. Specific ethnicities, including Asians, have certain SNPs that appear more frequently than others. Aim: To identify the most common SNPs in Indonesian neonates and their association with the severity of neonatal hyperbilirubinemia. Methods: Eighty-eight inborn and outborn jaundiced infants from three different hospitals (Bengkulu, Jakarta, Biak Papua) across Indonesia were enrolled in this cross-sectional study and their peak total serum bilirubin (TSB) levels assessed. SNP variant analyses of the TATAA box, promoter, and exon 1 regions of UGT1A1 gene from 78 of the 88 infants were carried out using the SNaPshot^R Multiplex Polymerase Chain Reaction (PCR) System followed by DNA sequencing. Results: We detected SNP variants UGT1A1 ^* 28, UGT1A1 ^* 60, UGT1A1 ^* 93, and UGT1A1 ^* 6 in our population. Mean total serum bilirubin (TSB) was 14.59 ± 5.57 mg/dL. Bivariate analyses using delivery location, gestational age, birth weight, mother's age, and ethnicity were shown to be associated with moderate-to-severe hyperbilirubinemia (p < 0.05). None of the four SNPs appeared to be associated with moderate-to-severe hyperbilirubinemia. In multivariate analysis, however, only the "other ethnic group" (e.g., Chinese, Bengkulu, Papua, Bima) category showed an association with moderate-to-severe hyperbilirubinemia, with an odds ratio of 6.49 (95% CI 1.01-41.67; p < 0.05). Conclusions: We found that the UGT1A1 ^* 60 is the most common SNP detected in neonates with hyperbilirubinemia in the Indonesian population. Interestingly, in Indonesia, UGT1A1 polymorphisms do not appear to be associated with differences in the severity of hyperbilirubinemia.

UGT1A1 genotypes and unconjugated hyperbilirubinemia phenotypes in post-neonatal Chinese children: A retrospective analysis and quantitative correlation

To retrospectively analyze and quantitatively correlate UGT1A1 (bilirubin UDP- glucuronosyltransferase gene) genotypes and unconjugated hyperbilirubinemia (UCH) phenotypes among Chinese children.We retrospectively reviewed UCH patients, quantitatively analyzed genotype-phenotype correlation by comparing with healthy controls. Pfam database, SWISS-model, and Pymol were used for UGT1A1 protein domain analysis and protein modeling for assessing the effect of novel missense variants on protein structure.Seventy four cases, including 21 prolonged unconjugated hyperbilirubinemia (PUCH), 30 Gilbert syndrome (GS), 22 Crigler-Najjar syndrome type II (CNS-II), and 1 Crigler-Najjar syndrome type I (CNS-I) phenotypes were analyzed. Total of 21 variants, including 7 novel variants (c.764T>A/p.L255Q, c.1112C>T/p.T371I, c.1028C>A/p.S343X, c.1047delG/p.I350YfsX16, c.996 + 5G>C/g.6923G>C, c.287G>A/p.G96E, and c.1142G>A/p.S381N) were found. In the multiple regression model, heterozygous A(TA)7TAA, G71R/P364L, and Y486D/other mutations were significantly associated with increased risk of GS, PUCH, and CNS-II, respectively. Total allele number is significantly associated with GS and CNS-II, with each increase in total allele number, the odds ratio (OR) of having GS and CNS-II increased by 1.46 and 4.47 fold, respectively. Having only functional polymorphisms in UGT1A1 gene is associated with increased risk of PUCH, and GS with OR values of 5.67 (95% CI: 1.52-21.13), and 3.88 (95% CI: 1.02-14.78), respectively. Having only mutation is associated with significantly increased risk of having GS phenotype (OR: 34.00, 95% CI: 4.65-248.37), but not CNS-II. Polymorphism plus mutation had the strongest association with CNS-II with OR value of 64.80 (95% CI: 7.68-546.41), followed by GS (OR: 4.53, 95% CI: 1.08-19.08).We detected 7 novel variants, and quantitatively calculated risks of having specific phenotypes using genetic data. Among Chinese children, G71R and P364L is independently associated with PUCH, A(TA)7TAA is associated with GS, and Y486D or other disease-causing mutations were associated with CNS-II. Multiple alleles were associated with more severe phenotypes. Combined variant of G71R+Y486D is a common occurrence among Chinese children with UCH.

Correlation between UGT1A1 polymorphism and neonatal hyperbilirubinemia of neonates in Wuhan

This study attempts to discuss the correlation between UGT1A1*28 as uridine diphosphate glucuronosyltransferase gene promoter and coding region Gly71Arg gene polymorphism with neonatal hyperbilirubinemia of neonates in Wuhan. A total of 168 neonates were divided into the hyperbilirubinemia group (case group, n=108) and healthy neonates group (control group, n=60). Their DNA was obtained through blood extraction. The gene exon mutation of UGT1A1 was detected by Sanger sequencing, which revealed the relationship between UGT1A1*28 and Gly71Arg polymorphism with neonatal hyperbilirubinemia of neonates. The results showed that: (1) The frequency of UGT1A1*28 allele mutation in the case group and the control group was 9.3% and 10% respectively, with the difference being not significant between the two groups (P>0.05). (2) The frequency of Gly71Arg allele mutation in the case group and the control group was 35.1% and 21.7% respectively, with the difference being significant between the two groups (P<0.01). (3) The serum bilirubin level of Gly71Arg mutant homozygous and heterozygous subgroups (n=66) in the case group was 302.7±31.4 μmol/L, which was significantly higher than 267.3±28.5 μmol/L of the wild subgroup (n=42) (P<0.01). It was suggested that the occurrence of neonatal hyperbilirubinemia of neonates in Wuhan was not associated with UGT1A1*28 gene polymorphism, but closely with the Gly71Arg gene polymorphism. Meanwhile, the Arg allele mutation was related to the degree of jaundice.

Heme oxygenase-1 promoter polymorphisms: do they modulate neonatal hyperbilirubinemia?

The role of genetic factors in the modulation of serum bilirubin levels and the pathophysiology of neonatal hyperbilirubinemia is being increasingly recognized. Heme oxygenase-1 (HO-1) is the rate-limiting enzyme by which heme is catabolized to biliverdin and thence to bilirubin, with the simultaneous release of equimolar quantities of ferrous iron (Fe³⁺) and carbon monoxide. Polymorphisms of the HO-1 gene promoter may modulate transcriptional activity, thereby augmenting or attenuating HO-1 expression with resultant modulation of the production of bilirubin. Few studies have related these polymorphisms to neonatal bilirubin metabolism and have reported conflicting results. In this clinical review, we surveyed the role of HO-1 gene promoter polymorphisms in the control of bilirubin production and further considered their role, if any, in the pathophysiology of neonatal hyperbilirubinemia.

Evaluation of Neonatal Hemolytic Jaundice: Clinical and Laboratory Parameters

BACKGROUND:

Neonatal jaundice that occurs in ABO or Rhesus issoimunisation has been recognized as one of the major risk factors for development of severe hyperbilirubinemia and bilirubin neurotoxicity.

AIM:

Aim of our study was to investigate clinical and laboratory parameters associated with hemolytic jaundice due to Rh and ABO incompatibility and compare results with the group of unspecific jaundice.

MATERIAL AND METHODS:

One hundred sixty seven (167) neonatal hyperbilirubinemia cases were included in the study, 24.6% of which presented with ABO/Rhesus type hemolytic jaundice, and the rest with unspecific jaundice. Evaluation included: blood count, reticulocites, serum bilirubin, aminotransferases, blood grouping, and Coombs test, also the day of bilirubin peak, duration of the hyperbilirubinemia, and additional bilirubin measurements.

RESULTS:

We showed significantly lower mean values of hemoglobin, erythrocytes and hematocrit and significantly higher values of reticulocytes in the group of ABO/Rh incompatibility compared to the group of jaundice of unspecific etiology; also an earlier presentation and a higher-grade jaundice in this group.

CONCLUSIONS:

The laboratory profile in ABO/Rh isoimmunisation cases depicts hemolytic mechanism of jaundice. These cases carry a significant risk for early and severe hyperbilirubinemia and are eligible for neurodevelopmental follow-up. Hematological parameters and blood grouping are simple diagnostic methods that assist the etiological diagnosis of neonatal hyperbilirubinemia.

Multiple Genetic Modifiers of Bilirubin Metabolism Involvement in Significant Neonatal Hyperbilirubinemia in Patients of Chinese Descent

The potential for genetic variation to modulate neonatal hyperbilirubinemia risk is increasingly being recognized. A case-control study was designed to assess comprehensive contributions of the multiple genetic modifiers of bilirubin metabolism on significant neonatal hyperbilirubinemia in Chinese descendents. Eleven common mutations and polymorphisms across five bilirubin metabolism genes, namely those encoding UGT1A1, HMOX1, BLVRA, SLCO1B1 and SLCO1B3, were determined using the high resolution melt (HRM) assay or PCR-capillary electrophoresis analysis. A total of 129 hyperbilirubinemic infants and 108 control subjects were evaluated. Breastfeeding and the presence of the minor A allele of rs4148323 (UGTA*6) were correlated with an increased risk of hyperbilirubinemia (OR=2.17, P=0.02 for breastfeeding; OR=9.776, P=0.000 for UGTA*6 homozygote; OR=3.151, P=0.000 for UGTA*6 heterozygote); whereas, increasing gestational age and the presence of –TA₇ repeat variant of UGT1A1 decreased the risk (OR=0.721, P=0.003 for gestational age; OR=0.313, P=0.002 for heterozygote TA₆/TA₇). In addition, the SLCO1B1 and SLCO1B3 polymorphisms also contributed to an increased risk of hyperbilirubinemia. This detailed analysis revealed the impact of multiple genetic modifiers on neonatal hyperbilirubinemia. This may support the use of genetic tests for clinical risk assessment. Furthermore, the established HRM assay can serve as an effective method for large-scale investigation.

Prolonged phototherapy needed for a neonate with four mutations in genes involved in bilirubin production and metabolism

We cared for a neonate with hyperbilirubinemia requiring phototherapy during the birth-hospitalization, at home, and during two subsequent hospital readmissions. Abnormal red blood cell forms including elliptocytes were seen on his blood film but this failed to explain, to our satisfaction, why his jaundice required such prolonged treatment. Next-generation sequencing, using a panel of 27 genes involved in neonatal jaundice and hemolytic anemia revealed four previously described heterozygous variations, which we postulate resulted in increased bilirubin production from hemolysis, plus retarded bilirubin uptake and conjugation. Mutations were found in the erythrocyte membrane protein band 4.1 gene (EPB41), the alpha-spectrin gene (SPTA1), the gene encoding the enzyme for bilirubin conjugation (UGT1A1), and the gene encoding a transporter of bilirubin from the blood into hepatocytes (SLCO1B1).

Glucose-6-phosphate-dehydrogenase deficiency and its correlation with other risk factors in jaundiced newborns in Southern Brazil

OBJECTIVE

To evaluate the correlation between glucose-6-phosphate-dehydrogenase (G6PD) deficiency and neonatal jaundice.

METHODS

Prospective, observational case-control study was conducted on 490 newborns admitted to Hospital de Clínicas de Porto Alegre for phototherapy, who all experienced 35 or more weeks of gestation, from March to December 2007. Enzymatic screening of G6PD activity was performed, followed by PCR.

RESULTS

There was prevalence of 4.6% and a boy-girl ratio of 3:1 in jaundiced newborns. No jaundiced neonate with ABO incompatibility presented G6PD deficiency, and no Mediterranean mutation was found. A higher proportion of deficiency was observed in Afro-descendants. There was no association with UGT1A1 variants.

CONCLUSIONS

G6PD deficiency is not related to severe hyperbilirubinemia and considering the high miscegenation in this area of Brazil, other gene interactions should be investigated.

Causes of hemolysis in neonates with extreme hyperbilirubinemia

OBJECTIVE

We instituted a quality improvement process to enhance our capacity to diagnose genetic hemolytic conditions in neonates with extreme hyperbilirubinemia.

STUDY DESIGN

During a 1-year period, whenever the total serum bilirubin (TSB) was >25 mg dl(-1) a special evaluation was performed. If we deemed an erythrocyte membrane defect likely, based on red blood cell morphology, EMA-flow cytometry was performed. Otherwise 'next-generation' sequencing was performed using a panel of genes involved in neonatal hyperbilirubinemia.

RESULT

Ten neonates had a TSB ⩾ 25 mg dl(-1). Two others were evaluated as part of this process at the request of their attending neonatologists, because each had a TSB >14 mg dl(-1) in the first hours after birth and required phototherapy for ⩾ 1 week. Explanations for the jaundice were found in all 12 neonates. Five had hereditary spherocytosis, three of which also had ABO hemolytic disease. Two had pyruvate kinase deficiency. One had severe G6PD deficiency. The other four had ABO hemolytic disease.

CONCLUSION

On the basis of the present small case series, we suggest that among neonates with extreme hyperbilirubinemia, it can be productive to pursue a genetic basis for hemolytic disease.

Prevention of Kernicterus in South Asia: role of neonatal G6PD deficiency and its identification

Extreme hyperbilirubinemia (EHB) caused by neonatal glucose-6-phosphate dehydrogenase (G6PD) deficiency is strongly associated with mortality and long-term neurodevelopmental impairment, yet there are limited national strategies to reduce this burden in South Asia. Current known and predicted prevalence of G6PD deficiency in Afghanistan, Bangladesh, Bhutan, India, Nepal, and Pakistan ranges from 3.8 to 15 %, with regional "hot spots" exceeding 22 %. Annually, 3.14 million infants are born at risk for this condition. In 2010, South Asian countries reported 37 million (27 %) of world-wide livebirths ≥ 32 wk gestational-age and G6PD deficiency accounted for > 33 % of the global EHB burden, in contrast to 2.2 % for those born in high-income nations. Traditional national approach includes universal newborn screening in malaria-endemic countries or those with prevalence >3.5 %. However, screening implementation should be best optimized using timely quantitative enzyme assay and identification of at-risk female newborns. Furthermore, economic and social constraints, in context of sub-regional variances, call for flexible problem-solving methods in anticipation of changing community demographics. Thus, incremental and need-based newborn screening programs could be the most optimal approach. A human-centered design (HCD) approach, as an alternate pathway, could build the evidence to translate the complex biology of G6PD deficiency and the biodesign of affordable technologies, allowing facilitation of access to knowledge and services, in order to deliver on a long-term public health mandate. Key steps would encompass the initiation of local inquiry of both quantitative and qualitative data to identify at-risk communities and to prospectively design for local innovative solutions.

Relation between Neonatal Icter and Gilbert Syndrome in Gloucose-6-Phosphate Dehydrogenase Deficient Subjects

BACKGROUND AND AIM

The pathogenesis of neonatal hyperbilirubinemia hasn't been completely defined in Gloucose-6-Phosphate Dehydrogenase (G6PD) deficient newborns. The aim of this study was to detect the relationship between Gilbert's syndrome and hyperbilirubinemia in Gloucose-6-Phosphate Dehydrogenase (G6PD) deficient neonates.

MATERIALS AND METHODS

This case-control study was conducted in Amirkola pediatrics teaching hospital, Babol, Iran. A total number of one hundred four infants were included in the study (51 infants with neonatal jaundice and Gloucose-6-Phosphate Dehydrogenase (G6PD) deficiency admitted to phototherapy or transfusion were selected as the case group and 53 infants with Gloucose-6-Phosphate Dehydrogenase (G6PD) deficiency admitted for other reasons than jaundice were selected as the control group). Exclusion criteria were ABO or Rh incompatibility or other reasons that made Coombs test positive, sepsis, hepatosplenomegaly, metabolic diseases, medical treatment and phototherapy. The promoter and coding regions of Uridine diphosphate Glucuronosyl Transferase 1A1 (UGT1A1) of genomic DNA were amplified by polymerase chain reaction (PCR) isolated from leukocytes. We used chi-square test and t-test to compare cases and controls.

RESULTS

Distribution of Gilbert genome was not significantly different between the two groups; among cases, 33.3% were homozygote, 35.3% heterozygote, and 31.4% normal. Among controls, 22.6% were homozygote, 34% heterozygote, and 43.4% normal (p-value=xxx). Hyperbilirubinemia family history didn't differ significantly between these two groups.

CONCLUSIONS

We showed that in Gloucose-6-Phosphate Dehydrogenase (G6PD) deficient neonates, there was no significant association between Gilbert's syndrome (promoter polymorphism) and hyperbilirubinemia.

In vitro OATP1B1 and OATP1B3 inhibition is associated with observations of benign clinical unconjugated hyperbilirubinemia

1.  Transient benign unconjugated hyperbilirubinemia has been observed clinically with several drugs including indinavir, cyclosporine, and rifamycin SV. Genome-wide association studies have shown significant association of OATP1B1 and UGT1A1 with elevations of unconjugated bilirubin, and OATP1B1 inhibition data correlated with clinical unconjugated hyperbilirubinemia for several compounds. 2.  In this study, inhibition of OATP1B3 and UGT1A1, in addition to OATP1B1, was explored to determine whether one measure offers value over the other as a potential prospective tool to predict unconjugated hyperbilirubinemia. OATP1B1 and OATP1B3-mediated transport of bilirubin was confirmed and inhibition was determined for atazanavir, rifampicin, indinavir, amprenavir, cyclosporine, rifamycin SV and saquinavir. To investigate the intrinsic inhibition by the drugs, both in vivo Fi (fraction of intrinsic inhibition) and R-value (estimated maximum in vivo inhibition) for OATP1B1, OATP1B3 and UGT1A1 were calculated. 3.  The results indicated that in vivo Fi values >0.2 or R-values >1.5 for OATP1B1 or OATP1B3, but not UGT1A1, are associated with previously reported clinical cases of drug-induced unconjugated hyperbilirubinemia. 4.  In conclusion, inhibition of OATP1B1 and/or OATP1B3 along with predicted human pharmacokinetic data could be used pre-clinically to predict potential drug-induced benign unconjugated hyperbilirubinemia in the clinic.

UGT1A1 genetic analysis as a diagnostic aid for individuals with unconjugated hyperbilirubinemia

OBJECTIVE

To assess the clinical utility of UGT1A1 genetic testing and describe the spectrum and prevalence of UGT1A1 variations identified in pediatric unconjugated hyperbilirubinemia (UCH), and to characterize specific genotype-phenotype relationships in suspected Gilbert and Crigler-Najjar syndromes.

STUDY DESIGN

A retrospective study was conducted to review clinical information and UGT1A1 genotyping data from 181 pediatric patients referred for UCH. In silico analyses were performed to aid in the assessment of novel UGT1A1 variants.

RESULTS

Overall, 146/181 pediatric patients had at least one heterozygous UGT1A1 functional variant. Identified UGT1A1 variants included 17 novel variants, 7 rare star alleles, and 1 rare variant. There were 129 individuals who possessed the TA7 (*28) promoter repeat and 15 individuals who possessed the *6 (c.211G > A) variation. Out of the 104 individuals with accompanying bilirubin levels, 41 individuals did not have identifiable UGT1A1 variants that explained their UCH, although glucose-6-phosphate dehydrogenase deficiency and other causes of UCH could not be ruled out.

CONCLUSION

Much of the observed UCH could be attributed to variation at the UGT1A1 locus, and UGT1A1 testing helped to substantiate a genetic diagnosis, thereby aiding in individual and family disease management. Although UGT1A1 variation plays a large role in UCH, genetic assessment of UGT1A1 alone may not be comprehensive. Assessment of additional genes may also be useful to evaluate genetic causes for UCH.

Unexplained extreme hyperbilirubinemia among neonates in a multihospital healthcare system

We report a series of neonates who developed a total serum bilirubin (TSB) >20mg/dL during a recent ten-year period in a multihospital healthcare system. The incidence of a TSB >20mg/dL fell after instituting a pre-hospital discharge bilirubin screening program in 2003/2004 (91.3 cases/10,000 births before vs. 72.4/10,000 after), but the incidence has subsequently remained unchanged. No specific cause for the hyperbilirubinemia was identified in 66% of (n=32) cases with a TSB >30 mg/dL or in 76% of (n=112) cases with a TSB 25.0-29.9 mg/dL. We hypothesized that hemolysis was a common contributing mechanism, but our review of hospital records indicated that in most instances these infants were not evaluated sufficiently to test this hypothesis. Records review showed maternal and neonatal blood types and direct antiglobulin testing were performed in >95% cases, but rarely were other tests for hemolysis obtained. In the ten-year period reviewed there were zero instances where erythrocyte morphology from a blood film examination or Heinz body evaluation by a pediatric hematologist or pathologist were performed. In 3% of cases pyruvate kinase was tested, 3% were evaluated by hemoglobin electrophoresis, 3% had a haptoglobin measurement, and 16% were tested for G6PD deficiency. Thus, determining the cause for hyperbilirubinemia in neonates remains a problem at Intermountain Healthcare and, we submit, elsewhere. As a result, the majority of infants with a TSB >25mg/dL have no specific causation identified. We speculate that most of these cases involve hemolysis and that the etiology could be identified if searched for more systematically. With this in mind, we propose a "consistent approach" to evaluating the cause(s) of hyperbilirubinemia among neonates with a TSB >25mg/dL.

Risk of hyperbilirubinemia in breast-fed infants

OBJECTIVE

To investigate the risk factors for hyperbilirubinemia in infants who are exclusively breast-fed.

STUDY DESIGN

A prospective study was conducted to investigate the effects of birth body weight, sex, mode of delivery, glucose-6-phosphate dehydrogenase (G6PD) deficiency, variant UDP-glucuronosyltransferase 1A1 (UGT1A1) gene, and hepatic solute carrier organic anion transporter 1B1 (SLCO1B1) gene on hyperbilirubinemia in neonates who were breast-fed. Hyperbilirubinemia was diagnosed when a full term neonate had a bilirubin level ≧15.0 mg/dL (256.5 μM) in serum at 3 days old. The polymerase chain reaction-restriction fragment length polymorphism method was used as a means of detecting the known variant sites in the UGT1A1 and SLCO1B1 gene.

RESULTS

Of 252 infants born at term who were exclusively breast-fed, 59 (23.4%) had hyperbilirubinemia. The significant risk factors were a variant nucleotide 211 in UGT1A1 (2.48; 95% CI, 1.29 to 4.76; P = .006), G6PD deficiency (12.24; 95% CI, 1.08 to 138.62; P < .05), and vaginal delivery (3.55; 95% CI, 1.64 to 7.66; P < .001).

CONCLUSION

Breast-fed neonates who are 211 variants in the UGT1A1, G6PD deficiency, and vaginal delivery are at high-risk for hyperbilirubinemia.

211 G to a variation of UDP-glucuronosyl transferase 1A1 gene and neonatal breastfeeding jaundice

Breastfeeding jaundice is a common problem in neonates who were exclusively breastfed, but its pathogenesis is still unclear. The uridine diphosphate glucuronosyl transferase 1A1 (UGT1A1) gene polymorphism was shown to contribute to the development of neonatal hyperbilirubinemia. We hypothesize that the variation of UGT1A1 gene may contribute to neonatal breastfeeding jaundice. We prospectively enrolled 688 near-term and term infants who were exclusively breastfed (BF group) or were supplemented by infant formula partially (SF group) before onset of hyperbilirubinemia. Genotyping of the promoter and exon1 of UGT1A1 was performed in all neonates. Neonates in BF group had a significantly higher maximal body weight loss ratio, peak bilirubin level, and a greater incidence of hyperbilirubinemia than those in SF group. Neonates with nucleotide 211 GA or AA variation in UGT1A1 genotypes had higher peak serum bilirubin levels and higher incidence of hyperbilirubinemia than WTs (GG). This phenomenon was only seen in BF group but not in SF group when subset analysis was performed. This suggests that neonates who carry the nucleotide 211 GA or AA variation within coding region in UGT1A1 gene are more susceptible to develop early-onset neonatal breastfeeding jaundice.

Clinical and genetic risk factors for moderate hyperbilirubinemia in Brazilian newborn infants

OBJECTIVE

To identify clinical and genetic risk factors for moderate hyperbilirubinemia during the first week of life.

STUDY DESIGN

Using univariate and multivariate multiple regression analyses, the RR for clinical factors, the African variant of glucose-6-phosphate dehydrogenase (G6PD) deficiency (G202A/A376G), and (TA)(n) UGT1A1 polymorphisms were established in a cohort of 608 Brazilian newborn infants. Hyperbilirubinemia was monitored until 134.5 ± 49.8 h of life (IQR, 111.0 to 156.7). The dependent variable was total bilirubinemia (TB) ≥12.9 mg per 100 ml estimated by transcutaneous or plasma bilirubin measurements.

RESULT

The African variant of G6PD deficiency and (TA)(7)/(TA)(7) and (TA)(7)/(TA)(8) polymorphisms present in 6.1 and 12.0% of newborns, respectively, were not risk factors for moderate hyperbilirubinemia. Coexpression of G6DP deficiency and UGT1A1 polymorphisms occurred in 0.49% of the subjects. Independent clinical predictors for TB≥ 12.9 mg per 100 ml were gestational age <38 weeks and reference curve percentiles >P40th.

CONCLUSION

In this study, G6PD deficiency and UGT1A1 gene promoter polymorphisms were not risk factors for moderate hyperbilirubinemia. Genetic factors may vary considerably in importance among different populations.

Polymorphic variants of UGT1A1 in neonatal jaundice in southern Brazil

Alterations in the hepatic conjugation of bilirubin due to uridyl-diphosphate-glucuronosyltransferase 1A1 (UGT1A1) polymorphisms have been proposed as risk factors to neonatal jaundice. Herein, we estimated the frequency of genotypes of the promoter region of UGT1A1 gene in newborns and evaluated its association with severe hyperbilirubinemia. Prospective study of cases and controls including all newborns admitted for phototherapy at HCPA, Brazil, during 9 months; 490 babies were enrolled and PCR was performed. Polymorphic genotypes were detected in 16% of the patients and 7 of the 10 possible genotypes were identified with higher prevalence of polymorphisms in Afro-descendants. In this sample, the variants of UGT1A1 were not associated to severe hyperbilirubinemia; other genic factors should be sought in this high miscegenation area of Brazil.

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.

Metalloporphyrins in the management of neonatal hyperbilirubinemia

Neonatal jaundice in the first week of life is a common problem in newborns. It is due to an imbalance of bilirubin production and its elimination, which can lead to significantly elevated levels of circulating bilirubin or hyperbilirubinemia. Use of phototherapy and/or exchange transfusion are the current modes for treating neonatal hyperbilirubinemia and preventing any neurologic damage. These strategies, however, only remove bilirubin that has already been formed. Preventing the production of excess bilirubin may be a more logical approach. Synthetic heme analogs, metalloporphyrins, are competitive inhibitors of heme oxygenase, the rate-limiting enzyme in bilirubin production, and their use has been proposed as an attractive alternative strategy for preventing or treating severe hyperbilirubinemia.

Exploring the genetic architecture of neonatal hyperbilirubinemia

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

Glucose-6-phosphate dehydrogenase deficiency and severe neonatal hyperbilirubinemia: a complexity of interactions between genes and environment

Glucose-6-phosphate dehydrogenase deficiency is a commonly occurring genetic condition, likely to be encountered today in virtually any corner of the globe. Sudden episodes of hemolysis associated with the condition may result in exponential increases in serum total bilirubin concentrations to levels at which bilirubin-induced neurologic damage may occur. The hyperbilirubinemia is the result of complex interactions between genes and environment. Neonatal screening programs coupled with parental and medical caretaker education may be successful in limiting the severity of disease.

Understanding neonatal jaundice: a perspective on causation

Neonatal jaundice can be best understood as a balance between the production and elimination of bilirubin, with a multitude of factors and conditions affecting each of these processes. When an imbalance results because of an increase in circulating bilirubin (or the bilirubin load) to significantly high levels (severe hyperbilirubinemia), it may cause permanent neurologic sequelae (kernicterus). In most infants, an increase in bilirubin production (e.g., due to hemolysis) is the primary cause of severe hyperbilirubinemia, and thus reducing bilirubin production is a rational approach for its management. The situation can become critical in infants with an associated impaired bilirubin elimination mechanism as a result of a genetic deficiency and/or polymorphism. Combining information about bilirubin production and genetic information about bilirubin elimination with the tracking of bilirubin levels means that a relative assessment of jaundice risk might be feasible. Information on the level of bilirubin production and its rate of elimination may help to guide the clinical management of neonatal jaundice.

Hyperbilirubinemia in African American neonates: clinical issues and current challenges

African American neonates evidence a low incidence of hyperbilirubinemia yet account for more than 25% of the reported kernicterus cases in the USA. Glucose-6-phosphate dehydrogenase (G6PD) deficiency accounts for approximately 60%, and late preterm gestation and ABO hemolytic disease approximately 40% of these cases. Females heterozygous for G6PD A- harbor a population of G6PD-deficient red blood cells and are at risk for hyperbilirubinemia. Pre-discharge bilirubin measurement coupled with gestational age enhances the identification of neonates at hyperbilirubinemia risk. Parental education at the time of birth hospitalization discharge combined with timely follow-up may help to reduce the risk of developing hazardous hyperbilirubinemia.

In vivo glucuronidation activity of drugs in neonates: extensive interindividual variability despite their young age

Compared with phase I isoenzymes, data on isoenzyme-specific phenotypic activity of uridine diphosphate glucuronosyltransferase (UGT) and its covariates in neonates are limited. In vivo observations on morphine, paracetamol (acetaminophen), and propofol disposition throughout childhood confirm the overall low-glucuronidation activity in neonates observed in in vitro studies. In addition to the phenotypic low-glucuronidation activity, in vivo observations of bilirubin (UGT1A1), morphine (UGT2B7), paracetamol (UGT1A6), and propofol (UGT1A9) glucuronidation in neonates display extensive interindividual variability, only in part explained by postmenstrual and postnatal age. Covariates like disease state characteristics (decreased morphine metabolism during therapeutic head cooling), genetic polymorphisms (UGT1A1 genetic variants and differences in bilirubin metabolism), or environmental factors (increased urinary excretion of paracetamol-glucuronide by repeated administration of paracetamol) further contribute to this variability. A focused approach to unveil covariates of the interindividual range is needed to improve our knowledge on drug disposition in early life.

Complex multifactorial nature of significant hyperbilirubinemia in neonates

OBJECTIVE

To determine whether glucose-6-phosphate dehydrogenase (G6PD), uridine-diphosphoglucuronosyltransferase 1A1 (UGT1A1), and hepatic solute carrier organic anion transporter 1B1 (SLCO1B1) gene variants occur at greater frequency in neonates with significant hyperbilirubinemia.

METHODS

Infants with gestational ages of >or=37 weeks and ages of <7 days were studied. Case subjects had >or=1 bilirubin level above the 95th percentile (high-risk zone), whereas control subjects had bilirubin levels of <40th percentile (low-risk zone) at study entry.

RESULTS

A total of 153 case subjects (median bilirubin level: 15.7 mg/dL) and 299 control subjects (median bilirubin level: 4.6 mg/dL) were evaluated. There were no statistical differences in the frequencies of G6PD, UGT1A1, and SCLO1B1 gene variants between case and control subjects (G6PD: 5.2% vs 3.3%; UGT1A1: 14.4% vs 9.4%; SLCO1B1: 73.2% vs 73.6%). However, coexpression of the G6PD African A- mutation with UGT1A1 and/or SLCO1B1 variants was seen more frequently for case subjects. Case subjects more often demonstrated >or=2 factors contributing to hyperbilirubinemia, including ABO blood group heterospecificity in which the mother had blood group O (47.7% vs 11.4%), positive direct Coombs test results (33.3% vs 4%), sibling treated with phototherapy (16.3% vs 5.4%), maternal circulating blood group antibodies (10.5 vs 0.7%), maternal diabetes mellitus (13.1% vs 6.4%), and maternal East Asian ethnicity (6.5% vs 1.3%).

CONCLUSIONS

Clinical contributors to hyperbilirubinemia were identified more frequently for case subjects but individually G6PD, UGT1A1, and SLCO1B1 variants were not. Coexpression of the G6PD African A- mutation with UGT1A1 and SLCO1B1 variants was seen more often for case subjects.

Reversibility of acute intermediate phase bilirubin encephalopathy

AIM

To show the potential for reversing acute intermediate to advanced phase bilirubin encephalopathy.

METHODS

Case studies.

RESULTS

Six extremely jaundiced infants had symptoms of intermediate to advanced phase acute bilirubin encephalopathy. The infants were treated aggressively. Two patients had brain magnetic resonance imaging showing increased signals in the globus pallidus. On follow-up, all infants are neurologically normal.

CONCLUSIONS

Intermediate-to-advanced stage acute bilirubin encephalopathy may occasionally be reversible. These cases provide a strong argument in favour of rapid and aggressive intervention in infants presenting with extreme jaundice and neurological symptoms.

Conditional linkage and genome-wide association studies identify UGT1A1 as a major gene for anti-atherogenic serum bilirubin levels--the Framingham Heart Study

OBJECTIVE AND METHODS

Low bilirubin levels are significantly associated with cardiovascular diseases (CVD). In previous genome-wide linkage studies we identified a major locus on chromosome 2q harboring the candidate gene UDP-glucuronosyltransferase (UGT1A1). The activity of this enzyme is significantly influenced by a TA-repeat polymorphism in the promoter of the gene. In a prospective study individuals with genotype (TA)7/(TA)7 had significantly higher bilirubin levels and approximately one-third the risk of CVD as carriers of the wildtype (TA)6 allele. In the present study we performed a conditional linkage study to investigate whether this polymorphism explains the observed linkage peak and extended our analysis by a genome-wide association study on bilirubin levels in 1345 individuals.

RESULTS

After adjustment for the bilirubin variance explained by this polymorphism, the LOD score on chromosome 2q dropped from 3.8 to 0.4, demonstrating that this polymorphism explains the previous linkage result. For the genome-wide association study, the closest marker to UGT1A1 was in the top ranking SNPs. The association became even stronger when we considered the TA-repeat polymorphism in the analysis (p=2.68 x 10(-53)). Five other SNPs in other regions reached genome-wide significance without obvious connection to bilirubin metabolism.

CONCLUSIONS

Our studies suggest that UGT1A1 may be the major gene with strong effects on bilirubin levels and the TA-repeat polymorphism might be the key polymorphism within the gene controlling bilirubin levels. Since this polymorphism has a high frequency and a substantial impact on the development of CVD, the gene might be an important drug target.