Bilirubin genetics for the nongeneticist: hereditary defects of neonatal bilirubin conjugation

Is it time for a precision health approach to the management of newborn hyperbilirubinemia?

Newborn hyperbilirubinemia during the first two weeks of life is one of most common problems requiring management decisions by a pediatrician. However, high bilirubin levels in the circulation have been associated with neurologic injury under a variety of conditions encountered in the newborn infant, such as hemolysis. The risk for developing dangerous hyperbilirubinemia is multifactorial and is determined by a complex set of factors related to a newborn infant's genetic capacities as well as intra- and extrauterine exposures. To this end, a precision health approach based on the integration of prenatal genetic and postnatal diagnostic measures might improve the management of neonatal hyperbilirubinemia.

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.

Dependence of blood biochemical parameters on various genotypes of the UGT1A1 gene associated with gilbert's syndrome

Diagnosis of Gilbert's syndrome is based on the detection of homozygous carriage of an additional TA-repeat in the promoter of the UGT1A1 gene, leading to a decrease in the activity of the UGT enzyme. No large studies have been done in the Russian Federation on the prevalence of carriage of Gilbert's syndrome, as well as the biochemical and molecular profile of such patients. The aim of the study is to evaluate biochemical and molecular genetic parameters in patients with Gilbert's syndrome in Russia. The study included 124 healthy volunteers (group 1) and 5650 patients with suspected Gilbert's syndrome (group 2). The number of TA-repeats of the promoter region of the UGT1A1 gene was determined by the method of fragment analysis for all participants. The following biochemical parameters were analyzed for 299 patients from group 2: the level of bilirubin and its fractions, AST, ALT, cholesterol and LDL. In group 1 the prevalence of genotype (TA)6/(TA)6 was 39,52%, (TA)6/(TA)7 - 53,23%, (TA)7/(TA)7 - 7,26%, no rare forms were found. In group 2 the prevalence of genotype (TA)6/(TA)6 was 6,04%, (TA)6/(TA)7 - 20,05%, (TA)7/(TA)7 - 73,7%, rare alleles - 0,2%. Rare alleles included (TA)5/(TA)6, (TA)5/(TA)7, (TA)6/(TA)8 and (TA)7/(TA)8, as well as a new genotype not described in the literature previously - (TA)7/(TA)9. When assessing the level of total bilirubin and its fractions, a difference was revealed between the genotype of Gilbert's syndrome (TA)7/(TA)7 and the reference genotype (TA)6/(TA)6, and between genotypes (TA)7/(TA)7 and (TA)6/(TA)7. A significant increase in total bilirubin was demonstrated in carriers of a larger number of TA-repeats. There was no significant difference in the concentration of ALT, AST, cholesterol or LDL between different genotypes.The number of TA-repeats of the UGT1A1 gene affects the increase of total bilirubin and its indirect fraction, including the cases of rare allelic variants (TA≤5, TA≥8), but not the activity of ALT and AST and the lipid profile.

The relationship between hyperbilirubinemia and the promoter region and first exon of UGT1A1 gene polymorphisms in Vietnamese newborns

BACKGROUND

To investigate the relationship between unexplained indirect hyperbilirubinemia of Vietnamese newborns and the polymorphism of the promoter TATA box and exon 1 of bilirubin uridine diphosphate glucuronosyltransferase (UGT1A1) gene.

METHODS

A total of 149 neonates were divided into the hyperbilirubinemia group (n = 99) and control group (n = 50). The gene polymorphisms of UGT1A1 gene in the two groups were detected by PCR and direct sequencing, which revealed the relationship between UGT1A1 polymorphism with neonatal hyperbilirubinemia of neonates. The types of UGT1A1 polymorphism in the hyperbilirubinemia group and the peak total serum bilirubin (PSB) levels with different genotypes were observed.

RESULTS

(1) (TA)7 insertion mutation, 211G>A, 189C>T, 190G>A, 378C>T and 686C>A were detected. (2) The allele frequency of 211G>A allele mutation was significantly different between the two groups (p < 0.05). (3) Logistic regression analysis showed that homozygosity and heterozygosity of 211G>A were both significantly associated with neonatal hyperbilirubinemia. (4) In the hyperbilirubinemia group, the peak total serum bilirubin level of 211G>A homozygous neonates was higher than that of the wild-type neonates (p < 0.05).

CONCLUSIONS

We noted that there was an association between neonates with unexplained indirect hyperbilirubinemia in Vietnam and the polymorphism of UGT1A1c.211G>A. In addition, the homozygous 211G>A polymorphism was related to the degree of hyperbilirubinemia.

IMPACT

Our article provided data on UGT1A1 polymorphism distribution in the Vietnamese population, which have not been reported yet. Our findings revealed that mutations in UGT1A1 gene are risk factors for unexplained hyperbilirubinemia in Vietnamese neonates. Our article will strengthen the cognition of neonatal jaundice at the genetic level in the pediatric field in Vietnam.

The role of UGT1A1 (c.-3279 T > G) gene polymorphisms in neonatal hyperbilirubinemia susceptibility

Background

Neonatal hyperbilirubinemia (NNH) is a common disease in newborns. This research study aimed to assess the associations between uridine diphospho-glucuronate-glucuronosyltransferase 1A1 (UGT1A1, c.-3279 T > G) polymorphisms and NNH risk.

Methods

We searched PubMed, the Cochrane Library, and the Embase electronic databases. All published eligible studies before July 1, 2019, were searched for this meta-analysis.

Results

We identified 7 independent studies including 1560 cases. The data showed that in the general population, compared with the GT + GG vs TT and GG vs TT, c.-3279 T > G (rs4124874) was significantly related to a higher NNH risk (GG vs TT: OR = 1.865, 95% CI: 1.031–3.373, P = 0.039; GT + GG vs TT: OR = 1.331, 95% CI: 1.055–1.679, P = 0.016). Although not statistically significant, the data showed that c.3279 T > G had a tendency to be associated with NNH under the allele model and GG vs GT + TT in the overall population (G vs T: OR = 1.288, 95% CI: 0.982–1.689, P = 0.067; GG vs TT + GT: OR = 1.583, 95% CI: 0.947–2.647, P = 0.080).

Conclusion

The UGT1A1 gene c.-3279 T > G (rs4124874) polymorphism increased susceptibility to NNH, especially for the comparison of GT + GG vs TT and GG vs TT. In the future, we can use homozygous state of the UGT1A1 gene c.-3279 T > G (rs4124874) polymorphism for the diagnosis and screening of molecular biomarkers in NNH patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12881-020-01155-2.

Uridine 5'-diphospho-glucronosyltrasferase: Its role in pharmacogenomics and human disease

Biotransformation is an enzyme-catalyzed process in which the body converts endogenous compounds, xenobiotics and toxic substances into harmless or easily excreted metabolites. The biotransformation reactions are classified as phase I and II reactions. Uridine 5'-diphospho (UDP)-glucuronosyltransferases (UGTs) are a superfamily of phase II enzymes which have roles in the conjugation of xenobiotics or endogenous compounds, including drugs and bilirubin, with glucuronic acid to make them easier to excrete. The method the human body uses to achieve glucuronidation may be affected by a large interindividual variation due to changes in the sequences of the genes encoding these enzymes. In the last five years, the study of the genetic variants of the UGTs at a molecular level has become important due to its association with several diseases and the ability to predict adverse events due to drug metabolism. In the present review, the structure and the prominent genetic variants of the UGT1A subfamily and their metabolic and clinical implications are described.

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.

Correlations between polymorphisms in the uridine diphosphate-glucuronosyltransferase 1A and C-C motif chemokine receptor 5 genes and infection with the hepatitis B virus in three ethnic groups in China

Objective

To determine whether genetic polymorphisms in the uridine diphosphate-glucuronosyltransferase 1A (UGT1A) and the C-C motif chemokine receptor 5 (CCR5) genes are associated with hepatitis B virus (HBV) infection in Yi, Yao and Han ethnic groups in the Guizhou Province of China.

Methods

The study enrolled subjects with and without HBV infection. Whole blood was used for DNA genotyping using standard techniques. The study determined the frequencies of several polymorphic alleles (UGT1A6 [rs2070959], UGT1A1 [rs8175347], CCR5-59029 [rs1799987] and CCR5Δ32 [rs333]) and then characterized their relationship with HBV infection.

Results

A total of 404 subjects were enrolled in the study: 138 from the Yao group, 101 from the Yi group and 165 from the Han group. There was a significant difference in the frequency of UGT1A1 rs8175347 polymorphisms among the three groups. The rates of 7TA carriers of UGT1A1 rs8175347 in all three groups were significantly higher than the other genotypes. Individuals with genotype AA of UGT1A6 rs2070959 in the Yi group had a higher risk for HBV infection than in the Yao and Han groups. The frequency of genotype GG in CCR5-59029 in the Yao group was significantly higher than in the Yi group. The genotypes of CCR5Δ32 were not associated with HBV infection.

Conclusion

These findings provide genetic and epidemiological evidence for an association of UGT1A and CCR5-59029 polymorphisms with HBV infection in Chinese Yi and Yao populations.

The role of UGT1A1 promoter polymorphism and exon-1 mutations in neonatal jaundice

OBJECTIVE

In the present study, we investigated the effects of promoter polymorphism and an exon-1 mutation (G71R) in the UGT1A1 gene in neonates with unexplained hyperbilirubinemia and direct Coombs-negative [DC(-)] ABO incompatibility.

METHODS

Two-hundred term neonates in their first week of life and without additional icterogenic factors were included in the study. Neonates with a serum total bilirubin (STB) level ≥17 mg/dL constituted the hyperbilirubinemia group (n = 100), while the control group comprised healthy neonates with a STB level <12.9 mg/dL (n = 100). The cases were further subdivided into unexplained hyperbilirubinemia (n = 50), ABO(+) hyperbilirubinemia (n = 50), ABO(-) control (n = 50), and ABO(+) control (n = 50) groups on the basis of the presence or absence of DC(-) ABO incompatibility. DNA was isolated from peripheral blood and amplified by PCR, and UGT1A1 gene promoter and exon-1 were sequenced to verify sequence alterations.

RESULTS

The frequency of TA6/6, TA6/7, TA7/7, and GGA/GGA, GGA/AGA, AGA/AGA genotypes was found to be 63.5%, 21%, 15.5%, and 91.5%, 8%, 0.5%, respectively. While both heterozygous and homozygous TA7 polymorphism increased risk of hyperbilirubinemia in the ABO(+) hyperbilirubinemia group (heterozygous OR 16.76, 95% CI:3.52-79.70, p < 0.0001; homozygous OR 6.81, 95% CI:1.98-23:42, p = 0.002), only heterozygous TA7 polymorphism increased jaundice risk (OR 5.08 95% CI:76-14.65, p = 0.003) in unexplained hyperbilirubinemia. But, the coexistence of G71R mutation and promoter polymorphism or G71R mutation and DC(-) ABO incompatibility did not increase the severity of hyperbilirubinemia (p > 0.05).

CONCLUSIONS

UGT1A1 gene promoter polymorphism and G71R mutation are possible risk factors for Turkish neonates with DC(-) ABO incompatibility and unexplained 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.

UGT1A1 gene mutations and neonatal hyperbilirubinemia in Guangxi Heiyi Zhuang and Han populations

BACKGROUND

Uridine diphosphoglucuronate-glucuronosyltransferase 1A1 (UGT1A1) gene mutation was shown to be responsible for neonatal hyperbilirubinemia. This study aimed to investigate whether UGT1A1 gene mutation is associated with neonatal hyperbilirubinemia in Guangxi Heiyi Zhuang and Han populations.

METHODS

Two hundred and eighteen infants with hyperbilirubinemia (118 Heiyi Zhuang, 100 Han) and 190 control subjects (110 Heiyi Zhuang, 80 Han) were enrolled. Polymerase chain reaction and gene sequencing were used to detect the TATA-box and exon 1 of UGT1A1.

RESULTS

(TA)7 insertion mutation, 211G>A (G71R), 686C>A (P229Q), and 189C>T (D63D) were detected. Logistic regression analysis showed odds ratios (OR) of 2.64 (95% confidence interval (CI) 1.64-4.24; P < 0.001) and 0.69 (95%CI 0.43-1.10; P = 0.115) for neonates who carried UGT1A1 G71R and (TA)7 insertion mutation, respectively. G71R homozygosity increased the odds of dangerous bilirubin levels by a factor 34.23, and G71R heterozygosity only by 2.10.

CONCLUSION

We found that UGT1A1 G71R mutation is a risk factor for neonatal hyperbilirubinemia in Guangxi Heiyi Zhuang and Han populations. Meanwhile, the UGT1A1 (TA)7 insertion mutation is not associated with neonatal hyperbilirubinemia in the two ethnic groups.

Extreme neonatal hyperbilirubinemia and a specific genotype: a population-based case-control study

OBJECTIVES

Extreme hyperbilirubinemia (plasma bilirubin ≥ 24.5 mg/dL) is an important risk factor for severe bilirubin encephalopathy. Several risk factors for hyperbilirubinemia are known, but in a large number of patients, a causal factor is never established. UGT1A1 is the rate-limiting enzyme in bilirubin's metabolism. The genotype of Gilbert syndrome, the UGT1A1*28 allele, causes markedly reduced activity of this enzyme, but its association with neonatal hyperbilirubinemia is uncertain and its relationship with extreme hyperbilirubinemia has not been studied. We examined whether the UGT1A1*28 allele is associated with extreme hyperbilirubinemia.

METHODS

The UGT1A1*28 allele was assessed in a case-control study of 231 white infants who had extreme hyperbilirubinemia in Denmark from 2000 to 2007 and 432 white controls. Cases were identified in the Danish Extreme Hyperbilirubinemia Database that covers the entire population. Genotypes were obtained through the Danish Neonatal Screening Biobank. Subgroup analysis was done for AB0 incompatible cases.

RESULTS

No association was found between the UGT1A1*28 allele and extreme hyperbilirubinemia. With the common genotype as reference, the odds ratio of extreme hyperbilirubinemia was 0.87 (range, 0.68-1.13) for UGT1A1*28 heterozygotes and 0.77 (range, 0.46-1.27) for homozygotes. Also, no association was found for AB0 incompatible cases.

CONCLUSIONS

The UGT1A1*28 allele was not associated with risk for extreme hyperbilirubinemia in this study.

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.

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.

Risk factors for severe hyperbilirubinemia among infants with borderline bilirubin levels: a nested case-control study

OBJECTIVE

To estimate the effect of phototherapy and other predictors on the risk of total serum bilirubin (TSB) >or= 25 mg/dL in infants with a TSB of 17 to 22.9 mg/dL at age >or= 48 hours.

STUDY DESIGN

From a cohort of 285295 infants >or= 34 weeks gestation and >or= 2000 g born between 1995 and 2004 in northern California Kaiser hospitals, we identified 17986 with a TSB of 17 to 22.9 mg/dL at age >or= 48 hours. All infants exhibiting a TSB >or= 25 mg/dL were selected as cases for the study. Four randomly selected controls were matched to each case based on the difference between their qualifying TSB and the American Academy of Pediatrics' phototherapy threshold.

RESULTS

A total of 62 cases were identified (0.4%). Six of these (10%) received inpatient phototherapy within 8 hours, along with 101 controls (41%) (adjusted odds ratio [AOR] 0.15; 95% confidence interval [CI] 0.06 to 0.40). Cases more often had lower gestational age (AOR 3.24; 95% CI 1.24 to 8.47 for 38 to 39 weeks and AOR = 3.70; 95% CI 0.61 to 22.4 for 34 to 37 weeks compared with >or= 40-week infants), bruising, (AOR 2.52; 95% CI 1.16 to 5.50), exclusive breast-feeding (AOR 2.09; 95% CI 1.05 to 4.03), and TSB increase of >or= 6 mg/dL/day (AOR 2.39; 95% CI 1.18 to 4.85).

CONCLUSIONS

Phototherapy was 85% effective in preventing TSB >or= 25 mg/dL. The strongest predictors of TSB >or= 25 mg/dL were gestational age, bruising, family history, and rapid rise in TSB.

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.

(TA)n UDP-glucuronosyltransferase 1A1 promoter polymorphism in Nigerian neonates

Nigerian neonates have a high incidence of bilirubin encephalopathy. Glucose-6-phosphate dehydrogenase (G-6-PD) deficiency is prevalent in this population. (TA)7 promoter polymorphism in the gene encoding the bilirubin conjugating enzyme UDP-glucuronosyltransferase 1A1 (UGT1A1) potentiates hyperbilirubinemia in G-6-PD deficient neonates. We studied (TA)n allele frequency to determine, at least in part, its contribution to the frequency and severity of hyperbilirubinemia. DNA was extracted from umbilical cord blood of sequentially born Nigerian neonates and the (TA)n UGT1A1 promoter sequence determined. The (TA)n allele distribution was compared with reported adults of varying African ancestry and Sephardic Jewish neonates. Among 88 Nigerian neonates, (TA)6 and (TA)7 alleles were almost equally distributed (0.46 and 0.43, respectively). Some individuals with (TA)5 and (TA)8 sequences were encountered. Allele distribution was similar to that of the African ancestry population but differed from the Sephardic Jewish newborns, in whom the (TA)6/(TA)7 distribution was 0.65/0.35. Whereas 45% of Nigerian alleles and 50% of African ancestry alleles, respectively, included a (TA)7 or (TA)8 sequence, only 35% of Jewish alleles were (TA)7 (p < 0.001), and no (TA)8 alleles were encountered. The high frequency of (TA)n promoter polymorphism, coupled with G-6-PD deficiency, may contribute to the pathogenesis of extreme neonatal hyperbilirubinemia in Nigeria.

Cord blood bilirubin level in relation to bilirubin UDP-glucuronosyltransferase gene missense allele in Chinese neonates

AIM

To investigate bilirubin UDP-glucuronosyltransferase (UGT1A1) gene allele in healthy Chinese neonates, their cord bilirubin level and the subsequent hyperbilirubinemia to determine relationships among them.

METHODS

Cord blood of 48 neonates was obtained to determine the exon 1 of UGT1A1 gene, total serum bilirubin, albumin, glutamic-pyruvic transaminase (GPT), glutamic-oxalacetic transaminase (GOT) and haemoglobin (Hb) concentration. Neonatal jaundice was assessed by measurement of transcutaneous bilirubin (TCB) and serum bilirubin. Neonates were divided into two groups according to mutant or normal allele to compare the variables.

RESULTS

Nineteen infants had the nucleotide 211 G-->A allele, 3 had the heterozygous variation (686C-->A, 845 A-->T, 231G-->A). In the 211 A allele group, cord bilirubin was significantly higher than in the 211 G allele group (p = 0.034), but there were no differences in albumin (p = 0.678), GPT (p = 0.460), GOT (p = 0.440) and Hb (p = 0.886). The TCB (at 48, 96 h), the frequency of the hyperbilirubinemia and prolonged jaundice were also significantly higher in the 211 A allele group.

CONCLUSIONS

The UGT1A1 gene codon G71R allele is a risk factor for neonatal hyperbilirubinemia in the Chinese population. Its effect on bilirubin metabolism may present early on, as well as late in foetal life.

Molecular mechanism of phase I and phase II drug-metabolizing enzymes: implications for detoxification

Enzymes that catalyze the biotransformation of drugs and xenobiotics are generally referred to as drug-metabolizing enzymes (DMEs). DMEs can be classified into two main groups: oxidative or conjugative. The NADPH-cytochrome P450 reductase (P450R)/cytochrome P450 (P450) electron transfer systems are oxidative enzymes that mediate phase I reactions, whereas the UDP-glucuronosyltransferases (UGTs) are conjugative enzymes that mediate phase II enzymes. Both enzyme systems are localized to the endoplasmic reticulum (ER) where a number of drugs are sequentially metabolized. DMEs, including P450s and UGTs, generally have a highly plastic active site that can accommodate a wide variety of substrates. The P450 and UGT genes constitute a supergene family, in which UGT proteins are encoded by distinct genes and a complex gene. Both the P450 and UGT genes have evolved to diversify their functions. This chapter reviews advances in understanding the structure and function of the P450R/P450 and UGT enzyme systems. In particular, the coordinate biotransformation of xenobiotics by phase I and II enzymes in the ER membrane is examined.

Biochemistry testing associated with pregnancy and the newborn period -- a lot has changed since you were a baby!

Everyone has been a newborn, and everyone's mother has been pregnant. Despite the commonality of these events, medical care and the clinical chemistry laboratory's role in it have changed remarkably over the last 50 years. This review is a historical overview of clinical chemistry testing that is related to pregnancy and the newborn period.

The effectiveness of oral tin mesoporphyrin prophylaxis in reducing bilirubin production after an oral heme load in a transgenic mouse model

BACKGROUND

Neonatal jaundice is commonly encountered and rarely associated with morbidity and mortality. Nonetheless, infants with glucose-6-phosphate dehydrogenase deficiency often have hemolysis (a heme load) caused by an environmental oxidant trigger, thus increasing their risk for serious morbidity. The use of tin mesoporphyrin (SnMP) has been proposed for interdicting the development of severe hyperbilirubinemia in a variety of conditions.

OBJECTIVES

We studied the in vivo effects of prophylactic oral SnMP on heme oxygenase (HO) activity and bilirubin production, as indexed by the excretion rate of carbon monoxide (VeCO), following a subsequent oral heme load.

METHODS

Adult mice were exposed serially to heme and assessed for in vivo bilirubin production rates, HO-1 transcription and protein, and HO activity. The effect of prophylaxis with a single oral dose of SnMP prior to an oral heme load was assessed by measuring VeCOand tissue HO activities.

RESULTS

After serial heme exposures, VeCO, HO-1 transcription and protein, and liver and spleen HO activities increased incrementally. After pretreatment with oral SnMP, bilirubin production decreased in response to an oral heme load. Also, heme-mediated increases in liver, spleen, and intestine HO activities were significantly dampened.

CONCLUSIONS

A single oral dose of SnMP results in durable inhibition of bilirubin production and HO activity for at least 24 h in a mouse model of oral heme loading. Further studies are needed to fully elucidate the duration of this protection against hyperbilirubinemia due to a delayed heme load and any long-term consequences of prophylaxis with SnMP on HO-1 transcription and HO-1 protein.

Vigintiphobia revisited

In this review the historical tenets and evidence-based clinical research in support of a bilirubin exchange threshold of >20 mg/dL for the healthy term neonate are revisited. In addition, a hypothesis is ventured that recent cases of kernicterus are related in part to changes in population factors coupled with genetic predispositions that have unmasked an unappreciated potential for marked neonatal hyperbilirubinemia.