Conjugated bilirubin in neonates with glucose-6-phosphate dehydrogenase deficiency

Pleiotropic Outcomes of Glyphosate Exposure: From Organ Damage to Effects on Inflammation, Cancer, Reproduction and Development

Glyphosate is widely used worldwide as a potent herbicide. Due to its ubiquitous use, it is detectable in air, water and foodstuffs and can accumulate in human biological fluids and tissues representing a severe human health risk. In plants, glyphosate acts as an inhibitor of the shikimate pathway, which is absent in vertebrates. Due to this, international scientific authorities have long-considered glyphosate as a compound that has no or weak toxicity in humans. However, increasing evidence has highlighted the toxicity of glyphosate and its formulations in animals and human cells and tissues. Thus, despite the extension of the authorization of the use of glyphosate in Europe until 2022, several countries have begun to take precautionary measures to reduce its diffusion. Glyphosate has been detected in urine, blood and maternal milk and has been found to induce the generation of reactive oxygen species (ROS) and several cytotoxic and genotoxic effects in vitro and in animal models directly or indirectly through its metabolite, aminomethylphosphonic acid (AMPA). This review aims to summarize the more relevant findings on the biological effects and underlying molecular mechanisms of glyphosate, with a particular focus on glyphosate's potential to induce inflammation, DNA damage and alterations in gene expression profiles as well as adverse effects on reproduction and development.

Glucose-6-phosphate dehydrogenase deficiency and susceptibility to childhood diseases in Kilifi, Kenya

Few previous studies have reported the effects of glucose-6-phosphate dehydrogenase (G6PD)-deficiency on child health in Africa. We conducted a case-control study in which cases (n = 6829) were children admitted, for any reason, to Kilifi County Hospital, Kenya, while controls (n = 10 179) were recruited from the surrounding community. Cases were subclassified based on their clinical and laboratory findings at admission. We calculated the prevalence of specific diseases by G6PD c.202 genotype, the only significant cause of G6PD-deficiency in this area, then estimated the association between genotype and admission with specific conditions using logistic regression.  Among neonates, the prevalence of jaundice was higher in both G6PD c.202T heterozygotes (40/88; 45.5%; P = .004) and homo/hemizygotes (81/134; 60.5%; P < .0001) than in wild-type homozygotes (157/526; 29.9%). Median bilirubin levels also increased across the groups, being highest (239 mmol/L; interquartile range 96-390 mmol/L) in G6PD c.202T homo/hemizygotes. No differences were seen in admission hemoglobin concentrations or the prevalence of anemia or severe anemia by G6PD c.202 genotype. On case control analysis, G6PD heterozygosity was negatively associated with all-cause hospital admission (odds ratio 0.81; 95% confidence interval 0.73-0.90; P < .0001) and, specifically, admission with either pneumonia or Plasmodium falciparum parasitemia; while, conversely, it was positively associated with Gram-positive bacteremia. G6PD c.202T homo/heterozygosity was positively associated with neonatal jaundice, severe pneumonia, the receipt of a transfusion, and in-patient death. Our study supports the conclusion that G6PD c.202T is a balanced polymorphism in which a selective advantage afforded to heterozygous females against malaria is counterbalanced by increased risks of neonatal jaundice, invasive bacterial infections, and anemia.

The Preterm Infant: A High-Risk Situation for Neonatal Hyperbilirubinemia Due to Glucose-6-Phosphate Dehydrogenase Deficiency

Prematurity and glucose-6-phosphate dehydrogenase (G6PD) deficiency are risk factors for neonatal hyperbilirubinemia. The 2 conditions may interact additively or synergistically, contributing to extreme hyperbilirubinemia, with the potential for bilirubin neurotoxicity. This hyperbilirubinemia is the result of sudden, unpredictable, and acute episodes of hemolysis in combination with immaturity of bilirubin elimination, primarily of conjugation. Avoidance of contact with known triggers of hemolysis in G6PD-deficient individuals will prevent some, but not all, episodes of hemolysis. All preterm infants with G6PD deficiency should be vigilantly observed for the development of jaundice both in hospital and after discharge home.

Glyphosate, pathways to modern diseases III: Manganese, neurological diseases, and associated pathologies

Manganese (Mn) is an often overlooked but important nutrient, required in small amounts for multiple essential functions in the body. A recent study on cows fed genetically modified Roundup(®)-Ready feed revealed a severe depletion of serum Mn. Glyphosate, the active ingredient in Roundup(®), has also been shown to severely deplete Mn levels in plants. Here, we investigate the impact of Mn on physiology, and its association with gut dysbiosis as well as neuropathologies such as autism, Alzheimer's disease (AD), depression, anxiety syndrome, Parkinson's disease (PD), and prion diseases. Glutamate overexpression in the brain in association with autism, AD, and other neurological diseases can be explained by Mn deficiency. Mn superoxide dismutase protects mitochondria from oxidative damage, and mitochondrial dysfunction is a key feature of autism and Alzheimer's. Chondroitin sulfate synthesis depends on Mn, and its deficiency leads to osteoporosis and osteomalacia. Lactobacillus, depleted in autism, depend critically on Mn for antioxidant protection. Lactobacillus probiotics can treat anxiety, which is a comorbidity of autism and chronic fatigue syndrome. Reduced gut Lactobacillus leads to overgrowth of the pathogen, Salmonella, which is resistant to glyphosate toxicity, and Mn plays a role here as well. Sperm motility depends on Mn, and this may partially explain increased rates of infertility and birth defects. We further reason that, under conditions of adequate Mn in the diet, glyphosate, through its disruption of bile acid homeostasis, ironically promotes toxic accumulation of Mn in the brainstem, leading to conditions such as PD and prion diseases.

Association between G6PD deficiency and hyperbilirubinemia in neonates: a meta-analysis

Hyperbilirubinemia is prevalent in newborns and multiple factors are responsible for the occurrence of neonatal hyperbilirubinemia. G6PD (Glucose-6-Phosphate Dehydrogenase) deficiency is recognized as one of the risk factors. However, many pediatricians did not take into account the probable effect of G6PD-deficiency when severe neonatal hyperbilirubinemia occurred. The aim of the present study was to perform a meta-analysis to investigate whether G6PD-deficiency increases the risk of hyperbilirubinemia and phototherapy in newborn. We searched PubMed and Embase databases for eligible articles according to explicit study inclusion and exclusion criteria. Risk ratios (RRs) and 95% confidence interval (CI) were selected as the evaluation indexes. Cochrane Q and I(2) test were utilized to assess the heterogeneity among studies. A total of five cohort studies were included in this meta-analysis. There were 21,585 participants enrolled in these studies including 877 newborns with hyperbilirubinemia and 261 newborns receiving phototherapy. Comparison of the incidence of hyperbilirubinemia in newborns with G6PD-deficiency to the ones with normal G6PD in each study yielded a pooled RR of 3.92 (95% CI, 2.13-7.20; P <.0001). The pooled RR of receiving phototherapy in G6PD-deficiency neonates is 3.01 (95% CI, 2.20-4.12; P <.0001) when compared to G6PD normal neonates. This study revealed a significant correlation between G6PD-deficiency and neonatal hyperbilirubinemia, as well as G6PD-deficiency and phototherapy. G6PD-deficient newborns have higher risk of hyperbilirubinemia and phototherapy than the ones with normal G6PD. Monitoring the level of G6PD in newborns is important for predicting the occurrence of hyperbilirubinemia.

Neonatal hemolysis and risk of bilirubin-induced neurologic dysfunction

The pathologic phenotype of severe hyperbilirubinemia in the newborn infant is primarily due to excessive bilirubin production and/or impaired conjugation, resulting in an increased bilirubin load. This may, in turn, increase an infant's risk for the development of bilirubin-induced neurologic dysfunction (BIND). The highest-risk infants are those with increased bilirubin production rates due to hemolysis. Several immune and non-immune conditions have been found to cause severe hemolysis, and these are often exacerbated in those infants with perinatal sepsis and genetic predispositions. Therefore, identification of these infants, with novel technologies, is paramount in reducing the incidence of BIND and the long-term neurologic sequelae for these at-risk infants.

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.

Heme oxygenase-1 promoter polymorphisms and neonatal jaundice

BACKGROUND

Heme oxygenase (HO) is the initial, rate-limiting enzyme in the conversion of heme to bilirubin. Dinucleotide (GT)n repeat length in the promoter region of the encoding gene modulates transcription: shorter alleles, in contrast with longer allele counterparts, are associated with greater gene expression and should result in increased heme catabolism.

OBJECTIVE

We compared the rates of heme catabolism and plasma total bilirubin (TB) between HO-1 promoter genotypes of varying (GT)n repeat lengths in glucose-6-phosphate dehydrogenase (G6PD)-normal and -deficient neonates.

METHODS

HO-1 promoter length was determined from genomic DNA from previous studies by size discrimination of fluorescently-labeled PCR products with capillary electrophoresis. Sizing was confirmed by sequencing homozygote samples. Alleles were categorized as: short (≤24 GT repeats), medium (25-33 GT repeats), and long (≥34 GT repeats). Previously determined values for blood carboxyhemoglobin, corrected for inspired carbon monoxide (COHbc), and TB were used to determine the rate of heme catabolism and 3rd day TB values for each HO-1 promoter length genotype, respectively. G6PD Mediterranean was determined by PCR analysis.

RESULTS

Neither COHbc nor TB values were significantly different between various HO-1 promoter genotypes for either G6PD-normal or -deficient neonates.

CONCLUSIONS

In the steady state, HO-1 promoter genotypes, based on the length of (GT)n repeats, do not modulate heme catabolism or 3rd day TB values in either G6PD-normal or -deficient neonates.

Glucose-6-phosphate dehydrogenase deficiency in neonatal hyperbilirubinaemia: Hacettepe experıence

AIM

The aim of this study was to investigate the prevalence of glucose-6-phospate dehydrogenase (G6PD) deficiency in newborn infants with neonatal hyperbilirubinaemia and to compare the clinical features of G6PD-deficient and G6PD-normal newborn infants.

METHODS

A total of 4906 term and preterm neonates with indirect hyperbilirubinaemia were retrospectively evaluated according to demographic, neonatal features, bilirubin levels, erythrocyte G6PD levels, other risk factors and treatments.

RESULTS

Among 4906 newborn infants with indirect hyperbilirubinaemia, 55 (1.12%) neonates were G6PD-deficient. In our study, no statistically significant difference was detected between G6PD-deficient and G6PD-normal infants in relation to the time of onset of jaundice, bilirubin levels and duration of phototherapy. However, the incidence of exchange transfusion in G6PD-deficient infants was 16.4% while it was only 3.3% in G6PD normal infants (P < 0.05).

CONCLUSION

Testing for G6PD must be ordered to all newborns who are receiving phototherapy and especially to those who are coming from the high incident geographical regions and less responsive to phototherapy.

Severe neonatal hyperbilirubinemia and kernicterus: are these still problems in the third millennium?

Despite efforts to eliminate permanent and irreversible brain damage due to bilirubin encephalopathy and kernicterus, these conditions continue to accompany us into the third millennium. This phenomenon occurs not only in developing countries with emerging medical systems, but in Westernized countries as well. Comprehensive guidelines to detect newborns with jaundice and treat those in whom hyperbilirubinemia has already developed have been formulated in several countries, but have not been successful in completely eliminating the problem. In this appraisal of the situation we review selected aspects of bilirubin encephalopathy and/or kernicterus. We highlight recent reports of severe hyperbilirubinemia and kernicterus, discuss some of the factors responsible for the continuing appearance of these conditions, and briefly review what can be done to decrease bilirubin-related morbidity and mortality to the minimum.

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.

The need for neonatal glucose-6-phosphate dehydrogenase screening: a global perspective

Glucose-6-phosphate dehydrogenase (G-6-PD) deficiency is an important cause of severe neonatal hyperbilirubinemia, and is overrepresented, even in countries with a low overall incidence of the enzyme deficiency, in the etiology of kernicterus. Neonatal screening for G-6-PD deficiency before discharge from the birth hospitalization should be instrumental in increasing parental and medical caretaker awareness of the high-risk nature of an infant, thereby effecting earlier referral of hyperbilirubinemic neonates for medical evaluation and treatment. The need for global screening, timing of screening, and the pros and cons of biochemical versus molecular DNA screening were discussed at the Newborn Jaundice and Kernicterus Meeting in Siena. The participants agreed that there was a need to expand neonatal G-6-PD screening globally and that screening results should be obtained before the infants' discharge from birth hospitalization.

Severe hemolysis with normal blood count in a glucose-6-phosphate dehydrogenase deficient neonate

A premature glucose-6-phosphate dehydrogenase (G-6-PD) deficient neonate was readmitted for exponential rise in the plasma bilirubin concentration to 33.0 mg dl(-1). Blood carboxyhemoglobin (2.8% of total hemoglobin, >threefold normal value) confirmed the presence of hemolysis; however, hematological indices were unchanged from the birth hospitalization. Serum unbound bilirubin, although present, was probably at a concentration insufficient to cause bilirubin encephalopathy. In G-6-PD deficient neonates, severe hemolysis may occur in the absence of hematological changes typical of a hemolytic process.

Glucose-6-phosphate dehydrogenase deficiency

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common human enzyme defect, being present in more than 400 million people worldwide. The global distribution of this disorder is remarkably similar to that of malaria, lending support to the so-called malaria protection hypothesis. G6PD deficiency is an X-linked, hereditary genetic defect due to mutations in the G6PD gene, which cause functional variants with many biochemical and clinical phenotypes. About 140 mutations have been described: most are single base changes, leading to aminoacid substitutions. The most frequent clinical manifestations of G6PD deficiency are neonatal jaundice, and acute haemolytic anaemia, which is usually triggered by an exogenous agent. Some G6PD variants cause chronic haemolysis, leading to congenital non-spherocytic haemolytic anaemia. The most effective management of G6PD deficiency is to prevent haemolysis by avoiding oxidative stress. Screening programmes for the disorder are undertaken, depending on the prevalence of G6PD deficiency in a particular community.

(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.

(TA)n UGT 1A1 promoter polymorphism: a crucial factor in the pathophysiology of jaundice in G-6-PD deficient neonates

Increased heme catabolism has been reported in glucose-6-phosphate dehydrogenase (G-6-PD)-normal neonates who were also homozygous for (TA)7/(TA)7 (UGT1A1*28) uridine diphosphoglucuronate-glucuronosyltransferase 1A1 (UGT) promoter polymorphism (Gilbert syndrome). As G-6-PD deficiency is associated with increased hemolysis, we hypothesized that in G-6-PD-deficient neonates who also have the (TA)7/(TA)7 UGT promoter genotype, steady-state hemolysis would be even further increased. Male G-6-PD-deficient neonates were sampled for plasma total bilirubin (PTB), blood carboxyhemoglobin corrected for inhaled carbon monoxide in ambient air (COHbc) (an index of heme catabolism), and UGT (TA)n promoter genotype determination and compared with previously published G-6-PD-normal neonates. Although COHbc values were higher in the G-6-PD-deficient than in the G-6-PD-normal cohorts (0.97 +/- 0.32% of total Hb (tHb) versus 0.76 +/- 0.19% of tHb, p < 0.001), PTB values were similar (9.2 +/- 3.4 mg/dL versus 8.9 +/- 3.0 mg/dL, respectively, p = 0.3). Within the G-6-PD-deficient group, although COHbc values were alike between the three UGT promoter genotypes, PTB was higher in the (TA)7/(TA)7 homozygotes (11.1 +/- 4.0 mg/dL) compared with (TA)6/(TA)7 heterozygotes (9.1 +/- 3.2 mg/dL, p = 0.03) and wild-type (TA)6/(TA)6 homozygotes (8.8 +/- 3.4 mg/dL, p = 0.02). In the steady state, similar rates of hemolysis, but increased PTB in the G-6-PD- deficient, (TA)7/(TA)7 homozygotes, imply that (TA)7/(TA)7, homozygosity is central to increased PTB.

Studies in hemolysis in glucose-6-phosphate dehydrogenase-deficient African American neonates

BACKGROUND

The role of hemolysis in the mechanism and prediction of hyperbilirubinemia was contrasted between glucose-6-phosphate dehydrogenase (G-6-PD)-deficient and -normal African American neonates.

METHODS

Corrected end tidal carbon monoxide (ETCOc) values from the subset of male neonates born to non-smoking African American mothers, drawn from a previously published study, were analyzed. The relationship between ETCOc and bilirubin values, the latter represented as percentiles on the hour of life specific bilirubin nomogram, was determined. Hyperbilirubinemia was defined as any bilirubin value > or =95th percentile for hour of life.

RESULTS

18.6% of 59 G-6-PD-deficient neonates developed hyperbilirubinemia, compared with 7.5% of 362 controls (relative risk 2.50, 95% confidence interval 1.31 to 4.76). As reported, ETCOc values (median, interquartile range) were significantly higher among G-6-PD-deficient neonates than controls (2.4 [2.0-2.9] vs. 2.1 [1.7-2.5] ppm, p<0.001. However, higher ETCOc values were limited to those G-6-PD-deficient neonates with lower bilirubin percentiles: among those whose bilirubin value did not exceed the 95th percentile ETCOc was 2.30 [2.00-2.85] vs. 2.00 [1.70-2.40] ppm in controls, p=0.001. In contrast, among the hyperbilirubinemic neonates ETCOc values were similar between G-6-PD-deficient neonates and controls: 2.7 [2.03-3.33] vs. 2.6 [2.33-3.45] ppm, p=0.9. In the G-6-PD-deficient neonates ETCOc > or =75th percentile contributed no additional predictive value for hyperbilirubinemia (likelihood ratio 1.8).

CONCLUSIONS

G-6-PD-deficient African American neonates have increased hemolysis and increased rate of hyperbilirubinemia, but the hemolysis is neither a predominant factor in the pathogenesis of hyperbilirubinemia nor is it predictive of hyperbilirubinemia, over and above the already increased risk conferred by G-6-PD deficiency.

Glucose-6-phosphate dehydrogenase deficiency in triplets of African-American descent

Despite the prevalence of glucose-6-phosphate dehydrogenase (G6PD) deficiency in African Americans, the disorder maybe often overlooked as a diagnosis in the absence of overt signs of hemolysis in neonates with hyperbilirubinemia. We present a case report of anemia and prolonged hyperbilirubinemia due to G6PD deficiency in the absence of hemolysis in dichorionic, triamniotic, preterm triplets of African-American descent.

Poor correlation between hemolysis and jaundice in glucose 6-phosphate dehydrogenase-deficient babies

BACKGROUND

The role of hemolysis in the pathophysiology of neonatal jaundice (NNJ) in patients with glucose 6-phosphate dehydrogenase (G6PD) deficiency has been questioned recently. The aim of the present study was to determine the contribution of hemolysis to the pathophysiology of jaundice in Malay neonates with G6PD deficiency and NNJ.

METHODS

Four groups of babies were included in the study: (i) G6PD deficient with NNJ; (ii) G6PD deficient without NNJ; (iii) G6PD normal with NNJ; and (iv) normal controls. Babies with other known causes of jaundice were excluded from the study. All subjects underwent the following investigations on day 3-5 after birth: hemoglobin level (Hb), serum bilirubin level, carboxyhemoglobin (CO-Hb) concentration, reticulocyte count and full blood picture. The results of the investigations were compared between the groups using SPSS version 11.

RESULTS

Babies with G6PD and jaundice had a similar percentage of CO-Hb to babies with G6PD without NNJ or babies with normal G6PD and NNJ (1.76 +/- 0.40% vs 1.66 +/- 0.31% and 1.67 +/- 0.28%, respectively; P: 0.23 and 0.41, respectively). Total Hb levels and reticulocyte counts were not significantly different between the groups. The blood film showed more (even though not reaching significance) hemolysis in the G6PD patients but results of the blood film were very similar for G6PD patients with and those without NNJ.

CONCLUSION

Hemolysis is not a main determinant of neonatal jaundice in G6PD-deficient babies.

Neonatal bilirubin production-conjugation imbalance: effect of glucose-6-phosphate dehydrogenase deficiency and borderline prematurity

OBJECTIVE

To evaluate relations between production and conjugation of bilirubin in the pathophysiology of jaundice in glucose-6-phosophate dehydrogenase (G6PD) deficient neonates.

METHODS

Term and borderline premature (35-37 weeks gestational age), healthy, male, G6PD deficient neonates were studied close to the beginning of the 3rd day. Blood carboxyhaemogobin corrected for inspired CO (COHbc; an index of bilirubin production) and serum total conjugated bilirubin (TCB; a reflection of bilirubin conjugation) were measured in simultaneously drawn blood samples by gas chromatography and reverse phase high performance liquid chromatography respectively. A bilirubin production-conjugation index comprising COHbc/TCB was determined; a high index reflects imbalance between the bilirubin production and conjugation processes. COHbc and TCB individually and the production-conjugation index were studied in relation to serum total bilirubin (STB) concentration.

RESULTS

Fifty one G6PD deficient neonates were sampled at 51 (8) hours. COHbc values did not correlate with STB (r=0.22, p=0.15). TCB did correlate inversely with STB (r=-0.42, p=0.004), and there was a positive correlation between the production-conjugation index and STB (r=0.45, p=0.002). The production-conjugation index (median (interquartile range)) was higher in the premature (n=8) than term neonates (2.31 (2.12-3.08) v 1.05 (0.53-1.81), p=0.003). This difference was the result of changes in TCB.

CONCLUSIONS

The data show that jaundice in G6PD deficient neonates is the result of an imbalance between production and conjugation of bilirubin with a tendency for inefficient bilirubin conjugation over increased haemolysis in its pathogenesis. Borderline premature infants are at special risk of bilirubin production-conjugation imbalance.

Glucose-6-phosphate dehydrogenase deficiency: a hidden risk for kernicterus

Glucose-6-phosphate dehydrogenase (G-6-PD) deficiency, a commonly occurring enzymatic defect, is an important risk factor in the pathogenesis of severe neonatal hyperbilirubinemia. Many of the recently reported cases of kernicterus, even in countries with a low overall incidence of the G-6-PD deficiency such as the United States and Canada, have been found to be enzyme deficient. In many cases the hyperbilirubinemia may be due to acute hemolysis precipitated by exposure to an identifiable chemical trigger, or to infection. In other cases the hemolysis may be mild, the hyperbilirubinemia being due to diminished bilirubin conjugation. An interaction between G-6-PD deficiency and promoter polymorphism for the gene encoding the bilirubin conjugating enzyme, UDP-glucuronosyltranferase 1A1, associated with Gilbert syndrome, has been implicated in the pathogenesis of hyperbilirubinemia. Neonates whose families originated in areas at high risk for G-6-PD deficiency should be vigilantly observed for jaundice. Phototherapy is the mainstay of treatment, with exchange transfusion being performed in those unresponsive to phototherapy. A high degree of physician awareness is essential in the identification and follow-up of these high-risk neonates.

Hyperbilirubinemia among African American, glucose-6-phosphate dehydrogenase-deficient neonates

BACKGROUND

Although glucose-6-phosphate dehydrogenase (G-6-PD) deficiency is prevalent in African Americans, their risk of associated neonatal hyperbilirubinemia has not been prospectively studied.

OBJECTIVE

To compare hemolysis and the risk of hyperbilirubinemia among African American, G-6-PD-deficient neonates (study group) and G-6-PD-normal control subjects.

METHODS

Consecutive, healthy, term and near-term, male neonates born to African American mothers comprised the patient cohort. G-6-PD testing was performed with umbilical cord blood samples. Routine management included measurement of the end tidal carbon monoxide level corrected for ambient carbon monoxide level (ETCOc) within 4 hours after delivery (assessment of hemolysis), > or =1 predischarge bilirubin determination, and additional bilirubin testing as clinically indicated. Indications for phototherapy were identical for study patients and control subjects. Neonates were monitored for the first 1 week of life. ETCOc results, the incidence of hyperbilirubinemia (defined as a transcutaneous or plasma total bilirubin concentration of > or =95th percentile for the hour of life), and the need for phototherapy were compared between the G-6-PD-deficient and G-6-PD-normal groups.

RESULTS

Five hundred male patients were enrolled, of whom 64 (12.8%) were G-6-PD-deficient. ETCOc values (median and interquartile range) were higher among G-6-PD-deficient neonates than among control neonates (2.4 ppm [2.0-2.9 ppm] vs 2.1 ppm [1.7-2.5 ppm]). More G-6-PD-deficient neonates developed hyperbilirubinemia than did control subjects (14 of 64, 21.9%, vs 29 of 436, 6.7%; relative risk: 3.27; 95% confidence interval: 1.83-5.86), whereas 13 (20.3%) met the criteria for phototherapy, compared with 25 control subjects (5.7%) (relative risk: 3.53; 95% confidence interval: 1.91-6.56). No cases of kernicterus were observed.

CONCLUSIONS

Within the African American neonatal population, there is a subgroup of G-6-PD-deficient infants with elevated rates of hemolysis, a higher incidence of hyperbilirubinemia, and a greater requirement for phototherapy, compared with G-6-PD-normal control subjects. These newborns should be monitored vigilantly for the development of hyperbilirubinemia.

Glucose-6-phosphate dehydrogenase deficiency in neonates

OBJECTIVE

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an inherited deficiency that may be the cause of neonatal hyperbilirubinemia, as has been found in several countries and among widely different ethnic groups, especially in Mediterranean region. Our aim was to study the prevalence of G6PD deficiency in relation to neonatal jaundice.

METHODS

From March 1998 to April 2001 we studied 705 clinically icteric neonates who were admitted to Al-Zahra and Beheshti hospitals, two teaching hospitals in Isfahan, Iran. Laboratory investigations included determination of direct and indirect serum bilirubin concentrations, blood group typing, direct coomb's test, hemoglobin, blood smear, reticulocyte count and G6PD level.

RESULTS

In only 53 (7.5%) of cases G6PD deficiency was diagnosed. In all G6PD deficient neonates no evidence of other factors known to cause hyperbilirubinemia were detected. The sex distribution was 13 (24.5%) females and 40 (75.5%) males in the G6PD deficient group. The mean bilirubin level in G6PD deficient and G6PD normal groups were 22.26 +/- 8.36 and 18.14 +/- 3.85 mg/dl, respectively (p=0.001). Phototherapy was required in G6PD deficient and other icteric neonates with duration of 3.76 +/- 1.93 and 3.13 +/- 2.14 days, respectively (p=0.045). Twenty-seven of the 53 (50.9%) G6PD deficient infants required exchange transfusion. None of them developed kernicterus.

CONCLUSIONS

Since the prevalence of severe hyperbilirubinemia among our neonates was relatively high and about half of them required exchange transfusion, early detection of this enzymopathy regardless of sex and close surveillance of the affected newborns may be important in reducing the risk of severe hyperbilirubinemia and exchange transfusion.

Hemolysis and hyperbilirubinemia in an African American neonate heterozygous for glucose-6-phosphate dehydrogenase deficiency

Despite recent case reports of bilirubin encephalopathy in African American glucose-6-phosphate dehydrogenase (G6PD)-deficient neonates, there is a misconception that, in African Americans, G6PD deficiency need not be considered in the differential diagnosis of hyperbilirubinemia. We present a case of a hyperbilirubinemic African American female neonate in whom coexisting G6PD deficiency in the heterozygous state, and Gilbert's syndrome, were confirmed by DNA analysis. Hemolysis, predictive of the subsequent icterus, was documented by end-tidal carbon monoxide determinations at two time periods within the first 25 hours of life. A diagnosis of G6PD deficiency should be considered in African American neonates, females as well as males, with unexplained hemolysis or hyperbilirubinemia.

Imbalance between production and conjugation of bilirubin: a fundamental concept in the mechanism of neonatal jaundice

OBJECTIVE

The objective of this study was to evaluate the roles of production and conjugation of bilirubin, individually and in combination, in the mechanism of neonatal jaundice.

METHODS

A cohort of healthy, term male newborns was sampled on the third day of life, coincident with routine metabolic screening, for blood carboxyhemoglobin determination, a reflection of heme catabolism, and for serum unconjugated and conjugated bilirubin fractions, reflecting bilirubin conjugation. The former was determined by gas chromatography, corrected for inspired CO (COHbc), and expressed as percentage of total hemoglobin. Serum bilirubin fractions were quantified by alkaline methanolysis and reverse phase high performance liquid chromatography. The sum of all bilirubin fractions comprised serum total bilirubin (STB). Total conjugated bilirubin (TCB) was comprised of the sum of the conjugated fractions and was expressed as percentage of STB (TCB[%]). A "bilirubin production/conjugation index" (COHbc/[TCB(%)] represented the combined roles of these modalities in the mechanism of bilirubinemia. Relationships between STB concentrations on the one hand, and COHbc values, TCB(%) proportions, and the production/conjugation index on the other, were determined by applying a best-fit regression analysis methodology.

RESULTS

Mean (+/- standard deviation) STB concentration at the time of sampling was 114 +/- 48 micro mol/L (range: 8-263 micro mol/L). Mean COHbc value was 0.77 +/- 0.19%, and median (interquartile range) TCB(%) was 0.737 (0.465-1.260)%. COHbc values correlated directly with STB concentrations (r = 0.38; s = 46.1), and TCB(%) correlated inversely with STB (r = 0.40; s = 45.8). The production/conjugation index correlated positively with STB values (r = 0.61; s = 45.8), the r value for the index being higher than that of either COHbc or TCB(%), individually. The bilirubin production/conjugation index seemed to have a biphasic relationship to STB: STB values rose steeply in concert with increasing index values in the lower range of the index, and subsequently plateaued in the higher range of the index.

CONCLUSIONS

Within the range of STB concentrations encountered, both increasing bilirubin production and diminishing bilirubin conjugation contributed to STB. The production/conjugation index confirmed that imbalance between production and conjugation of bilirubin plays an important role in the mechanism of neonatal bilirubinemia. alkaline methanolysis, bilirubin, bilirubin conjugation, carbon monoxide, carboxyhemoglobin, gas chromatography, hemolysis, high performance liquid chromatography, physiologic jaundice.

Glucose-6-phosphate dehydrogenase deficiency: a potential source of severe neonatal hyperbilirubinaemia and kernicterus

Glucose-6-phosphate dehydrogenase (G-6-PD) deficiency is a commonly occurring enzyme defect that can lead to severe neonatal hyperbilirubinaemia and kernicterus. Both increased haemolysis, sometimes due to an identifiable chemical trigger or to infection, and diminished bilirubin conjugation, the result of an interaction between G-6-PD deficiency and Gilbert's syndrome, contribute to the pathogenesis of the jaundice. Phototherapy is the mainstay of treatment, with exchange transfusion held in reserve for those neonates who do not respond to phototherapy. Pharmacological agents such as Sn-mesoporphyrins, which prevent bilirubin production by inhibiting the enzyme heme oxygenase, can limit hyperbilirubinaemia and possibly prevent the need for exchange transfusion. Predischarge serum total bilirubin screening is useful in predicting which neonates are at high risk for developing hyperbilirubinaemia. Migration patterns make G-6-PD deficiency a condition which may nowadays be encountered in virtually any corner of the globe and a high degree of physician awareness is essential.

Hemolysis and bilirubin conjugation in association with UDP-glucuronosyltransferase 1A1 promoter polymorphism

Hemolysis may contribute to hyperbilirubinemia in Gilbert's syndrome. The authors examined blood carboxyhemoglobin corrected for inspired CO (COHbc) to index heme catabolism and serum conjugated bilirubin fractions to reflect bilirubin conjugation. Both parameters were related to UDP-glucuronosyltransferase 1A1 (UGT) promoter polymorphism, associated with Gilbert's syndrome, in term male newborns. COHbc was expressed as percentage of total hemoglobin, and total conjugated bilirubin (TCB) value as a percentage of serum total bilirubin (STB), (TCB/STB[%]). A production/conjugation index, COHbc/(TCB/STB[%]), represented bilirubin production divided by conjugation. UGT promoter genotype was designated according to the number of promoter TA insertions in each allele: 6/6, homozygous normal; 6/7, heterozygous; 7/7, homozygous variant. STB and COHbc values were higher in the 7/7 subgroup than the other counterparts (P <.01). The COHbc/(TCB/STB[%]) was higher in the 7/7 than either the 6/6 or 6/7 subsets (1.93 [1.31-2.88] vs. 0.85 [0.51-1.72] and 0.84 [0.53-1.87], respectively; P <.01). In conclusion, 7/7 UGT promoter polymorphism was associated with increased blood COHbc values (unexpected finding) as well as diminished serum total conjugated bilirubin ratios (expected finding). The increased hemolysis may contribute to the pathogenesis of increased STB values seen in Gilbert's syndrome, and exacerbate neonatal hyperbilirubinemia associated with the promoter polymorphism.

Genetic interactions in the pathogenesis of neonatal hyperbilirubinemia: Gilbert's Syndrome and glucose-6-phosphate dehydrogenase deficiency

Glucose-6-phosphate dehydrogenase (G-6-PD) deficiency is a common condition with a worldwide distribution that has the potential for causing severe hyperbilirubinemia with bilirubin encephalopathy. Hemolysis resulting from identifiable triggers may be the cause of the jaundice in some cases, but in many, jaundice continues to occur despite avoidance of contact with known hemolytic triggers. In some G-6-PD-deficient population groups, carboxyhemoglobin studies have indicated exaggerated hemolysis; but in others, increased hemolysis has not correlated with serum total bilirubin values. As hyperbilirubinemia results from an imbalance between bilirubin production and bilirubin elimination, diminished bilirubin conjugation was suspected to contribute to the pathogenesis of hyperbilirubinemia. Serum-conjugated bilirubin fractions, reflecting intrahepatocytic bilirubin conjugation, were low in G-6-PD-deficient neonates who developed hyperbilirubinemia. This conjugated bilirubin profile was similar to that seen in adults with Gilbert's Syndrome, a condition associated with promoter polymorphism for the gene encoding the bilirubin-conjugating enzyme, UGT glucuronosyltransferase 1A1 (UGT). Whereas G-6-PD deficiency or Gilbert's Syndrome, alone, did not predispose to hyperbilirubinemia, G-6-PD-deficient neonates who also were heterozygotes or homozygotes for the variant UGT gene promoter did have significantly increased incidences of hyperbilirubinemia. Additional conditions which predispose to neonatal jaundice in the presence of Gilbert's Syndrome, include Coombs' negative ABO blood group heterospecificity, hereditary spherocytosis, and prolonged breastfeeding.Gilbert's Syndrome and G-6-PD deficiency are both common, inherited conditions. Individually, and in the absence of additional genetic or environmental factors, both are benign, and should result in minimal health disturbance or interference with the quality of life of affected individuals. However, in combination, or following exposure to environmental or other genetic factors, these benign conditions may have severe manifestations, with potentially dangerous and possibly life-threatening consequences. This review highlights the major clinical features of both Gilbert's Syndrome and G-6-PD deficiency, and surveys a series of studies related to neonatal jaundice in G-6-PD-deficient neonates culminating in the documentation of an interaction between the two conditions that is crucial to the pathogenesis of hyperbilirubinemia.

Differing pathogenesis of perinatal bilirubinemia in glucose-6-phosphate dehydrogenase-deficient versus-normal neonates

The objective was to compare the contribution to perinatal bilirubinemia of hemolysis and UDP-glucuronosyltransferase (UGT) gene promoter polymorphism, seen in Gilbert's syndrome, between glucose-6-phosphate dehydrogenase (G-6-PD)-deficient and -normal neonates. Serum total bilirubin (STB) values from 52 G-6-PD-deficient and 166 G-6-PD-normal term, male neonates, sampled within 3 h of delivery (first sample) and on d 3 (second sample), were analyzed in relation to blood carboxyhemoglobin corrected for inspired CO (COHbc), an accurate index of hemolysis, and UGT promoter genotype. COHbc values (% total Hb) were greater in G-6-PD-deficient neonates than controls: first sample 1.00 +/- 0.25% versus 0.84 +/- 0.24%, p < 0.0001; second sample 0.83 +/- 0.20% versus 0.76 +/- 0.19%, p = 0.002. First sample COHbc and STB values did not correlate in either the G-6-PD-deficient or control groups, whereas second sample COHbc values correlated significantly with corresponding STB values in the control population only (r = 0.28, p = 0.0007). At second sampling, there was a higher allele frequency of the variant UGT promoter among those with STB values > or =75th percentile than those <75th among the G-6-PD-deficient neonates (0.60 versus 0.33, respectively, p = 0.025), but not controls (0.31 versus 0.40, respectively, p = 0.24). Among those infants with at least one variant UGT promoter allele, STB values were higher in the G-6-PD-deficient neonates than controls at second sampling only (181 +/- 56 microM versus 149 +/- 46 microM, respectively, p = 0.03). Both within and between the G-6-PD-deficient and control groups, our data demonstrate changing and differing contributions of hemolysis and UGT promoter polymorphism to bilirubinemia during the first 3 d of life.

Predischarge bilirubin screening in glucose-6-phosphate dehydrogenase-deficient neonates

OBJECTIVE

To assess the validity of predischarge serum bilirubin values in determining or predicting hyperbilirubinemia in glucose-6-phosphate dehydrogenase (G-6-PD)-deficient neonates, and to facilitate appropriate discharge planning.

METHODS

Serum total bilirubin values were determined between 44 and 72 hours of life in a cohort of term, healthy neonates at high-risk for G-6-PD deficiency but with no other risk factors for hyperbilirubinemia. Percentile-based bilirubin nomograms were constructed for G-6-PD-deficient infants and normal infants according to age at sampling. The incidence of hyperbilirubinemia (serum bilirubin value > or =256 micromol/L [15 mg/dL]) for each group was determined according to the percentiles for that group.

RESULTS

In both G-6-PD-deficient neonates (n = 108) and control neonates (n = 215) with serum bilirubin values <50th percentile for age, the incidence of hyperbilirubinemia was low in the G-6-PD-deficient neonates, with no measurable incidence in the controls. The incidence of hyperbilirubinemia became clinically consequential, and significantly higher in the G-6-PD-deficient groups, when the percentiles were > or =50: for those in the 50% to 74% range the incidence was moderate (23%) for the G-6-PD-deficient and small (7%) for the control infants (relative risk, 3.29; 95% confidence interval, 1.01-10.67). Among those infants > or =75th percentile, 82% of the G-6-PD-deficient infants, compared with 25% of the control infants, were either already hyperbilirubinemic at the time of screening or subsequently developed hyperbilirubinemia (relative risk, 3.23; 95% confidence interval, 1.99-5.24).

CONCLUSIONS

Timed, predischarge serum bilirubin screening can be used to identify G-6-PD-deficient neonates at low, intermediate, or high-risk of developing severe neonatal hyperbilirubinemia, and thus offer a selective approach to the discharge and follow-up surveillance of these infants.

Glucose-6-phosphate dehydrogenase deficiency

Glucose-6-phosphate dehydrogenase (G6PD) is expressed in all tissues, where it catalyses the first step in the pentose phosphate pathway. G6PD deficiency is prevalent throughout tropical and subtropical regions of the world because of the protection it affords during malaria infection. Although most affected individuals are asymptomatic, there is a risk of neonatal jaundice and acute haemolytic anaemia, triggered by infection and the ingestion of certain drugs and broad beans (favism). A rare but more severe form of G6PD deficiency is found throughout the world and is associated with chronic non-spherocytic haemolytic anaemia. Many deficient variants of G6PD have been described. DNA sequence analysis has shown that the vast majority of these are caused by single amino acid substitutions. The three-dimensional structure of G6PD shows a classical dinucleotide binding domain and a novel beta + alpha domain involved in dimerization.

Neonatal hyperbilirubinemia in glucose-6-phosphate dehydrogenase-deficient heterozygotes

OBJECTIVES

We assessed the incidence of hyperbilirubinemia, defined as serum total bilirubin >/=15 mg/dL (256 micromol/L), in a cohort of Sephardic Jewish female neonates at risk for glucose-6-phosphate dehydrogenase (G-6-PD) deficiency with especial emphasis on the heterozygotes. We studied the roles of hemolysis by blood carboxyhemoglobin (COHb) determinations and of the variant promoter of the gene for the bilirubin-conjugating enzyme uridine 5'-diphosphate glucuronosyltransferase 1 (UGT1A1) seen in Gilbert's syndrome in the pathogenesis of the hyperbilirubinemia.

METHODS

Consecutively born, healthy, term, female neonates were screened for G-6-PD deficiency and observed clinically with serum bilirubin evaluations as indicated for hyperbilirubinemia. On day 3, blood was sampled for COHb, total hemoglobin (tHb), and a mandatory serum bilirubin determination. COHb, determined by gas chromatography, was expressed as percentage of tHb and corrected for inspired carbon monoxide (COHbc). DNA was analyzed for the G-6-PD Mediterranean563T mutation and for the variant UGT1A1 gene.

RESULTS

The cohort included 54 G-6-PD-deficient heterozygotes, 19 deficient homozygotes, and 112 normal homozygotes. More heterozygotes (12/54, 22%; relative risk: 2.26; 95% CI: 1.07-4.80) and deficient homozygotes (5/19, 26.3%; relative risk: 2.68; 95% CI: 1.05-6.90) developed hyperbilirubinemia, than did normal homozygotes (11/112, 9.8%). Third-day serum bilirubin values that were obtained from 144 neonates were significantly higher in both heterozygotes (11.2 +/- 3. 7 mg/dL [192 +/- 64 micromol/L]) and G-6-PD-deficient homozygotes (12.0 +/- 3.0 mg/dL [206 +/- 52 micromol/L]) than in the G-6-PD normal homozygotes (9.4 +/- 3.4 mg/dL [160 +/- 58 micromol/L). In contrast, COHbc values were higher only in G-6-PD-deficient homozygotes (0.74% +/- 0.14%) and not in heterozygotes (0.69% +/- 0. 19%, not statistically significant), compared with control values (0. 63% +/- 0.19%). High COHbc values were not a prerequisite for the development of hyperbilirubinemia in any of the G-6-PD genotypes. A greater incidence of hyperbilirubinemia was found among the G-6-PD-deficient heterozygotes, who also had the variant UGT1A1 gene, in both heterozygous (6/20, 30%) and homozygous (4/8, 50%) forms, than was found in their counterparts with the normal UGT1A1 gene (2/26, 7.7%). This effect was not seen in the G-6-PD normal homozygote group. A color reduction screening test for G-6-PD deficiency identified only 20.4% (11/54) of the heterozygotes.

CONCLUSIONS

We showed that G-6-PD-deficient heterozygotes, categorically defined by DNA analysis, are at increased risk for neonatal hyperbilirubinemia. The screening test that was used was unable to detect most heterozygotes. Increased bilirubin production was not crucial to the development of hyperbilirubinemia, but presence of the variant UGT1A1 gene did confer increased risk.

Bilirubin levels in the acute hemolytic crisis of G6PD deficiency are related to Gilbert's syndrome

In this study we analyzed the effect of the (TA)7 polymorphism of the UGT1A gene associated with Gilbert's syndrome in G6PD-deficient subjects during an acute hemolytic crisis (fabic crisis). DNA from 44 subjects originating from the same geographic area in Sardinia was analyzed for the UGT1A promoter polymorphism. The increase of unconjugated bilirubin level during fabic crisis and its relationship with UGT1A polymorphism was evaluated. The UGT1A (TA)7 TATA box variant was found in 9/44 (21%) of the G6PD deficient subjects examined. The median value for unit of increase of bilirubin (mg/dl)/unit of decrease of hemoglobin (g/dl) was higher in variant homozygous than in heterozygous and normal subjects. These findings imply a contribution of the UGT1A polymorphism associated to Gilbert's syndrome to development of the hyperbilirubinemia in G6PD deficient subjects during acute hemolytic anemia.

Bilirubin conjugation, reflected by conjugated bilirubin fractions, in glucose-6-phosphate dehydrogenase-deficient neonates: a determining factor in the pathogenesis of hyperbilirubinemia

BACKGROUND AND OBJECTIVE

Glucose-6-phosphate dehydrogenase (G-6-PD) deficiency is frequently associated with neonatal hyperbilirubinemia, which in severe cases may cause kernicterus and death. Because G-6-PD-deficient individuals frequently undergo acute, trigger-induced hemolytic episodes, increased hemolysis has frequently been implied in the pathogenesis of this neonatal hyperbilirubinemia. However, in Sephardic Jewish G-6-PD-deficient neonates, the rate of hemolysis, reflected by blood carboxyhemoglobin values corrected for inspired carbon monoxide, has been shown to be elevated, not only in those who developed hyperbilirubinemia, but also, to a similar extent, in those who remained only moderately jaundiced. Because at any point, serum total bilirubin values reflect a balance between bilirubin production on the one hand and bilirubin conjugation and elimination on the other, we suspected bilirubin conjugation to be a key factor in the pathogenesis of the hyperbilirubinemia. Physiologically, a fraction of conjugated bilirubin refluxes from the hepatocyte to the serum, and accurate determination of serum conjugated bilirubin fractions can be used to mirror intrahepatocytic bilirubin. Using this principle, we previously demonstrated a decreased diconjugated bilirubin fraction in hyperbilirubinemic G-6-PD-deficient neonates compared with hyperbilirubinemic G-6-PD-normal controls, suggesting diminished bilirubin conjugation. This conjugated bilirubin pattern probably reflects the recently described interaction between G-6-PD deficiency and the variant promoter for the gene encoding the bilirubin conjugating enzyme UDP glucuronosyltransferase, as seen in Gilbert's syndrome. Therefore, we postulated that efficiency of bilirubin conjugation is a crucial factor in the development of hyperbilirubinemia in G-6-PD-deficient neonates. We hypothesized that those G-6-PD-deficient neonates who develop hyperbilirubinemia would have decreased bilirubin conjugation ability, whereas those with a more efficient conjugating system would have a lesser degree of bilirubinemia.

METHODS

Term, healthy, male, G-6-PD-deficient neonates with no other obvious predisposing cause for hyperbilirubinemia were selected at random when their serum diazo total bilirubin values ranged from 171 to 254 micromol/L (10-14.9 mg/dL). At this point, simultaneous with the diazo bilirubin determination, serum was collected and frozen for high-performance liquid chromatography (HPLC) measurement of serum bilirubin fractions. The infants were followed clinically and with serum diazo bilirubin determinations until they either did not exceed a serum diazo bilirubin value of 254 micromol/L (14.9 mg/dL) (nonhyperbilirubinemic) or until bilirubin values rose above this level (hyperbilirubinemic), by a process of self-selection. A method of alkaline methanolysis, followed by reverse-phase HPLC, was used to measure unconjugated bilirubin and the mono- and diconjugated fractions of serum conjugated bilirubin. Total HPLC bilirubin and total conjugated bilirubin values were calculated from these measured bilirubin fractions. Patients also were classified according to the serum total conjugated bilirubin value as low bilirubin conjugators (serum total conjugated bilirubin less than median) or as high bilirubin conjugators (serum total conjugated bilirubin greater than median). The data were analyzed by comparing serum conjugated bilirubin fractions between the hyperbilirubinemic and nonhyperbilirubinemic groups and the risk of developing hyperbilirubinemia in the low bilirubin conjugators, relative to that of the high bilirubin conjugators.

RESULTS

Neonates were sampled at 53 +/- 12 and 58 +/- 12 hours for the subsequently hyperbilirubinemic and nonhyperbilirubinemic groups, respectively (NS). Initial (ie, at the time of sampling) serum total diazo bilirubin values (mean +/- SD) were almost identical for the subsequently hyperbilirubinemic and nonhyperbilirubinemic groups (214 +/

Gilbert syndrome and glucose-6-phosphate dehydrogenase deficiency: a dose-dependent genetic interaction crucial to neonatal hyperbilirubinemia

Severe jaundice leading to kernicterus or death in the newborn is the most devastating consequence of glucose-6-phosphate dehydrogenase (EC 1.1.1.49; G-6-PD) deficiency. We asked whether the TA repeat promoter polymorphism in the gene for uridinediphosphoglucuronate glucuronosyltransferase 1 (EC 2.4.1.17; UDPGT1), associated with benign jaundice in adults (Gilbert syndrome), increases the incidence of neonatal hyperbilirubinemia in G-6-PD deficiency. DNA from term neonates was analyzed for UDPGT1 polymorphism (normal homozygotes, heterozygotes, variant homozygotes), and for G-6-PD Mediterranean deficiency. The variant UDPGT1 promoter allele frequency was similar in G-6-PD-deficient and normal neonates. Thirty (22.9%) G-6-PD deficient neonates developed serum total bilirubin >/= 257 micromol/liter, vs. 22 (9.2%) normals (P = 0.0005). Of those with the normal homozygous UDPGT1 genotype, the incidence of hyperbilirubinemia was similar in G-6-PD-deficients and controls (9.7% and 9.9%). In contrast, in the G-6-PD-deficient neonates, those with the heterozygous or homozygous variant UDPGT1 genotype had a higher incidence of hyperbilirubinemia than corresponding controls (heterozygotes: 31.6% vs. 6.7%, P < 0.0001; variant homozygotes: 50% vs. 14.7%, P = 0.02). Among G-6-PD-deficient infants the incidence of hyperbilirubinemia was greater in those with the heterozygous (31.6%, P = 0.006) or variant homozygous (50%, P = 0.003) UDPGT1 genotype than in normal homozygotes. In contrast, among those normal for G-6-PD, the UDPGT1 polymorphism had no significant effect (heterozygotes: 6.7%; variant homozygotes: 14.7%). Thus, neither G-6-PD deficiency nor the variant UDPGT1 promoter, alone, increased the incidence of hyperbilirubinemia, but both in combination did. This gene interaction may serve as a paradigm of the interaction of benign genetic polymorphisms in the causation of disease.