Hereditary non-spherocytic haemolytic anaemia due to red blood cell glutathione synthetase deficiency in four unrelated patients from Spain: clinical and molecular studies

Glucose-6-Phosphate Dehydrogenase Deficiency and Neonatal Hyperbilirubinemia: Insights on Pathophysiology, Diagnosis, and Gene Variants in Disease Heterogeneity

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a prevalent condition worldwide and is caused by loss-of-function mutations in the G6PD gene. Individuals with deficiency are more susceptible to oxidative stress which leads to the classical, acute hemolytic anemia (favism). However, G6PD deficiency in newborn infants presents with an increased risk of hyperbilirubinemia, that may rapidly escalate to result in bilirubin induced neurologic dysfunction (BIND). Often with no overt signs of hemolysis, G6PD deficiency in the neonatal period appears to be different in the pathophysiology from favism. This review discusses and compares the mechanistic pathways involved in these two clinical presentations of this enzyme disorder. In contrast to the membrane disruption of red blood cells and Heinz bodies formation in favism, G6PD deficiency causing jaundice is perhaps attributed to the disruption of oxidant-antioxidant balance, impaired recycling of peroxiredoxin 2, thus affecting bilirubin clearance. Screening for G6PD deficiency and close monitoring of affected infants are important aspects in neonatal care to prevent kernicterus, a permanent and devastating neurological damage. WHO recommends screening for G6PD activity of all infants in countries with high prevalence of this deficiency. The traditional fluorescent spot test as a screening tool, although low in cost, misses a significant proportion of cases with moderate deficiency or the partially deficient, heterozygote females. Some newer and emerging laboratory tests and diagnostic methods will be discussed while developments in genomics and proteomics contribute to increasing studies that spatially profile genetic mutations within the protein structure that could predict their functional and structural effects. In this review, several known variants of G6PD are highlighted based on the location of the mutation and amino acid replacement. These could provide insights on why some variants may cause a higher degree of phenotypic severity compared to others. Further studies are needed to elucidate the predisposition of some variants toward certain clinical manifestations, particularly neonatal hyperbilirubinemia, and how some variants increase in severity when co-inherited with other blood- or bilirubin-related genetic disorders.

A Rare Cause of Neonatal Hemolytic Anemia: Glutathione Synthetase Deficiency

BACKGROUND

Isolated hemolysis or hemolytic anemia and 5-oxoprolinuria are 2 distinct medical conditions in the clinical spectrum associated with glutathione synthetase deficiency.

CLINICAL OBSERVATION

A 1-day-old female baby presented with anemia and respiratory distress. Her hemoglobin level was 9.5 g/dL and the total serum bilirubin level was 5.6 mg/dL. Metabolic acidosis was detected in her blood gas analysis. Metabolic acidosis recurred despite treatment and further investigation was required. Her 5-oxoproline level was 3815 mmol/mol creatinine in urine organic acid analysis, and a homozygous mutation [p.R125H (c.374G>A)] was found in the glutathione synthetase gene.

CONCLUSIONS

GSD has been observed in very few patients and is rarely considered in the differential diagnosis of hemolytic anemia in newborns.

Recurrent Isolated Neonatal Hemolytic Anemia: Think About Glutathione Synthetase Deficiency

Hemolytic anemia (HA) of the newborn should be considered in cases of rapidly developing, severe, or persistent hyperbilirubinemia. Several causes of corpuscular hemolysis have been described, among which red blood cell enzyme defects are of particular concern. We report a rare case of red blood cell enzyme defect in a male infant, who presented during his first months of life with recurrent and isolated neonatal hemolysis. All main causes were ruled out. At 6.5 months of age, the patient presented with gastroenteritis requiring hospitalization; fortuitously, urine organic acid chromatography revealed a large peak of 5-oxoproline. Before the association between HA and 5-oxoprolinuria was noted, glutathione synthetase deficiency was suspected and confirmed by a low glutathione synthetase concentration and a collapse of glutathione synthetase activity in erythrocytes. Moreover, molecular diagnosis revealed 2 mutations in the glutathione synthetase gene: a previously reported missense mutation (c.[656A>G]; p.[Asp219Gly]) and a mutation not yet described in the binding site of the enzyme (c.[902T>C]; p.[Leu301Pro]). However, 15 days later, a control sample revealed no signs of 5-oxoprolinuria and the clinical history discovered administration of acetaminophen in the 48 hours before hospitalization. Thus, in this patient, acetaminophen exposure allowed the diagnosis of a mild form of glutathione synthetase deficiency, characterized by isolated HA. Early diagnosis is important because treatment with bicarbonate, vitamins C and E, and elimination of trigger factors are recommended to improve long-term outcomes. Glutathione synthetase deficiency should be screened for in cases of unexplained newborn HA.

Alternative RNA splicing in expression of the glutathione synthetase gene in human cells

Ubiquitous free radical production occurs continuously in cells and tissues. Glutathione is the most abundant mammalian antioxidant, and is synthesized by glutathione synthetase (GSS). Therefore, GSS plays an important role in defending the cell against reactive oxygen species. The expression of GSS has been studied in human cells; however, sequence information about alternative splicing variants of GSS mRNA has not been reported. In the present study, we identified a novel alternative splicing variant (ASV) of the GSS gene in 10 human normal tissues and five human cancer cell lines. The deleted transcript of GSS was characterized by an in-frame deletion of 333 bp, corresponding to the complete loss of exons 4 and 5. Thus this GSS ASV causes protein truncation. We quantified the mRNA of GSS ASV in human normal tissues using real-time PCR. The ASV was detected in colon, kidney, lung, liver, placenta, peripheral blood and uterus, but not in heart, skeletal muscle and spleen tissue. Our results provide a basis for more detailed studies on the regulation of GSS, and for further evaluation of this and other possible roles of GSS. Understanding the regulation of GSS expression is very important for the development of new strategies for controlling the development of GSH-based redox homeostasis.

Genotype, enzyme activity, glutathione level, and clinical phenotype in patients with glutathione synthetase deficiency

Glutathione synthetase (GS) deficiency is a rare autosomal recessive disorder. The clinical phenotype varies widely, and nearly 30 different mutations in the GSS gene have been identified. In the present study, genotype, enzyme activity, metabolite levels and clinical phenotype were evaluated in 41 patients from 33 families. From some of the patients, data on glutathione (GSH) levels and gamma-glutamylcysteine levels in cultured fibroblasts were also available. Twenty-seven different mutations were found: 14 missense, 9 splice, 2 deletions, 1 insertion and 1 nonsense mutation. Twenty-three patients were homozygous and 18 were compound heterozygous. The moderate and severe clinical phenotypes could not be distinguished based on enzyme activity, GSH or gamma-glutamylcysteine levels in cultured fibroblasts. However, in fibroblasts, the residual GS activity was correlated with the GSH level. All mutations causing frameshifts, premature stop codons or aberrant splicing were associated with moderate or severe clinical phenotypes including haemolytic anaemia, 5-oxoprolinuria, and (in several forms) neurodevelopmental signs. The data indicate that additional genetic or environmental factors modify at least the moderate and severe phenotypes and that the clinical classification given to the patients may be influenced by variation in follow-up. The type of mutation involved can, to some extent, predict a mild versus a more severe phenotype.

Physiological and pathological aspects of GSH metabolism

The antioxidant glutathione is found in low levels in diseases in which increasing evidence implicate oxidative stress in the development of the disease, for example retinopathy of prematurity, necrotizing enterocolitis, bronchopulmonary dysplasia, patent ductus arteriosus and asthma. Glutathione is metabolized in the gamma-glutamyl cycle, which involves six different enzymes. The synthesis of glutathione is a two-step process in which the first step is catalysed by gamma-glutamylcysteine synthetase and the second step by glutathione synthetase. Glutathione synthetase deficiency is an autosomal recessive disease and the most common inborn error of the gamma-glutamyl cycle. Approximately 25% of patients with hereditary glutathione synthetase deficiency die during childhood. Patients present with a clinical picture ranging from compensated haemolytic anaemia to a complex disorder with additional symptoms like 5-oxoprolinuria, metabolic acidosis and central nervous system impairment. Even though the correlation between phenotype and genotype in these patients is complex, an indication of the phenotype can be based on the type of mutation involved. Also, there is a correlation between the glutathione synthetase activity and the level of glutathione in cultured fibroblasts. Inborn errors have also been described in three additional steps of the y-glutamyl cycle, namely gamma-glutamyl-transpeptidase, 5-oxoprolinase and gamma-glutamylcysteine synthetase.

CONCLUSION

The range of disorders in patients with inborn errors in the metabolism of glutathione illustrates the intricate metabolism of glutathione and its involvement in numerous essential processes in the cell. By studying these patients, further insight into the functions and metabolism of glutathione can be achieved.

Human hereditary glutathione synthetase deficiency: kinetic properties of mutant enzymes

Patients with hereditary glutathione synthetase deficiency suffer from haemolytic anaemia, 5-oxoprolinuria, metabolic acidosis, recurrent bacterial infections and various degrees of central nervous system dysfunction. To investigate the molecular basis of the mutations associated with this disease, seven naturally occurring missense mutations [L188P (Leu188-->Pro), D219A, D219G, Y270C, Y270H, R283C and P314L] were expressed using a His-tagged, Escherichia coli-based expression system. Effects of the mutations on kinetic properties, including negative co-operative binding of gamma-glutamyl substrate, were evaluated. The mutation P314L did not have any major effect on these parameters and was classified as a neutral mutation. The remaining mutations decreased V(max) to 2-27% of wild-type activity. Negative co-operativity for gamma-gluABA (L-gamma-glutamyl-L-alpha-aminobutyric acid) was abolished in five mutant recombinant enzymes, whereas for one mutant enzyme, this co-operativity changed from negative to positive. The structural consequences of the mutations were interpreted on the basis of the known structure of the wild-type enzyme.

A novel missense mutation in the gamma-glutamylcysteine synthetase catalytic subunit gene causes both decreased enzymatic activity and glutathione production

Gamma-glutamylcysteine synthetase (gamma-GCS) catalyzes the first and rate-limiting step in glutathione (GSH) biosynthesis: the adenosine triphosphate (ATP)-dependent ligation of glutamate and cysteine. gamma-GCS consists of a catalytic (gamma-GCSH) and modifier (gamma-GCSL) subunit. Hereditary deficiency of gamma-GCS has been reported in a small number of patients and is associated with low erythrocyte levels of gamma-GCS and GSH leading to hemolytic anemia. Here we report a novel gamma-GCSH mutation, isolated from the cDNA of 2 related patients diagnosed with gamma-GCS deficiency. Each was found to be homozygous for a C>T missense mutation at nucleotide 379, encoding for a predicted Arg127Cys amino acid change. Computerized structure modeling identified that the mutated amino acid lies within a cleft on the protein surface of gamma-GCSH, and the border of this cleft was shown to contain Cys249, an evolutionarily conserved residue that has been proven to lie near the binding site of gamma-GCSH. Transfection studies showed that the mutation is associated with decreased GSH production, and binding studies using purified recombinant protein showed that the mutant protein has markedly decreased enzymatic activity compared to wild type.