A logical approach to the investigation of red cell enzymopathies.

This relatively rare group of disorders may cause quite marked morbidity and occasionally be life-threatening. As their inheritance is largely known accurate information in one family member has obvious benefits to other family members as well as the patient. The identification of the defect is dependent on an accurate clinical story which can be used to guide both the use and the interpretation of the various laboratory tests available. From the clinical aspect the enzymopathies can be divided into various broad groups. First, those involving the main glycolysis which produces the red cell's energy requirements in the form of ATP. Defects of this pathway generally cause a non-spherocytic haemolytic anaemia. Second, those involving the pentose phosphate shunt which maintains the redox potential of the cell necessary for its protection against oxidant stress. The commonest enzyme deficiency world wide, G6PD, is in this pathway and is characterized by stress-induced haemolytic crises. Third, defects of the various linked reactions. The most important of these are the methaemoglobin reductases which catalyse the reduction of methaemoglobin to functional haemoglobin and the enzymes in the Rapoport-Luebering shunt which can modulate the 2,3-DPG level. Whilst defects of these metabolic pathways make up the majority of cases associated with haemolysis, defects of other enzymes, on the whole less critical to the red cell's survival, must occasionally be considered. The red cell, because of its relatively easy availability, can be used as a 'biopsy tool' in the diagnosis of some systemic disorders in which the red cell enzymopathy is not the main feature of the disease. Such considerations are particularly important owing to the technological advances that have occurred in the last 10-15 years which have enabled correct assignment of an increased number of difficult cases. Not only is it possible to characterise the variant enzymes more accurately but it is now possible to have a 'metabolic window' on the red cell and examine it for the derangements of metabolism that characterise the various enzyme deficiencies.

Mosaic tetrasomy 8p: molecular cytogenetic confirmation and measurement of glutathione reductase and tissue plasminogen activator levels.

We report the case of a 5-year-old girl with severe developmental disabilities, skeletal anomalies, hypotonia, rectal atresia, malrotation of the intestine, horseshoe kidney, vesicoureteric reflux, and minor facial anomalies. Conventional cytogenetic techniques suggested that she had a mosaic 46,XX/47,XX,+i(8p) constitution, and the identity of the isochromosome was confirmed by in situ hybridization and chromosome painting. Polymorphic DNA markers are consistent with the i(8p) having arisen as the result of a segregation error and centromere misdivision at the second maternal meiotic division. The i(8p) was seen in 17/25 (68%) lymphocytes at the age of one month but had declined to 31/100 (31%) cells by the age of 5 years. At this time the i(8p) was seen in 30/68 (44%) cultured skin fibroblasts. The proposita had an approximately twofold increase in red cell glutathione reductase activity but a normal level of tissue-plasminogen activator. These enzyme results are consistent with the known localisation of the glutathione reductase gene on the short arm of chromosome 8 but suggest that the tissue-plasminogen activator gene may map outside this region.

Lead poisoning: clinical, biochemical, and haematological aspects of a recent outbreak.

The clinical, biochemical, and haematological aspects of a recent outbreak of lead poisoning, in which exposure was related to the oxyacetylene cutting of red lead painted ironwork, were investigated. Initial suspicion was raised when a blood film showed punctate basophilia which remains a simple and useful method of picking up lead toxicity. Estimations of blood lead concentration and conventional laboratory data confirmed the diagnosis. Although there was prominent punctate basophilia, spectrophotometric analysis showed only negligible accumulation of pyrimidine-5'-nucleotides despite severe suppression of pyrimidine-5'-nucleotidase activity. The pattern of the red cell glycolytic intermediates, investigated for the first time, suggested that lead may also affect glycolysis at the hexokinase step. Once the diagnosis was made intravenous chelation treatment was begun with a rapid improvement in symptoms. Long term follow up is required to assess any sequelae of intoxication. These cases emphasise the classic features of lead poisoning, and despite the currently available diagnostic tests, lead intoxication may still go unrecognised unless a thorough occupational history is taken.

A reappraisal of the gamma-glutamylcysteine synthetase activity in haemolysates from normal erythrocytes by two different methods.

gamma-Glutamylcysteine synthetase catalyses the combination of L-glutamate and L-cysteine to form gamma-glutamylcysteine with a stoichiometric conversion of ATP to ADP and inorganic phosphate (Pi). During the estimation of this enzyme in haemolysates from normal erythrocytes it was found that the Pi released was more than the amount of gamma-glutamylcysteine synthesised. Furthermore, the activity estimated by analysing either product was higher than the corresponding values reported in the literature. An investigation into these discrepancies resulted in improvements of the assay methods which produced two substantially different normal ranges for the gamma-glutamylcysteine synthetase activity in haemolysates: one derived from the Pi released and the other from the gamma-glutamylcysteine synthesised during the enzymatic reaction.

The effect of pH upon human transferrin: selective labelling of the two iron-binding sites.

The influence of pH changes upon the iron-binding properties of transferrin was investigated in the absence of chelating agents. The effects were demonstrated by spectrophotometry, gel filtration, and by studies of the intermolecular transfer of 59Fe from transferrin to conalbumin. At pH values below 6.7, diferric transferrin readily loses iron. The monoferric molecule, which is relatively resistant to acid dissociation, is preferentially formed. A temporary reduction of pH provides a simple method for selectively attaching iron to one metal-binding site, and allows double isotopic labelling of the transferrin molecule. This technique may permit further investigation of the physiological properties of the two iron-binding sites.

Normal glutathione content and some related enzyme activities in the fetal erythrocytes.

Pure fetal blood was obtained by direct-vision fetoscopy from 66 fetuses at 17-24 weeks gestation. The concentration of GSH and the activities of the enzymes gamma-glutamylcysteine synthetase (GCS), glutathione synthetase (GS), glutathione reductase (GR) and glutathione peroxidase (GPx) were analysed by established techniques to find the normal ranges for this gestational age. The ranges were relatively narrow and could serve as reference values for the prenatal diagnosis of defects in the GSH metabolism of erythrocytes. The results were compared with those obtained from 38 normal adults and with published values on neonatal blood. In the case of GR a comparison was also made with maternal blood. In comparison with adults, fetal erythrocytes showed higher GSH concentration and GCS activity and lower GS and GPx activities. This pattern resembled that found in neonatal erythrocytes except for the GCS activity, which was higher in the fetal cells. Furthermore the differences between fetal and adult erythrocytes were more pronounced than those between neonatal and adult cells. The GR activity of fetal erythrocytes was also higher than that of either normal adult or maternal blood. This difference, however, was reduced to an insignificant level when the enzyme was activated in vitro by flavin adenine dinucleotide (FAD) because of a relatively low per cent activation of the GR in the fetal erythrocytes.

Red cell glycolytic intermediates in normal, anaemic and transfused human fetuses.

Normal fetal ranges for red cell glycolytic intermediates at 18-24 weeks gestation, which are useful as reference values for the prenatal diagnosis of erythroenzymopathies, were established for the first time. Characteristic increases in glucose-6-phosphate (G6P), fructose-6-phosphate (F6P) and particularly fructose-1,6-diphosphate (FDP) suggest that there is no metabolic block at the phosphofructokinase (PFK) step of glycolysis as previously suggested by others for premature infants on the first day of life. Neither reticulocytosis nor anaemia consistently led to further increases in the early metabolites as occurs in adults. However, very large increases in G6P, F6P and particularly FDP may occur independently of anaemia and reticulocytosis. This suggests that activation of hexokinase (HK) and/or PFK can take place as in adults but the stimulus is probably different to adults. The 2,3-DPG in normal fetuses is higher than in adults and increases still further in anaemic fetuses with or without transfusion of adult blood. The pattern of intermediates found in the fetus suggests that the controlling mechanism for the increased 2,3-DPG may be an in vivo relative preponderance of PFK activity over that of pyruvate kinase (PK) rather than regulation of HK as proposed for adult subjects with anaemia or high altitude hypoxia.

Normal activities of glycolytic enzymes in the fetal erythrocytes.

Pure fetal blood was obtained by direct-vision fetoscopy from 24 fetuses at 17-24 weeks' gestation. The activities of 14 glycolytic enzymes in the erythrocytes were analysed by established techniques to find the normal ranges of activity for this gestational age. The results were compared with those obtained from 24 normal adults and with published values on neonatal blood. The activities of most enzymes in fetal erythrocytes were found to be higher and the relative pattern of activity different from those of adult or neonatal blood. The ranges were relatively narrow and can serve as reference values for the prenatal diagnosis of erythrocytic enzymopathies. Also, the activities of the glycolytic enzymes will provide a basis for the understanding of erythrocyte metabolism in the fetus.

Red cell 3-phosphoglycerate level as a diagnostic aid in pyruvate kinase deficiency.

A case of pyruvate kinase (PK) deficiency is described in which the diagnosis was aided by measurement of the 3-phosphoglycerate (3PG) concentration. Review of the literature on the levels of red cell metabolites in 52 families with PK deficiency confirmed that a rise in 3PG is a valuable indicator of a functional deficiency of PK. Estimation of 3PG is relatively easy (and accurate). Furthermore, reticulocytosis, which sometimes makes the diagnosis of PK deficiency more difficult, has minimal effect on the level of 3PG in comparison with all other glycolytic intermediates or PK activity.

Normal levels of ATP, total nucleotides and activities of three enzymes related to nucleotide metabolism in fetal erythrocytes.

Pure fetal blood was obtained by direct-vision fetoscopy from 30 fetuses at 17-23 weeks gestation. The erythrocyte concentrations of ATP and total nucleotides and the activities of the enzymes pyrimidine-5'-nucleotide nucleosidase (Pyr5N), phosphoribosylpyrophosphate (PRPP) synthetase and adenylate kinase (AK) were analysed by established techniques to find the normal ranges for this gestational age. The ranges were relatively narrow and could serve as reference values for the prenatal diagnosis of defects in nucleotide metabolism. The results from the fetal erythrocytes were compared with the corresponding values from the maternal blood collected and analysed concurrently. The ATP and total nucleotide concentrations and the activity of Pyr5N in the fetal cells were substantially higher than those of the maternal blood. The activities of PRPP synthetase and AK were much lower. The significance of these findings is discussed.

Prenatal diagnosis of a red-cell enzymopathy: triose phosphate isomerase deficiency.

A child with triose phosphate isomerase deficiency was born to nonconsanguineous parents, and died at 13 months of age. The parents were both found to be heterozygous for this enzyme deficiency. At a subsequent pregnancy, analysis of fetal red blood cells obtained by cordocentesis at 19 weeks' gestation enabled prenatal diagnosis of the heterozygous state. This technique may allow diagnosis of other red-cell enzymopathies during the second trimester.

2,3-Diphosphoglycerate in normal, anaemic and transfused human fetuses.

1. The effect of anaemia and transfusion with adult blood on fetal 2,3-diphosphoglycerate levels was investigated by studying fetal blood from 45 normal pregnancies at 17-42 weeks of gestation and in 34 pregnancies complicated by erythroblastosis fetalis. 2. In normal fetuses, 2,3-diphosphoglycerate concentration was higher than in adults and did not change significantly with gestational age. 3. In erythroblastotic fetuses, there was a significant negative correlation between 2,3-diphosphoglycerate concentration and haemoglobin concentration. 4. When adult blood was transfused into the fetal circulation, 2,3-diphosphoglycerate concentration reached similar levels to that found in untransfused fetuses after allowing for the severity of anaemia.