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Erythrocyte enzymopathies 

Erythrocyte enzymopathies

Erythrocyte enzymopathies

Ernest Beutler

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date: 23 April 2017

Numerous enzymes, including those of the hexose monophosphate pathway and glycolysis, are active in the red cell. They are required for the generation of ATP (needed to supply energy for sodium extrusion) and the reductants NADH and NADPH, necessary to maintain haemoglobin in its active ferrous atomic state, as well as for the integrity of sulphydryl groups present on essential proteins. 2,3-diphosphoglycerate (2,3-DPG), an intermediate of glucose metabolism, is a key regulator of the affinity of haemoglobin for oxygen, and accessory enzymes are also active for the synthesis of glutathione, disposal of oxygen free radicals, and nucleotide and nucleotide metabolism.

Clinical features—general considerations

With the exception of heavy metal poisoning, most red-cell enzyme deficiency disorders are inherited conditions, which may (1) cause haematological disorders, including most commonly haemolytic anaemias, but rarely polycythaemia or methaemoglobinaemia; (2) mirror important metabolic disorders, without producing haematological problems, making them of diagnostic value, e.g. galactosaemia; (3) be of no known consequence.

Genetics—one-half of the normal activity of red-cell enzymes is generally sufficient for normal function, hence most haemolytic anaemias due to red-cell enzyme deficiencies occur as autosomal recessive or sex-linked disorders.

Diagnosis of red-cell enzymopathies

With rare exceptions it is impossible to differentiate the enzymatic defects from one another by clinical or routine laboratory methods. Diagnosis depends on the combination of (1) accurate ascertainment of the family history; (2) morphological observations—these can determine whether haemolysis is present, rule out some causes of haemolysis (e.g. hereditary spherocytosis), and diagnose pyrimidine 5′‎-nucleotidase deficiency (prominent red cell stippling); (3) estimation of red-cell enzyme activity; and (4) DNA analysis.

Specific red-cell abnormalities that may cause haemolytic anaemia

These include (1) glucose-6-phosphate dehydrogenase (G6PD) deficiency—see Chapter 22.5.12; (2) pyruvate kinase deficiency; (3) glucosephosphate isomerase deficiency; (4) pyrimidine 5′‎-nucleotidase deficiency—which may also induced by exposure to environmental lead; (5) triosephosphate isomerase deficiency.

Acknowledgements: This is manuscript 18838-MEM from The Scripps Research Institute. Supported by the Stein Endowment Fund.

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