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At a glance

It is a rare, but most common hereditary glycolytic enzyme defect that results in nonspherocytic hemolytic anemia.

Synonyms

Pyruvate Kinase Deficiency of Erythrocytes; Pyruvate Kinase Liver Type Deficiency.

History

First described in 1952 by British hematologist, Sir John V. Dacie (1912-2005), in patients with congenital hemolytic anemia who presented with hereditary spherocytosis. However, in the more recently described anemia, it is shown that the osmotic fragility is normal and spherocytes not encountered.

Incidence

The prevalence rate of a heterozygous carrier is approximately 1 to 3% and the prevalence of confirmed cases has been estimated at about 1:20,000 in the white population births. Pyruvate kinase deficiency (PKD) affects both genders equally and occurs in all races (a high incidence has been reported in Amish people from Pennsylvania as a result of a founder effect). Internationally, PKD has been reported in Northern Europe and Japan. The prevalence in Germany is reported at 1% and Hong Kong 3%. In the United Kingdom, the prevalence is 3.2 cases per million population. PKD has been shown to have a protective effect against replication of the malaria parasite in human red cells, although it is not clear whether PK-LR mutant alleles are more prevalent in malaria endemic areas.

Genetic inheritance

Autosomal recessive. Over 200 different mutations have been described in patients with PKD.

Pathophysiology

It is caused by mutations in the PKLR gene (pyruvate kinase expressed in liver and red blood cells [RBCs]), which has been mapped to chromosome 1q22 and encodes the L (liver) and R (red cells) pyruvate kinase isozymes. The mature erythrocytes have neither a nucleus nor mitochondria, and therefore depend entirely on anaerobic glycolysis as a source of energy. Pyruvate kinase (PK) catalyzes the conversion of phosphoenolpyruvate to pyruvate and is one of three rate-limiting kinases (together with hexokinase and phosphofructokinase) in the Embden-Meyerhof pathway, which is responsible for adenosine triphosphate (ATP) production by anaerobic glycolysis. On the one hand, this defect results in accumulation of intermediate and various glycolytic metabolites in the erythrocyte upstream of the enzymatic block; on the other hand, these RBCs lack the products downstream in the pathway (lactate and ATP). ATP is required to maintain erythrocyte transmembranous electrolyte concentration gradients (mainly potassium) across the cellular membrane, hydration, and flexibility of the RBC. Consequently, the lack of ATP results in loss of potassium, dehydration, and rigidity of the cellular membrane, and, finally, in premature destruction of the erythrocytes in spleen and liver. A shunt in the glycolytic pathway unique to the erythrocyte (Rapoport-Luebering shunt) is responsible for the two- to threefold increase in intracellular 2,3-DPG concentration, and hence a marked right shift in the oxygen dissociation curve of hemoglobin with decreased affinity of hemoglobin for oxygen.

Diagnosis

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