PYRUVATE KINASE DEFICIENCY

Pyruvate Kinase Deficiency — the most common glycolytic enzyme defect causing chronic hemolytic anemia, now with the first FDA-approved disease-modifying therapy (mitapivat, 2022) where the PKLR genotype determines treatment response.

Whole genome sequencing identifies all PKLR variants — determining whether mitapivat (Pyrukynd) will activate the patient's specific mutant pyruvate kinase enzyme or whether the variant produces a protein that cannot be pharmacologically rescued.

PKLR

About this condition

Hereditary Hemolytic Anemia — Glucose-6-Phosphate Isomerase Deficiency & Pyruvate Kinase Deficiency

Pyruvate kinase deficiency (PKD) is the most common glycolytic enzyme defect causing hereditary non-spherocytic hemolytic anemia (HNSHA), affecting approximately 1 in 20,000 people worldwide. It is caused by autosomal recessive pathogenic variants in PKLR (chromosome 1q22), encoding the liver/red cell isoform of pyruvate kinase. PK deficiency impairs glycolytic ATP production in mature red blood cells (which lack mitochondria and depend entirely on glycolysis for energy), causing chronic extravascular hemolysis with anemia, reticulocytosis, jaundice, splenomegaly, and gallstones.

Clinical severity varies widely — from fully compensated hemolysis (normal hemoglobin maintained by increased reticulocyte production) to transfusion-dependent severe anemia requiring regular red blood cell transfusions from infancy. Hydrops fetalis occurs in the most severe forms. Iron overload is a major long-term complication, developing in both transfusion-dependent and non-transfusion-dependent patients due to inappropriate intestinal iron absorption driven by chronic hemolysis and ineffective erythropoiesis. Splenectomy partially ameliorates the anemia but does not cure it and carries lifelong infection risk.

Mitapivat (Pyrukynd, Agios Pharmaceuticals) was FDA-approved in 2022 for hemolytic anemia in adults with PKD — the first disease-modifying therapy for any glycolytic enzymopathy. Mitapivat is an oral allosteric activator of pyruvate kinase that binds to and stabilizes the PK tetramer, increasing catalytic activity of the mutant enzyme. Treatment increases hemoglobin, reduces markers of hemolysis, and in transfusion-dependent patients can reduce or eliminate transfusion requirements. However, mitapivat responsiveness depends on the specific PKLR genotype — variants that produce no protein (null alleles) cannot be pharmacologically activated. Molecular PKLR genotyping is required for treatment planning.

Mitapivat can only activate PK variants that produce a structurally intact but functionally impaired enzyme. PKLR null variants (producing no protein) are non-responsive. Genotype determines whether the drug has a molecular target to work on.

Gene locus: PKLR (1q22)

PKD was previously managed only with splenectomy and transfusion support. Mitapivat changes this — but eligibility requires PKLR molecular genotyping to determine whether the specific variant can be pharmacologically rescued.

Mitapivat responsiveness depends on whether the PKLR variant produces an activatable enzyme — molecular genotyping makes this prediction

PKLR missense variants that produce a structurally intact but kinetically impaired pyruvate kinase enzyme are candidates for mitapivat activation — the drug stabilizes the PK tetramer and partially restores catalytic efficiency. In contrast, PKLR nonsense, frameshift, or splice variants that produce no stable protein cannot be pharmacologically rescued. Patients homozygous for null alleles are predicted non-responders, while patients compound heterozygous for a missense and null allele have intermediate response potential (one allele can be activated). This genotype-response relationship is clinically validated and directly determines treatment planning.

Iron overload in PKD develops even without transfusions — molecular diagnosis triggers proactive iron monitoring

Unlike thalassemia, where iron overload is primarily transfusion-driven, PKD patients develop iron overload from increased intestinal iron absorption mediated by suppressed hepcidin. Non-transfusion-dependent PKD patients can develop significant hepatic iron deposition and eventual cirrhosis without proactive monitoring and chelation therapy. Molecular PKD diagnosis — rather than a vague diagnosis of 'chronic hemolytic anemia' — ensures that the patient is entered into appropriate iron surveillance protocols (regular ferritin, liver MRI T2*) and receives chelation when indicated.

Pyruvate Kinase Deficiency — the most common glycolytic enzyme defect causing chronic hemolytic anemia, now with the first FDA-approved disease-modifying therapy (mitapivat, 2022) where the PKLR genotype determines treatment response.

Hereditary Hemolytic Anemia — Glucose-6-Phosphate Isomerase Deficiency & Pyruvate Kinase Deficiency

PKD was previously managed only with splenectomy and transfusion support. Mitapivat changes this — but eligibility requires PKLR molecular genotyping to determine whether the specific variant can be pharmacologically rescued.

Mitapivat responsiveness depends on whether the PKLR variant produces an activatable enzyme — molecular genotyping makes this prediction

Iron overload in PKD develops even without transfusions — molecular diagnosis triggers proactive iron monitoring

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