Relative red blood cell enzyme levels as a clue to the diagnosis of pyruvate kinase deficiency

Abstract

Evaluation of two patients with transfusion dependent anemia revealed RBC pyruvate kinase to be 33% and 41% of the mean normal value, with normal or high values of other RBC enzymes. Parental PK activities were just below normal in three of four of the parents. Subsequent DNA analysis revealed both patients to be compound heterozygotes for PKLR gene mutations, two of which are previously undescribed. Borderline low pyruvate kinase activities with increased in other RBC enzyme activities should prompt consideration of measurement of parental enzyme activities, and confirmation by DNA analysis if available.

Diagnosis of Pyruvate Kinase Deficiency

“…Of interest, heterozygous parents, who are clinically and hematologically normal, may exhibit mildly decreased levels of pyruvate kinase, suggesting biochemical heterozygosity. As done by Kager et al., and earlier by Titapiwatanakun et al., this observation can be leveraged in the study of parents of transfusion‐dependent children to direct further diagnostic testing …”

“…Rarely, affected patients have dysfunctional thermolabile enzyme variants without enzyme deficiency . In PK deficiency, detection of elevated upstream glycolytic intermediates contributes to the certainty of the diagnosis, but in clinical practice, this is seldom done . When needed, erythrocytes can be separated by density centrifugation and pyruvate kinase levels determined.…”

A novel PKLR gene mutation identified using advanced molecular techniques

“…First, the PK levels depend on the age of RBCs, because younger RBCs have higher PK levels. The presence of reticulocytosis and large quantities of nucleated RBCs in the peripheral blood when hemolysis occurs also produce higher levels of PK . Next, multiple and frequent transfusions can obscure enzymatic defects.…”

“…The presence of reticulocytosis and large quantities of nucleated RBCs in the peripheral blood when hemolysis occurs also produce higher levels of PK. 19 Next, multiple and frequent transfusions can obscure enzymatic defects. Finally, the PK isozyme in white blood cells cannot be totally eliminated from the sample, which can influence the detection of the PK levels.…”

Biocomputing for Portable, Resettable, and Quantitative Point‐of‐Care Diagnostics: Making the Glucose Meter a Logic‐Gate Responsive Device for Measuring Many Clinically Relevant Targets

“…Utilizing this assay, the input PK can be sensitively detected as low as 0.18 U/mL (Figure 2c), which is well below the clinic cut-off range of 2.2–4.4 U/mL for the diagnosis of PK deficiency. [15] To demonstrate that the NOT gate design can be generally applied to detection of other targets, another NOT gate was constructed for the detection of citrate, an important metabolite related to many diseases, such as cancer, [16] using citrate lyase (CL) and malate dehydrogenase (MDH) as the logic units. As shown in Figure 2b, a new enzyme cascade is triggered to convert citrate into oxaloacetate and then into NADH consumption.…”