Red cell enzymopathies in the newborn. II. Inherited deficiencies of red cell enzymes.

The mature, anueleate human red cell is incapable of synthesizing en­ zymes and is dependent upon anaerobic metabolism to m eet its energy requirements. Thus, inherited red cell enzyme deficiencies of the glycolytic pathway often result in chronic nonspherocytic hemolytic anemia (CNSHA). The hexosemonophosphate (HMP) shunt is normally relatively inactive and enzyme deficiences, such as G-6-PD deficiency, usually result in episodic hemolysis secondary to oxidative stress. Deficiency of G-6-PD is the most common red cell enzymopathy. Pyruvate kinase (PK) deficiency is the most common enzyme deficiency of the glycolytic pathway, followed in fre­ quency by glucose phosphate isomerase (GPI) deficiency. Other glycolytic enzyme deficiencies are rare. Red cell phosphofructokinase deficiency can be associated with muscle weakness; triosephosphate isomerase (TPI) and phosphoglycerate kinase deficiencies with neurologic abnormalities. Since its original description, pyrimidine-5'-nucleotidase deficiency has been rec­ ognized with greater frequency as a cause of CNSHA. Enolase, glyceraldehyde phosphate dehydrogenase, and lactic dehydrogenase deficiencies are not associated with hemolysis. The newborn with CNSHA can develop anemia and significant jaundice in the first 24 hrs of life. Precise diagnosis may be difficult owing to the volume of blood required and the laboratory facilities available. Screening tests for G-6-PD, GPI, TPI, and PK deficiencies and the red cell concentra­ tion of 2,3-diphosphoglycerate can all be done with small amounts of blood obtained with a heel puncture. Data obtained for red cell glycolytic intermediates and quantitative en­ zyme assays must be compared to normal values for neonates since red cells at birth and during the first two months of life have unique metabolic