Pyrimidine 5'-Nucleotidase (P5N) Deficiency P5N is a key enzyme in the catabolism of nucleotides arising from the degradation of nucleic acids that takes place in the final stages of red cell maturation. How exactly its deficiency causes HA is not well understood, but a highly distinctive feature of this condition is a morphologic abnormality of the red cells known as basophilic stippling. The condition is rare, but it probably ranks third in frequency among red cell enzyme defects (after G6PD deficiency and PK deficiency). The anemia is lifelong, of variable severity, and may benefit from splenectomy. Familial Hemolytic Uremic Syndrome. | Chapter 101. Hemolytic Anemias and Anemia Due to Acute Blood Loss Part 13 Pyrimidine 5 -Nucleotidase P5N Deficiency P5N is a key enzyme in the catabolism of nucleotides arising from the degradation of nucleic acids that takes place in the final stages of red cell maturation. How exactly its deficiency causes HA is not well understood but a highly distinctive feature of this condition is a morphologic abnormality of the red cells known as basophilic stippling. The condition is rare but it probably ranks third in frequency among red cell enzyme defects after G6PD deficiency and PK deficiency . The anemia is lifelong of variable severity and may benefit from splenectomy. Familial Hemolytic Uremic Syndrome HUS This disorder is unique because now that its basis has been elucidated we can clearly see that hemolysis is due to an inherited defect but this is external to red cells. HUS is defined as a microangiopathic hemolytic anemia with fragmented erythrocytes in the peripheral blood smear thrombocytopenia usually mild and acute renal failure. An infection is usually the trigger of the syndrome which tends to recur. When it does the prognosis is serious. Although familial HUS is rare studies of affected members from more than 100 families have revealed numerous mutations in any of three complement regulatory proteins membrane cofactor protein factor H and factor I. It is thought that when complement is activated through the alternative pathway following damage to endothelial cells in the kidney one of the results will be brisk hemolysis. Thus the much more common Shiga toxin-related HUS can be regarded as a phenocopy of familial HUS. Acquired Hemolytic Anemia Mechanical Destruction of Red Cells Although red cells are characterized by the remarkable deformability that enables them to squeeze through capillaries narrower than themselves thousands of times in their lifetime there are at least two situations in which they succumb to shear if not to wear and tear the result .
