Pyruvate kinase deficiency

Definition

Pyruvate kinase deficiency is an inherited deficiency of the enzyme pyruvate kinase, which is used by red blood cells. Without this enzyme, red blood cells break down too easily, resulting in low levels of these cells (Hemolytic anemia).

Causes, incidence, and risk factors

Pyruvate kinase deficiency is transmitted as an autosomal recessive trait, which means that a child must get the defective gene from both parents to develop the disorder.

There are many different types of enzymatic defects of the red blood cell which can cause hemolytic anemia. Pyruvate kinase deficiency is the second most common cause of enzymatic-related hemolytic anemia. (G-6-PD deficiency is the number one cause.)

Pyruvate kinase deficiency may produce mild or severe hemolysis and anemia. Problems may first appear in the newborn as prolonged jaundice and anemia. Older children may be pale (due to anemia) and have intermittent episodes of jaundice. Occasionally, it is not discovered until adulthood in mild cases.

Although pyruvate kinase deficiency is found in people of all ethnic backgrounds, certain populations, such as the Amish, have a somewhat higher incidence.

Symptoms

• A family history of pyruvate kinase deficiency
  
• Pallor
  
• Jaundice
  
• A yellowing of the whites of the eyes (icterus)
  
• Fatigue, Lethargy caused by anemia
  
• Recurrent gallstones
  

Signs and tests
During a physical exam, the doctor will look for an Enlarged spleen.

Tests include the following:

• CBC showing anemia with normocytic (not pale) red blood cells
  
• macrocytosis (large red blood cells)
  
• pyruvate kinase activity shows deficient levels of this enzyme in red blood cells
  
• high levels of bilirubin in the blood
  
• low levels of haptoglobin in the blood
  
• increased osmotic fragility or red blood cells may not be present
  
• high fecal urobilinogen
  
• genetic testing for mutation in the pyruvate kinase gene
  

Blood transfusions may be needed for severe anemia. Removal of the spleen (splenectomy) may help to reduce the destruction of red blood cells; however, this should not necessarily be performed as it does not help in all cases. In newborns with dangerous levels of jaundice, an exchange transfusion is likely to be recommended.