In heterozygotes, the activity of glucose phosphate isomerase in erythrocytes is 40-60% of the norm, the disease is asymptomatic. In homozygotes, the enzyme activity is 14-30% of the norm, the disease occurs as hemolytic anemia. The first manifestations of the disease can be observed already in the neonatal period - pronounced jaundice, anemia, splenomegaly are noted.