Other Cell Membrane Disorders As Inherited Disorders Of The Erythrocytes

Hereditary elliptocytosis (HE)

This is a specific autosomal dominant disorder where mild hemolysis occurs, but may remain unnoticed in about 90% cases.

Acanthocytosis

Acanthocytes are abnormal erythrocytes showing projections of variable width and length on their surface. They are seen in abetalipoprotenemia and severe liver disorders

Red cell enzymopathy

Glucose-6-phosphate dehydrogenase (G-6-PD) deficiency is a type of such erythrocyte disorder. It is prevalent in different parts of the world, commonly in the Mediterranean population. In India for example, the incidence varies from 1 to 20% in different ethnic groups. Three common variants of G-6-PD have been identified. These are G-6-PD Kerala, G-6-PD West Bengal and G-6-PD Jammu. At present, over 100 isoenzymes of G-6-PD have been recognized. The G-6-PD deficiency gives a partial protection against falciparum malaria.

It is a sex-lined phenomenon being transmitted from mother to son. 50% of the sons are affected while the heterozygous female may show only slightly lower enzyme values. The G-6-PD deficiency finds full expression in hemizygote males and homozygote females. Clinical features depend on the severity of enzyme deficiency and the racial patterns.

Class I: Enzyme activity is below 10% and this results in chronic hemolysis

Class II: Enzyme activity is below 10% but there is no chronic hemolysis, eg, G-6-PD-B.

Class III: Functional activity 10 to 60%. Here hemolysis occurs only after exposure to drugs or infections eg, G-6-PD-A.

Class IV: Normal functional activity.

Class V: Increased activity.

Classes IV and V are of no clinical significance. The Indian variant usually produces hemolysis on exposure to several drugs and infections. Drug-induced hemolysis may present as a life-threatening disorder in such subjects. Rarely neonatal disorder may occur. Though any drug can produce hemolysis in these enzyme-deficient subjects, the common offenders are anti-malarials, sulfa drugs, analgesics, antibodies, other anti-bacterial agents, and vitamin K.

Laboratory findings

Severe anemia may result. Red cells may show Heinz bodies before the onset of hemolysis. These are refractile inclusions which are seen in the erythrocyte in the wet unstained preparation. They are indistinguishable by the Romanowski stains, since they stain uniformly with the surrounding hemoglobin. Hemoglobinuria may develop and this may result in renal failure. Reticulocytes are increased. Red cell morphology is generally normal. Estimation of the enzymes helps in establishing the diagnosis. Since reticulocytes are generally rich in G-6-PD, the enzyme activity may be normal in the presence of active reticulocytosis. In such cases, the enzyme assay should be repeated after the reticulocytosis has subsided.

Course

Hemolysis in the majority of G-6-PD deficiency patients is a self-limiting phenomenon and in the majority, it tends to subside as reticulocytosis occurs.

Therapy

Mild cases are self-limniting and demand only withdrawal of the offending drugs. In severe caes, blood transfusion may be required. Renal failure should be managed on its own merits. Subjects who are G-6-PD deficient should be informed of the condition to prevent further recurrence.