EFFECTS OF THALASSEMIA AND MICROCYTOSIS ON THE HEMATOLOGIC AND VASOOCCLUSIVE SEVERITY OF SICKLE-CELL-ANEMIA

  • 1 January 1984
    • journal article
    • research article
    • Vol. 63  (6) , 1353-1360
Abstract
The characteristic clinical heterogeneity of sickle cell anemia (HbSS) may be, in part, a result of its interactions with .alpha.-thalassemia. Although .alpha.-thalassemia clearly affects some hematologic features of HbSS, its role in modulating the vasoocclusive severity of disease is not clear. The incidence of painful episodes, acute chest syndrome, aseptic bone necrosis and leg ulcers was examined in 3 patient groups with sickle cell disease: 2147 patients over age 2 yr, stratified according to mean corpuscular volume (MCV); 183 patients selected on the basis of microcytosis and elevated HbA2, on whom globin biosynthesis studies were done; and 125 patients who had .alpha.-globin genotype assigned by restriction endonuclease gene mapping. When patients were stratified by MCV, there was a reciprocal relationship between HbA2 levels and MCV, reflecting the presence of patients with .beta..degree. and .alpha.-thalassemia in the low MCV groups. The erythrocyte indices and HbA2 levels in patients classified as HbSS-.alpha.-thalassemia, by either globin synthesis studies or gene mapping, were very similar to those previously reported by others. Neither microcytosis, .beta..degree., or .alpha.-thalassemia appeared to provide any clear protection from the vasoocclusive complication evaluated, and the prevalence of aseptic necrosis was increased in patients with microcytosis over age 20 yr and in groups with .alpha.-thalassemia. The effects of a reduced MCV and mean corpuscular Hb concentration (MCHC), of possible benefit by themselves, when accompanied by a reduction in hemolysis and rise in Hb concentration, as in HbSS-.alpha.-thalassemia, may cause sufficient rise in blood viscosity in critical vascular beds to impair blood flow and negate any amelioration of vasoocclusive complications in HbSS.