Outcome in hemoglobin SC disease: A four‐decade observational study of clinical, hematologic, and genetic factors

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Abstract
Over the past 40 years, we observed 284 subjects with hemoglobin SC disease (Hb SC) for 2,837 person‐years. We examined the association of the course of clinical events with hematologic and genetic factors. The mean entry age was 21 years, although 15% entered before one year of age. The mean Hb concentration was 11.3 g/dL, the mean fetal hemoglobin was 2.5%, and the mean MCV was 84.4 fL. Twenty‐five subjects died at a median age of 37 years. Chronic organ‐specific complications occurred in 112 subjects (39.4%), with advanced retinopathy in 65 subjects (22.9%) and osteonecrosis (avascular necrosis) in 42 subjects (14.8%). We identified the β‐globin haplotypes in 82 subjects and the α‐gene status in 79. Twenty‐nine percent had α‐thalassemia‐2. The βCI haplotype was present in 85.4%. We found a decreased incidence of retinopathy in the βCI subjects compared to the non‐βCI subjects (33% vs. 67%; P = 0.049) with a later mean onset age (29 years vs. 21 years; log‐rank test, P= 0.026). We also found a consistent pattern of decreased morbidity in subjects who had α‐thalassemia‐2 in comparison to those who did not. We found a reduced risk of chronic organ‐specific complications (log‐rank test, P= 0.003), lower incidence of sickle crisis (48% vs. 80%, P= 0.001), later onset of gallbladder disease (age of onset: 55 years vs. 34 years; P= 0.055), and lower risk of osteonecrosis (log‐rank test, P= 0.024). Our findings suggest that Hb SC subjects who have not inherited α‐thalassemia‐2 might benefit from erythrocyte rehydration therapy. Am. J. Hematol. 70:206–215, 2002.