Stroke risk in siblings with sickle cell anemia.

Cerebrovascular disease is a common cause of morbidity in sickle cell anemia (HbSS): approximately 10% of patients have a clinical stroke before 20 years of age, and another 22% have silent infarction on magnetic resonance imaging. The phenotypic variation among patients with HbSS suggests a role for modifier genes and/or environmental influences. To assess the familial component of clinical stroke in HbSS, we estimated the prevalence of clinical stroke among all patients and among HbSS sibling pairs at 9 pediatric centers. The sample included 3425 patients with sickle cell disease who were younger than 21 years, including 2353 patients with HbSS. The stroke prevalence was 4.9% for all genotypes; 7.1% for patients with HbSS; 1.1% for patients with HbSbeta(o) thalassemia; 0.6% for patients with Sbeta(+) thalassemia; and 0% for patients with HbSC. In 207 sibships, more than 1 child had HbSS. There were 42 sibships in which at least 1 sibling had a stroke, and in 10 of the 42, 2 siblings had a stroke. A permutation test indicated that the number of families in which 2 children had strokes was larger than the number expected if strokes were randomly distributed among children in sibships (P =.0012). There was no difference in stroke prevalence based on sex, nor was the mean age at stroke presentation significantly different between singletons and sibships with stroke. We conclude that there is a familial predisposition to stroke in HbSS. Attempts to identify genetic modifiers should be initiated with family-based studies.