To the Editor.
—Lippman et al1 reported a high prevalence of mitral valve prolapse in patients with sickle cell disease. Their finding of a prevalence rate of 21% in patients homozygous for sickle cell hemoglobin (HbS) is at variance with data from our recently completed study of cardiac function in patients with sickle cell anemia. Their method of case selection and their conclusions merit comment.Their study group consisted of 57 patients, 46 homozygous for HbS and 11 with sickle cell disease, who were drawn from a laboratory registry of patients with HbS. Of the 92 patients identified as having HbS, approximately a third were unavailable or unwilling to participate in the study. Sample bias is inherent in such a nonrandom selection process. It is unlikely that their estimate of the prevalence of mitral valve prolapse derived from this small subgroup of patients with sickle cell disease is representative