Main objective (200 children): To evaluate the prevalence of elevated blood pressure (former pre-hypertension) and hypertension (including masked hypertension) in children with sickle cell disease. Secondary objectives (60 children): to evaluate the prevalence of loss of nocturnal decrease in blood pressure (dipping); to evaluate arterial stiffness (pulse wave velocity: PWV) and vascular resistance (Augmentation Index, AI) in the different groups: normal, pre-hypertension and hypertension; to evaluate the cardiac sympathovagal balance by studying heart rate variability (HRV) in the three groups: normal, pre-hypertension and hypertension; to evaluate arterial in the three groups: normal, pre-hypertension and hypertension; to evaluate whether the absence of nocturnal dipping is or is not an associated factor of abnormal arterial stiffness, systemic vascular resistance, sympathovagal balance or baroreflex by comparison of subjects with normal dipping versus abnormal dipping.
