This study will explore how people with sickle cell disease (SCD) develop a complication called pulmonary hypertension (PHTN), a serious disease in which blood pressure in the lungs is higher than normal. PHTN is also caused by HIV, hepatitis C and schistosomiasis. Patients who have both SCD and one of these other infections may develop more severe PHTN. The number of Nigerians with SCD who also have PHTN is not known, nor is the cause of PHTN in this population. This study will examine genetic material in people with and without SCD to determine whether certain genes will allow doctors to predict which patients with SCD are likely to develop PHTN.