The purpose of this study is to see if the investigators can better understand asthma when it occurs in a person who has sickle cell disease. The investigators will do this by taking a blood, urine, and saliva sample. The blood and urine samples will be analyzed for chemicals and DNA (genes). Certain genes can cause patients to have sickle cell disease or asthma. The investigators will use the saliva sample for future studies to compare the results from the blood testing with saliva. The investigator's long-term goal is to make sure people who have asthma and sickle cell disease are getting the best asthma treatments. The investigator's hypothesis is that the analysis of the blood, urine and saliva using a method called, metabolomics, may identify a unique asthma signature in children with sickle cell disease which may lead to targeted treatments.