A young, African American girl has run a long race in a late morning gym class. Soon afterwards she feels unusually fatigued and, because she remains lethargic during the early afternoon, she is sent home from school. She is drowsy and has difficulties following directions and answering questions. She says she is tired and her muscles feel weak. She complains of generalized pain in her torso and muscles of her arms and legs. She exhibits shortness of breath. Her skin is slightly bluish in her fingertips/palms/lips. The laboratory analysis of a blood sample reveals Low hematocrit, low level of hemoglobin. Stained blood smear shows that red blood cells are normocytic but that numerous cells hace a hooked shape. Electophoresis of the blood indicates an abnormal form of hemoglobin. What type of diesase or condition is she suffering from?