Hemoglobin C disease is a hereditary or genetic condition that occurs in one out of 5,000 to 10,000 African American individuals. If a child has Hemoglobin C disease, both parents have hemoglobin C trait. Hemoglobin C trait occurs in 2-3% of all African Americans. Hemoglobin C trait is harmless - you do not have the disease - you are just a ...