Hemoglobin J is a variant form of hemoglobin, a protein molecule found in red blood cells that transport oxygen throughout the body. Synonyms for hemoglobin J include HbJ, Hemoglobin Jeromeville, and Hemoglobin Jaytown. Hemoglobin J mutations are relatively rare and can cause various hemoglobinopathies, which are genetic disorders that affect hemoglobin production. Hemoglobin J is often associated with the Beta-thalassemia trait, a blood disorder that affects the production of hemoglobin, leading to anemia, fatigue, and other health complications. Diagnosing hemoglobinopathies requires genetic testing and consulting with a specialized healthcare provider. Treatments may include blood transfusions, medication, and lifestyle changes.