Hereditary persistence of fetal hemoglobin (HPFH) associated with beta-thalassemia is characterized by high hemoglobin (Hb) F levels and an increased number of fetal-Hb-containing-cells. The disease is Monarch Disease Ontology term MONDO_0018749 (hereditary persistence of fetal hemoglobin-beta-thalassemia syndrome). Also known as: HPFH-beta-thalassemia syndrome.