hereditary persistence of fetal hemoglobin-sickle cell disease syndrome (MONDO_0016672) is a rare, genetic, hemoglobinopathy characterized by generally mild clinical phenotype, high fetal hemoglobin levels and mild microcytosis and hypochromia. In some cases, acute sickle cell disease manifestations were reported, namely acute chest syndrome and acute pain crisis. The genotype is characterized by the combination of an HbS and HbF allele; symptoms depend on the degree of HbF:HbS expressivity with patients with more than 35% pancellular HbF expression being asymptomatic. Symptomatic patients have heterocellular expression of HbF. Also known as: HPFH-sickle cell disease syndrome.