In healthy adults, fetal hemoglobin (HbF) is present at residual levels (less than 0.06% of total hemoglobin) with over 20-fold variation. Ten to fifteen percent of adults fall within the upper tail of the distribution and have HbF levels between 0.8% and 5%, a condition referred to as heterocellular hereditary persistence of fetal hemoglobin Although these HbF levels are modest in otherwise healthy individuals, interaction of heterocellular HPFH with beta-thalassemia (see 613985) or sickle cell disease (SS; 603903) can increase HbF output in these individuals to levels that are clinically beneficial (Menzel et al., 2007).
For a general phenotypic description and a discussion of loci that may affect fetal hemoglobin levels, see HBFQTL1 (141749). [from
OMIM]