Hemoglobinopathies are autosomal codominant traits—thus, com- pound heterozygotes who inherit a different abnormal mutant allele from each parent exhibit composite features of each. For example, patients inheriting sickle β thalassemia exhibit features of β thalas- semia and sickle cell anemia. The α chain is present in HbA, HbA 2 , and HbF; α-chain mutations thus cause abnormalities in all three. The α-globin hemoglobinopathies are symptomatic in utero and after birth because normal function of the α-globin gene is required throughout gestation and adult life. In contrast, infants with β-globin hemoglo- binopathies tend to be asymptomatic until 3–9 months of age, when HbA has largely replaced