Identity of the α-Chains of the Minor Human Hæmoglobin Components A ₂ and A ₂′ with the α-Chains of Human Hæmoglobin A and F

Abstract

THE occurrence of a minor hæmoglobin component (A ₂′ or B ₂), which is related to the well-known hæmoglobin fraction A ₂, has recently been described^1,2. This variant, found in families of a Negro community of James Island, is characterized by a very low mobility at an alkaline pH. The electrophoretic pattern (at pH 8.8) of the hæmoglobin of a person heterozygous for this abnormality, shows a major hæmoglobin fraction (A ₀), the fast moving fraction (A ₁), the slow moving hæmoglobin A ₂, and the hæmoglobin A ₂′ with a still lower mobility. The hæmoglobin A ₂ and hæmoglobin-A ₂′ are present in equal amounts (0.8–1.2 per cent), the sum of both being equal to the percentage of hæmoglobin A ₂ present in the blood of a normal individual. The hæmoglobin A ₂′ has also been demonstrated in cases with sickle cell trait², indicating that the two abnormalities (‘double A ₂ spot’ and ‘the presence of the abnormal hæmoglobin S’) are controlled by a different pair of alleles. In some cases of thalassæmia trait both hæmoglobin A ₂ fractions were found to be increased by a factor of two^1,2, the ‘double A ₂ spot’ being contributed by one parent and the thalassæmia trait by the other parent.