Hemoglobin variants

Globins

Feature	α	β	δ	γ
Main period	All	Late fetal to Adult	Infancy to Adult	Embryonic, Fetal, Neonatal
Partner in Hb	β, γ, δ	α	α	α
Major Hb form	All	HbA	HbA₂	HbF
O₂ affinity	Variable	Normal	Normal	High
Disease link	α-thal.	β-thal., SCD	None serious	Therapeutic
Key Distinctive Feature	Only globin present in all major hemoglobins; essential for life	Principal adult hemoglobin chain; most clinically relevant	Almost identical to β but less abundant; forms minor adult HbA₂	Highest O₂ affinity; critical for fetal-maternal O₂ transfer

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HbF: has significantly higher oxygen affinity than adult hemoglobin A. This allows fetal hemoglobin to extract more oxygen from the mother's adult hemoglobin in the placenta, providing the developing fetus with an adequate supply of oxygen.
HbS: Point mutation in the β-globin gene resulting in the replacement of glutamic acid by valine
HbC: Point mutation in the β-globin gene resulting in the replacement of glutamic acid by lysine

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Normal hemoglobin consists primarily of hemoglobin A (HbA), which migrates rapidly toward the positive electrode (anode) because of its negative charge.
Hemoglobin S (HbS) is an abnormal type of hemoglobin in which a nonpolar amino acid (valine) replaces a negatively charged amino acid (glutamate) in the beta globin chain. This amino acid replacement decreases the negative charge on the HbS molecule, which causes HbS to move more slowly toward the anode.
- Glutamate (-) → Valine (=)
Similarly, hemoglobin C (HbC) has a glutamate residue replaced by lysine in the beta globin chain. Because lysine is a positively charged amino acid, HbC has even less total negative charge than HbS and moves even more slowly toward the anode. Both HbC and HbS result from missense mutations, a type of mutation in which a single base substitution results in a codon that codes for a different amino acid.
- Glutamate (-) → Lysine (+)