Fetal hemoglobin

Fetal hemoglobin (HbF) is a type of hemoglobin that is present in the fetus and newborn. It is composed of two alpha and two gamma chains (α2γ2), which distinguishes it from adult hemoglobin (HbA), which consists of two alpha and two beta chains (α2β2). HbF has a higher affinity for oxygen than adult hemoglobin, which facilitates the transfer of oxygen from the maternal to the fetal circulation.

Structure and Function

Fetal hemoglobin is structurally different from adult hemoglobin due to the presence of gamma chains instead of beta chains. This difference in structure allows HbF to bind oxygen more tightly than adult hemoglobin. The higher oxygen affinity of HbF is crucial for fetal development, as it allows efficient uptake of oxygen from the placenta, where the partial pressure of oxygen is lower than in the lungs.

Comparison of oxygen saturation curves for HbA and HbF

The oxygen dissociation curve of HbF is shifted to the left compared to that of adult hemoglobin, indicating its higher affinity for oxygen. This property is essential for the fetus to extract oxygen from the maternal blood supply.

Genetic Regulation

The production of fetal hemoglobin is controlled by genes located on chromosome 11. The gamma globin genes (HBG1 and HBG2) are active during fetal development but are usually silenced after birth as the beta globin genes (HBB) become more active.

Genetic regulation of hemoglobin production postnatally

In some individuals, the production of fetal hemoglobin persists into adulthood, a condition known as hereditary persistence of fetal hemoglobin (HPFH). This can be beneficial in certain hemoglobinopathies, such as sickle cell disease and beta-thalassemia, where increased levels of HbF can ameliorate symptoms.

Clinical Significance

Fetal hemoglobin plays a significant role in certain blood disorders. In sickle cell disease, the presence of HbF can reduce the sickling of red blood cells and alleviate symptoms. Similarly, in beta-thalassemia, increased levels of HbF can compensate for the lack of functional beta chains.

Sickle cells in sickle cell disease

Therapeutic strategies to induce the production of fetal hemoglobin in adults are being explored as potential treatments for these disorders. Drugs such as hydroxyurea have been used to increase HbF levels in patients with sickle cell disease.

Also see

• Hemoglobin
• Sickle cell disease
• Beta-thalassemia
• Hereditary persistence of fetal hemoglobin