Fetal haemoglobin synthesis
© 1976 Ciba Foundation. All rights reserved. The factors involved in the switch from fetal to adult haemoglobinproduction during normal human development are not yet worked out. Availableevidence suggests that control is mediated both at the chromosomal and cellularlevel. There is good evidence that critical areas of the chromosome carrying thelinked γ-, δ- and β-chain genes are involved in the suppression of γ-chain synthesisafter the first few months of life. There is also evidence that the number of cellscontaining haemoglobin F in normal adults is genetically determined. Availabledata are compatible with the notion that hypertrophy of the latter cell populationmay account for the raised levels of haemoglobin F in β-thalassaemia and sicklecellanaemia where there is a marked selection of γ -chain producing cells. Themechanism of the switching of haemoglobin types is completely unknown butthe fact that more F cells than usual are produced in some pregnancies suggeststhat it may be hormonal..