Sickle Cell Anaemia: Foetal Homozygous Recessive Not Affected

[e-diot]

i've been asked to explain the observation of sickle cell anaemia which is caused by a recessive point mutation in the beta chain of adult haemoglobin, but foetus homozygous recessive is not affected.

why is that? i have been told that foetus has haemoglobin gamma not beta and therefore can't get affected.

i thought that if u had homozygous recessive though, then u would get the disease??

 

[adrenaline]

Sickle cell disease includes the homozygous HBSS but other sickeling syndromes include double heterozygous conditions such as HBS-betathalasemia, HbSC etc.) All of them are associated with structurally abnormal hemoglobin molecule that polymerize under reduced oxygen conditions or dehydration. The fetal hemoglobin F that we are born with does not seem to polymerize as much or is protected from sickeling, but the switch from HBF to HbS occurs after the first few months of life. Some people have a hereditary persistance of fetal hemoglobin (higher concentrations) or have other genetic variants of sickle cell with elevated HbF levels. In general, these patients have mild or minimal disease.