In a
last few weeks Sickle cell trait seems to have caught up the attention of regional
as well as national media. A regional radio channel broadcasted news that says
there has been an increase in population with Sickle cell trait in Amaravati district
of Maharashtra. A piece in a newspaper says Sickle Cell Anaemia (SCA) is
prevalent in 10 per cent of Chattisgarh population. One more news-report
published informs that a full-fledged research center for SCA shall be set up
in Odisha soon.
A write-up
in a fortnightly magazine says that according
to a recently published study, by 2050 almost half a million babies are likely
to be born with SCA compared to 305,800 in 2010. Nigeria, the Democratic Republic
of Congo and India will be the most affected.
I have sympathy for those
who suffer because of this trait directly or indirectly; however one must
acknowledge the fact that this is an evidence that we humans are still evolving
by natural selection.
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| Sickle shaped cells in blood |
SCA, a hereditary blood disorder,
occurs due to mutation in the haemoglobin gene. However, fatal SCA is
manifested only in homozygotes individuals, who have received the mutant gene
from both the parents. The heterozygotes individuals, who have received the
mutant gene from only one parent, are not anaemic and can lead normal lives. These are called carriers.
Considering their number in the affected population may give a false impression to a
layman.
It was found in Africa that where
the population of heterozygotes for the sickle gene is as high as 40 per cent
in some districts, which fall in the falciparum malaria-prone zone. Falciparum
is the most severe form of malaria. And, people with sickle cell trait are much
more resistant to malaria because cells infected by malarial parasite tend to
sickle and collapse, interfering with the development of the parasite. Thus, in
areas where falciparum malaria is prevalent, sickle-cell heterozygotes are
fitter than either the sickell cell homozygote, who dies in childhood of
anaemia, or the normal homozygote, who may die of malaria, also usually in
childhood.
The
nature had a plan, when it preserved a mutant gene which is lethal in
homozygotes by selection. The selection helped in increasing fitness of
heterozygotes in the malarial environment.
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