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Tuesday, May 21, 2013

SUPPORT SICKLE CELL AWARENESS - 3

So far I have written generally on sickle cell disease, how it comes about and the types concentrating on sickle cell anemia, it's symptoms and the main causing element of it; erythrocytes. I think we are making progress.
Knowing that the hemoglobin carries the genes through which SCA is inherited from both parents, I would like to briefly explain it.



AS and AS
male
A
S
female
A
AA
AS
S
AS
S






 AS and SS
male
A
S
female
S
AS
SS
S
AS
SS















 AA and SS
male
A
A
female
S
AS
AS
S
AS
AS






 AS and AA
male
A
S
female
A
AA
AS
A
AA
AS












 AA and AA
male
A
A
female
A
AA
AA
A
AA
AA




 SS and SS
male
S
S
female
S
SS
SS
S
SS
SS


















 
AA(yellow) - normal hemoglobin
AS(orange) - sickle cell trait/carrier
SS(red) - sickle cell anemia


For diagrams 3, 5 and 6, every pregnancy is expected 100% HbAS offspring, HbAA offspring and HbSS offspring respectively.
For diagram 4, in each pregnancy a 50% chance of HbAS offspring or 50% chance of HbAA offspring is expected.
For diagram 2, each pregnancy has a chance of 50% HbAS offspring or 50% chance of HbSS offspring.
For diagram 1, each and every pregnancy has a 25% chance of HbAA offspring, 25% chance of HbSS offspring or a 50% chance of HbAS offspring.

A lot of us make the mistake of thinking "if we have 4 children only one will be HbSS and one will be HbAA while the other two will be HbAS". It's wrong! The genetic ratio is for each and every time a couple will be having a child. If for instance a couple plan on having 3 kids and he is HbAS while she is HbSS every time she gets pregnant, that particular fetus could either have inherited a 50% probability of being HbAS or 50% chance of being HbSS. That means after all the kids have been born (not at once of course), the three of them could all be HbAS or HbSS or 2 out of 3 could be HbAS while 1 is HbSS or 1 could be HbAS while 2 could be HbSS. There is no saying this amount will come out with HbSS or this amount won't have HbSS. It remains unknown. However, modern improvement in medical sciences has come up with forms of prenatal diagnostic techniques that are used to determine if a fetus has any form of genetic disorder before it is born. 

-Chorionic Villus Sampling (CVS) entails the use of samples from the placental tissue of the fetus from as early as 8 weeks till 12 weeks of gestation. CVS is used for testing chromosomal abnormalities and other specific genetic disorders (including SCD/SCA) especially when the parents are known carriers of the defective gene and/or there is a family history of a known genetic disorder.
As with everything in life, there are risks involved in such tests and some exemptions such as women with known HIV statuses because the chances of the fetus getting infected is greatly increased. Not to mention it is expensive.

-Pre-implantation Genetic Diagnosis (PGD) as the name suggests the process is used to test for or detect genetic disorders before implanting the embryo into the uterus of the lady. This means it is carried out via in vitro fertilization. A greater advantage of this process is that it totally eliminates the option of pregnancy termination otherwise known as abortion  and also more chances of being sure about having offsprings that will be free of any form of genetic disorder, in our case sickle cell. This also comes along with it's own risks and is equally really expensive.
I think I should briefly point out that in vitro fertilization enables for more than one fertilization at a time from the same couples which allows for greater chances of having healthy embryos. Fertilized embryos can also be stored by freezing however it usually does not have a successful survival birth rate.

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