Genetics; Sickle Cell Disease

Genetics; Sickle Cell Disease

Introduction

Sickle cell anemia is a severe type of hemolytic anemia that develops as a result of an individual inheriting a sickle hemoglobin gene. The inherited sickle hemoglobin gene causes the hemoglobin molecule within the person’s circulation to become defective. The sickle hemoglobin then assumes a crystal like formation whenever there is exposure to reduced oxygen tensions.  The normally biconcave disc-shaped RBC assumes a sickle shape. The cut form compromises the ability of the RBC to carry oxygen to various tissues since the oxygen carrying capacity has been reduced (Anglin, 2015). The new sickle shape is rigid and cannot allow for the RBCs to maneuver themselves into small blood vessels like capillaries, further hampering delivery of oxygen into the tissues of the body beyond the capillaries. Another effect of sickling is that the life cycle of the RBC severely reduces. What was normally between approximately one hundred and twenty days falls to ten to twelve days.

In this paper, however, the focus will be on discussing the genetics around the inheritance of the sickle gene between family members. The discussion will be based on a case study of Marsha and Clement a married couple who are both carriers of the sickle cell disease.

Sickle cell anemia is inherited by children as an autosomal recessive disease. The implication is that the gene has no linkage to the sex chromosomes. There is, therefore, a possibility that the illness could be passed from a parent carrying it to either their male or female children. For a child to get sickle cell anemia he or she must have inherited one sickle cell gene from the mother and another sickle cell gene from the father. The child will thus have two sickle cell genes.

In the cases where the child has only inherited one sickle cell gene from either the father or the mother, the inheritance is termed as the sickle cell trait. The condition is synonymously termed as the carrier state. Patients should be taught that the sickle cell trait does not cause the disease which is sickle cell anemia (Shenoy et al., 2016). In fact, relevant studies have revealed that individuals with the sickle cell trait usually do not show any symptoms of sickle cell anemia. What’s more, they have shown hospital admission rates and life expectancies that are similar to the ones of individuals that is not affected by the disease (Stubbs & Suleyman, 2013). Studies reveal that one in five persons in some parts of Africa are a carrier of the sickle cell trait.

This statistic highlights the importance of couples seeking guidance from family planning counselors. Marsha and Clement have sought the advice of a family planning advisor and are therefore better equipped to make informed decisions about their family and sickle cell anemia. They have lost Clement’s father to the ailment as observed above; such could be a cause of anxiety for many other couples that share the same scenario (Stubbs & Suleyman, 2013). The concern can be adequately allayed by seeking counseling services from qualifies health personnel.

A punnet square is a figure or a diagram that can be utilized to make a prediction of an outcome of a cross breed. The square is named after Reginald C. Punnet who came up with the technique. It has been used to predict the probability of offspring possessing a given genotype. The square primarily provides a tabulated summary of the possible paternal alleles with maternal alleles. It is essentially a visual representation of the Mendelian inheritance. In this particular scenario, Marsha and Clement both possess the maternal and paternal alleles; the square can be used to determine the possible outcomes for their babies (Shenoy et al., 2016). Below is a punnet square that will aid in determining the likelihood of Marsha and Clement’s baby having sickle cell disease. The square will further be used to determine the chance that the baby will be a carrier like either of the parents.

Assuming that the gene for sickle hemoglobin is represented by s then;

  S s
S SS Ss
s Ss ss

 

 

From the punnet square, it can be observed that the likelihood of the couple’s baby having a sickle cell is 25%. The figure is gotten because out of the four children; only one will get sickle cell anemia. The condition is recessive; it can therefore only become symptomatic if the baby gets both “s” genes from her parents. The chance of the baby being a carrier like either of her parents is 50%. This is because out of the four children, two would be carriers of the sickle gene but would not be symptomatic (Stubbs & Suleyman, 2013); one will have the abnormal phenotype ss while another will have both normal genes.

If both parents have the sickle cell trait in them (HbAS), there is a one in four chance that any given child will be born with sickle cell anemia. Moreover, there is also an equal one in four chance that one child will be born to the couple completely unaffected by sickle cell anemia or trait. Finally, there is a one in two chance that any given child will be born with the sickle cell trait (Stubbs & Suleyman, 2013). It is important to explain to the couple that the chances remain the same with each pregnancy.

Marsha suggested to the nurse at the local family planning clinic that if the baby were a boy he might have a higher risk of developing the disease, just like his grandfather. If you were this nurse, how would you respond?

As the nurse, I would respond by telling the parents he is no more likely to have the disease because he is male.  He still has a ¼ chance of having the disease.  This is because the disease is not sex-linked or X-linked. If a gene is found to be only on the X chromosome and note on the Y chromosome, then it is termed as a sex-linked gene. In such cases, because the gene controlling the trait found on the sex chromosome the sex linkage is tied to the gender of the individual. This is however not the case for sickle cell anemia. The assumption by Marsha that her baby boy would have a higher risk of getting sickle cell anemia just because of his gender and just as his grandfather had succumbed to is wrong (Anglin, 2015). The belief is a misconception that should be done away with by proper health education and teaching between the caregiver and the families affected by sickle cell anemia.

When Amelia, who does not have sickle cell disease, grows up and marries someone who does have the disease, how likely is it that her children will have the disease? The question does not clearly identify if Amelia is a carrier or is completely free of the sickle cell gene (Yawn et al., 2014). The response will, therefore, analyze the two likely scenarios that could come into play here. If Amelia does not have the disease as stated but is a carrier of the sickle cell gene, there will be zero percent chance of any of their children having sickle cell disease. There will, however, be a 50% chance of any of the given children being carriers of the sickle cell gene but remaining asymptomatic.

The other possible scenario is if Amelia is completely free of the sickle cell disease and is not a carrier of the gene either. In this case the chances that any of her children with her partner will get sickle cell disease are zero percent. Furthermore, the likelihood of any of Amelia’s babies being carriers of the gene is zero. The probabilities will remain the same for each of their pregnancies (Pace, Ofori-Acquah, & Peterson, 2012). The conclusions have been drawn with the assumptions that Amelia’s partner will be completely free of the sickle cell disease and will not be a carrier of the sickle cell gene.

In conclusion, it is important to note that sickle cell anemia is a severe type of hemolytic anemia. The condition comes as a result of develops as a consequence of an individual inheriting a sickle hemoglobin gene. The inherited sickle hemoglobin gene causes the hemoglobin molecule within the person’s circulation to become defective. The sickle hemoglobin then assumes a crystal like formation whenever there is exposure to reduced oxygen tensions. In this paper, however, the focus will be on discussing the genetics around the inheritance of the sickle gene between family members. It is therefore of great importance to teach parents the factors that play in the inheritance of sickle cell disease (Yawn et al., 2014). The paper answered some question on the chances of the Marsh and Clement’s babies either having the disease or being carriers. It has also analyzed the possibility of the couple having children who are unaffected.

The paper has discussed issue of sex linkage for sickle cell disease in depth. The disease is not sex-linked, and therefore Marsha’s fears have been put to rest. The paper has further used a punnet square to identify the chances of getting babies who are carriers, affected, or completely fee of the disease. The punnet square helped reveal that there is a one in four chance of having a baby who has sickle cell disease (Pace, Ofori-Acquah, & Peterson, 2012). The couple also has a one in four chance of getting a baby who is completely unaffected by the sickle cell disease. The couple also has a 50% chance of getting children who are carriers.

The initiative of counseling affected couples and families should be taken up as a health promotion strategy since studies reveal that there are many uninformed people out there who could do with more information on sickle cell anemia. Not only should the affected be educated but all groups should learn about sickle cell anemia. Getting an education and being compassionate plus learning to listen are some key step in overcoming the stigma against sickle cell anemia especially among the youths.

 

 

References

Anglin, C. (2015). Sickle Cell Disease. Journal Of Consumer Health On The Internet19(2), 122-131. http://dx.doi.org/10.1080/15398285.2015.1026706

Pace, B., Ofori-Acquah, S., & Peterson, K. (2012). Sickle Cell Disease: Genetics, Cellular and Molecular Mechanisms, and Therapies. Anemia2012, 1-2. http://dx.doi.org/10.1155/2012/143594

Shenoy, S., Eapen, M., Panepinto, J., Logan, B., Wu, J., & Abraham, A. et al. (2016). A trial of unrelated donor marrow transplantation for children with severe sickle cell disease. Blood128(21), 2561-2567. http://dx.doi.org/10.1182/blood-2016-05-715870

Steinberg, M., Chui, D., Dover, G., Sebastiani, P., & Alsultan, A. (2013). Fetal hemoglobin in sickle cell anemia: a glass half full?. Blood123(4), 481-485. http://dx.doi.org/10.1182/blood-2013-09-528067

Stubbs, M. & Suleyman, N. (2013). Cell biology and genetics (1st ed.).

Yawn, B., Buchanan, G., Afenyi-Annan, A., Ballas, S., Hassell, K., & James, A. et al. (2014). Management of Sickle Cell Disease. JAMA312(10), 1033. http://dx.doi.org/10.1001/jama.2014.10517

 

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