Gene Therapy and X-Linked SCID

In class this week, we learned about various patterns of inheritance. These included simple Mendelian inhertiance, incomplete dominance, codominace, sex-influenced inheritance, and X-linked inheritance. For this blog post, I am focusing on the last of these types of inheritance patterns.

X-linked severe combined immunodeficiency, or SCID, is a disease that causes people to not have functioning immune systems, leaving them susceptible to life-threatening infections. This disease results from a lack of T cells and natural killer cells as well as nonfunctional B lymhocytes (remember these from A&P?). Children with this disease are usually diagnosed to the recurrence of infections despite normal treatment. The final diagnosis of X-SCID is done by checking lymphocyte counts, lymphocyte functionality tests, and testing of the molecular genes. The best treatment for SCID is a bone marrow transplant from a genetically matched sibling. In the absence of such a sibling, unmatched donors are often recruited to donate bone marrow although these transplants are only about 70 percent successful.

As seen in the name of the disease, the inheritance of this condition is X-linked. This condition is more likely to occur in males, since they only have one X chromosome. Therefore, there is no recessive or dominant involved in their inheritance. In a female, it is possible to have recessive X-linked conditions that are not expressed due to the presence of normal genes on the other X chromosome. This is not an option for males, since they have an X chromosome and a Y chromosome. If a mother is a carrier for this disease, the chance of her transmitting this gene is 50%. Males who have SCID can only pass this gene on to their daughters, and not their sons. As we know from what we learned in class, this is because an X chromosome is contributed to daughters while a Y chromosome is contributed to sons. It is possibly for prenatal testing to be conducted on women to determine if they are carriers for this disease.

Feel free to read this article, from which I retrieved my information, to understand more about this disease. I mainly attempted to focus on the information that was relevant to our current chapter of patterns of inheritance.