At the next office visit, Dr. Kernodle sat Tazswana’s mother down and gently gave her the bad news:
“Tazswana’s blood tests indicate that she has thalassemia. Roughly, this means that the β-globin protein in her red blood cells is defective, which causes the red blood cells to have an abnormal shape. Her blood cells cannot properly carry oxygen to the body tissues because the abnormal protein cannot bind oxygen. As a consequence, even with treatment, Tazswana will be physically limited. She won’t be able to run and play as other children.”
Devastated that her sweet little daughter might never have enough energy to play “Peek-a-boo” again or run with other children, Mrs. Williams managed to ask:
“How is it treated … is there a cure?”
“Often β-thalassemia patients are treated with frequent transfusions which require frequent hospital visits, but this is not a cure. Additionally, your daughter has a severe form of β-thalassemia and her quality of life would be minimal with such treatment and she would most likely die in her mid-teens. There are two possible cures, one is a bone marrow transplant …”
Mrs. Williams interjected: “She can have my bone marrow!”
“I know you want to help your daughter, Mrs. Williams, but we may be able to fix her own bone marrow stem cells … . There is one possible experimental gene therapy I’d like you to consider, but we will have to test RNA from Tazswana’s blood cells. If Tazswana’s test indicates that she has a certain type of abnormal β-globin, then she may qualify for the experimental study.”
Mrs. William asked: “I don’t know, Doctor, experimental gene therapy … sounds risky. I’ll think about it. How would Tazswana qualify?”
“We can determine whether Tazswana qualifies by looking for this specific change in her RNA.”
“R.N. what?”
“RNA: it’s related to DNA and it can tell us more details about Tazswana’s condition. Altered mRNA is easily detectable using a specific scientific test called a Northern blot—the altered mRNA would be a larger size than normal mRNA.”
“O.K., more information is always good. Can you tell me what the larger RNA size means?”
“Sure I can, Mrs. Williams. This larger size would be due to incorrect splicing of the β-globin pre-mRNA. Rather than having a β-globin mRNA with exons spliced directly together, part of an intron would be retained between the two coding sequences. In other words, part of the β-globin non-coding information would have become part of the code for her β-globin protein. Consequently, the β-globin protein would not be translated correctly and would cause her symptoms. If this is the case, we will need to run a second test (sequencing) to verify that she has the specific intron mutations that the gene therapy is designed to correct. We would look at the sequence of her β-globin pre-mRNA. If this checks out, she would be an excellent candidate for the pre-mRNA gene therapy!”
“O.K., Dr. Kernodle … I don’t completely follow you, but anything that might help my baby girl.”
Examine Handouts 6–8 and discuss and answer the questions listed on each of the handouts.
Originally published at http://www.sciencecases.org/tazswana/tazswana5.asp
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