Sickle cell anemia or sickle cell disease is a form of anemia that depending on the genotype causes severe or mild symptoms. If you are a carrier of the disease you only have one allele and that doesn’t affect you much. Unless you climb to a very high mountain you probably won’t have any problems. You will however have to consider if your partner is also a carrier. In that case you have a 25% chance of having a child with the severe form of the disease. This can result in frequent pain crises, silent cerebral infarct, stroke, end organ damage and early death.
This is caused by a single mutation of one base in the sixth codon of β-globin part of the adult haemoglobin. The problem with this haemoglobin is that it isn’t as good as normal haemoglobin at carrying oxygen from the lung to the tissues. As result the red blood cells containing this dysfunctional haemoglobin take a sickle like shape like a half moon.
There are different solutions for this mainly for limiting symptoms like blood transfusions, preventive therapies including penicillin prophylaxis and pneumococcal vaccination, and hydroxyurea therapy. Those are not permanent though. An alternative would be gene therapy. Gene therapy is still experimental and we are unsure about the side effects it may cause. But all the trials and studies are positive and even in theory it should be fine.
For sickle cell anemia there are ways to use gene editing tools like CRISPR to modify the affected nucleotide and basically modify the haematopoietic stem cells to produce normal haemoglobin. Clinical trials in which the normal gene has been added alongside the dysfunctional one, show promising results although those utilizing more modern techniques like CRISPR may show even better long term permanent results.
The side effects with the more recent vectors and methods used are limited which is good, although older methods have some small issues. Still those are not significant in my opinion compared to those caused by the disease itself.
I think it is great that we see progress in such diseases that in terms of genetics seem easy to fix. It is caused by a single nucleotide, this makes it easier to fix compared to diseases that are caused by mutated chromosomes or multiple genes on different chromosomes. So if we make the first steps on developing an effective gene therapy for diseases like sickle cell anemia we will end up being more prepared to develop gene therapies for more complex diseases.
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