Forcing RNA to, at least, Mumble…

BY MARK MCQUAIN

We are at a turning point in medicine where instead of supplementing patients with proteins or enzymes that their bodies fail to manufacture due to genetic abnormalities, we soon may be able to re-engineer the abnormal DNA, restoring the DNA’s ability to instruct the body to make those same proteins or enzymes. On our way to full-fledged genetic engineering, we have learned that DNA makes something called RNA, which can be thought of as specific instructions for assembling these vital proteins, telling cells exactly how to assemble protein building blocks, called amino acids, in their proper sequence. Even a very minor disorder in a very long amino acid sequence of a protein can cause that protein to function poorly or not at all. When bad DNA makes bad RNA, or when good RNA gets subsequently damaged or misread, the protein either gets assembled in a garbled fashion, or not at all. Think of RNA as the boss of protein production who can speak clearly, mumble or say nothing at all. Recently, there is one well-known disease where it looks like it is possible to force bad RNA that presently says nothing at all to, at least, mumble.

The disease is Muscular Dystophy (MD) and the missing necessary protein is called dystrophin. Dystrophin is responsible for the structural integrity of muscle. Poorly formed or garbled dystrophin results in a mild form of MD, such as one called Becker Muscular Dystrophy (BMD) where patients can live well into their 40s or 50s. If no dystrophin is produced at all, a severe form of the disease called Duchenne MD (DMD) results, in which muscles simply fall apart over a shorter period of time, causing patients to stop walking in their teens, usually dying in their twenties from cardiac or respiratory muscle failure. While it would be great to restore normal production of dystrophin in patients with DMD, one company called Sarepta, appears to be able to cause patients with DMD, who normally do not make any dystrophin, to produce a garbled dystrophin, giving them a milder BMD-like disease.

Consider the following sentence: “The big red fat cat bit the sly fox and ate the shy jay”. The individual letters represent the RNA sequence and the three letter words represent unique amino acid protein building blocks, resulting in a meaningful protein sentence – think of this as the normal dystrophin protein in a healthy person. If the RNA was missing the 22nd through 24th letters (the 8th word “sly”), the sentence becomes: “The big red fat cat bit the fox and ate the shy jay”. It is a minimally garbled version of the first sentence but still meaningful – think of this as the dysfunctional dystrophin in milder BMD. If the original RNA sequence was missing only the 7th and 8th letters, the sentence becomes: “The big dfa tca tbi tth esl yfo xan dat eth esh yja y”. This sentence has no meaning beyond “The big” – think of this as no dystrophin in severe DMD. If we could get the RNA reader to ignore the first letter “d” in the last RNA sequence, the sentence becomes: “The big fat cat bit the sly fox and ate the shy jay”. We are back to a minimally garbled version of the first sentence but still meaningful – think of this as another dysfunctional protein in a milder “Becker-like” MD. This is how scientists at Sarepta appear to have taken an RNA sequence that originally said nothing and forced it to mumble, producing a new garbled form of dystrophin, which works better than no dystrophin at all.

I realize this has been a long walk in the weeds for some of our regular readers but hopefully it has provided some helpful background into the current treatment of MD and a sense of how much further we have yet to go. I will use this blog entry as background for my next blog entry to discuss some of the bioethics around the cost of getting RNA to mumble.

For now and for me, advancing medical knowledge like this convinces me of how fearfully and wonderfully we are made. (Psalm 139:14)

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