There is no mRNA gene therapy that is FDA approved. There is a mRNA gene therapy for rabies that is nearing the end of animal testing, entering phase 1 of human tests. So far the mice have survived, and they still haven't finished with pigs and other analogs, but the models say that the mice result should be the same. Essentially mRNA gene therapy "vaccines" have the potential to work on a whole bunch of diseases which have been difficult to treat with standard vaccines, but there is no track record for any. The most common side effect is swelling, which can lead to death. Records of cytokine storm from infection after taking the shot is mostly being suppressed, so it's all a guessing game.