After skimming through, one obvious question follows: How can they ensure that (only) one out of three chromosomes only, have XIST integrated? (I assume they c

After skimming through, one obvious question follows: How can they ensure that (only) one out of three chromosomes only, have XIST integrated? (I assume they can target these three chromosomes due to the CRISPR RNA.) So down syndrome is trisomy 21, aka three chromosomes 21. Say you have to modify a billion cells, just to give a number. Well, how can you ensure that all those have one XIST gene that is also active (otherwise it would be pointless; XIST produces a RNA which in turn silences the X chromosome by coating it)? Inserting new genes is nothing new, that is already ancient technology at this point in time. https://en.wikipedia.org/wiki/XIST https://en.wikipedia.org/wiki/XIST