it was touched on above and I do not remember the exact episode of Enterprise...
I do remember that it has something to do with the augments created by Dr. Singh and the Klingons attempting to create their own super-Klingons based on his work.
I remember the original episodes very well and posted the titles from TOS and DS9. I don’t think “Enterprise” touched on the storyline, however. The link I provided gives some additional insight/pov on the issue. Again, fwiw.