Help with magic system based chronic illness

I created a blood/DNA magic system where you have to be born with magic for it to work, but while revisiting the worldbuilding, I recently had the idea to add a way to get magic if you weren't born with it. For context, the magic system is an invading organism that hijacks your bone marrow into making copies of it, kinda like cancer. Groups of humans started to evolve past the disease by pushing them out the body and that's basically how the magic works. My idea is that people can grow their magic count and speed up the evolution process. I haven't fully worked out the details on this yet, but I do know that I want to give the people who weren't born with magic a much higher chance of a magic related chronic illness. The chronic illness happens because someone doesn't push out enough of the magic for too long of a time period, and because it's harder for the people who weren't born with magic to push enough of the magic out, they have a higher chance of the chronic illness. People who were born with magic also get the illness too. I'm worried this comes off as you have to be born great to be great, which is the whole reason I'm adding a way to get magic without being born with it.