Not sure what you're referring to but it's not 1 percent.. it's not even 0.01 percent.
Cursory search: https://www.webmd.com/parenting/baby/news/20190503/study-abo...
Cursory search: https://www.webmd.com/parenting/baby/news/20190503/study-abo...
Many, many more people have different genetic configurations that can manifest well after birth.
I'll admit I rounded up to one percent from something that was a large fractional percent.
Assuming good intentions based on your other comments, but these things can elicit negative responses.
My intuition, reading through the studies and talking a conservative estimate, is that something like 0.6 to 0.8% is a defensible estimate. I rounded that to 1%. Other scholars pick higher or lower numbers, but it's not 10%, and I firmly believe that it's not 0.1% based on studies, which makes 1% the correct order of magnitude, imo.