Jamie was born with a type of intersex condition, meaning he had characteristics that was somewhere between male and female. So he wasn't necessarily just a boy or just a girl. But his aunt decided to go ahead and list his gender as male, to try to make everything a little easier so Jamie wouldn't grow up wondering which gender he was. And when he got older he would decide if he still idenitified as a boy or not.
As for the "mutant" thing, that's just something Jamie refered to himself as. His body is different from "normal" people (the stuff I mentioned above) and it's just how he felt.
Jamie was born with a type of intersex condition, meaning he had characteristics that was somewhere between male and female. So he wasn't necessarily just a boy or just a girl. But his aunt decided to go ahead and list his gender as male, to try to make everything a little easier so Jamie wouldn't grow up wondering which gender he was. And when he got older he would decide if he still idenitified as a boy or not.
As for the "mutant" thing, that's just something Jamie refered to himself as. His body is different from "normal" people (the stuff I mentioned above) and it's just how he felt.
I hoped I answered your questions clearly!