I doubt there are mutants out there very much. I could probably believe that there are some humans who have some terrible diseases e.g. the Elephant man - for some reason I can imagine that being real as the human reaction towards him
As much as I would fancy the idea of a government secrety creating super mutants e.g. diclonius in Elfen Lied or X-men or psychics [Akira anyone?] it seems a bit out of reach and if any had any kind of threat they would be wiped out pronto. But who knows maybe some country in this world who are planning to take over the world may have some horrific mutant breeding facility on some remote uninhabitied island