10 Grim Realities Of Superhero Origins
9. The Fantastic Four Would Have Alzheimer's

The grim reality: We suppose it probably goes without saying that cosmic rays wouldn't transform you into a fun superhero team. We probably should point out that, despite the name, cosmic rays aren't a fantastical comic book invention, masquerading as science - they're an actual thing. It's something that's actually taken into consideration for space shuttle missions IRL, although for the most part it's just background radiation that doesn't have much effect.
If you were "bombarded" with cosmic rays in the way the Fantastic Four were, then the least you could hope for were cataracts; the worst health effects screw with your central nervous system and accelerate the onset of Alzheimer's disease. Which is a lot less superheroic.