For Science!9 Things That Would Actually Happen to a Superhero Exposed to Radiation or MutagenFor Science! - RSS 2.0
3. Gain the power of... Nothing at all!
Sometimes, a mutation has neither a beneficial nor a detrimental effect. The DNA is altered, but there is no appreciable change in the organism. Given the alternatives, this is one of the best fates anyone exposed to a mutagen can hope for. Though I guess lactose tolerance is pretty nice, too.
4. Gain the power of... Uncontrolled cell growth!
The only way the Ninja Turtles are going to grow in size due to exposure to a mutagen is if they develop a bunch of tumors. Cancer is a common result of mutation - common enough that it warrants special mention outside of the other genetic diseases.
You see, a mutagen isn't some sentient being with a design in mind. It's just an agent that causes errors in DNA. Our DNA suffers damage every day, but we have in-built mechanisms to repair this damage. But a mutation in the error-correcting mechanism may lead to DNA accumulating damage more rapidly than normal. Another mutation may cause cells to reproduce more rapidly and frequently. Another may cause a loss of the gene that suppresses tumors. And yet another may cause error signals to be passed on and on and on. The result is the perfect storm for cancerous tumors to spread throughout an organism's body.