There's a girl with an extra toe in there too. The telepath thing is just one possible mutation, from what I recall. In the more irradiated parts the mutations get more extreme.

Having 6 toes is as common as webbed feet in today's world, and its not all that uncommon (I was born with 6 toes, my dad had 6 toes and fingers). They don't have bones and surgeons just cut them off at birth these days.

In my mind the more fantastical mutations in the book make it a bit more far fetched and give it that sci-fi feel.