This mutation grants:
+5 to max HP +95 resistance to all anti-aging methods(currently just rejuvex).
note: this mutation does not affect endocrines at all, whether it is chance of endocrines working, or the max HP gained from endos. You could still, theoretically, take this mutation as your first, and use endocrines to boost your HP all the way up to 60, and it would be no more difficult than taking them up to 55 without the mutation.
The fibrocartilage mutation gives you +5 to your max HP. On top of using endocrine boosters to reach 55, the additional bonus from fibrocartilage means you can reach 60 max HP.
+95 resistance to all anti-aging methods. This means, if you have a habit of dying a lot, or removing mutations, you are going to be quite old, and you will have to use a lot of rejuvex to get down to a younger age to avoid heart attacks and such.