How do you be born a werewolf?

At the moment it's impossible without genetic modification and even with it, it would be a long and painful transformation. Our bones just don't change that fast mate.

There is no scientific evidence that werewolves even exist, on this planet anyway.
There are 2 different ways I can answer that.

First way: You have to be bitten by a werewolf to actually become one.

Second Way: There is an old spell that people used to put on their enemies to turn them into werewolves.