My brother has hair growing from his fingernails. is that normal? what could be causing that.

NOT normal; unknown: Not only is this NOT normal (did you really think it was normal? how many people have you seen with this?), but I've never heard of this. I did some research and have not found a single report of this happening ever to anyone. Thus I have no idea what could be causing it, though I wonder if your brother might be an alien. He might want to consult a dermatologist, or Ripley's Believe It Or Not...