How adjectives is it to be born lacking a thumb muscle?

I went to the Science Center today next to the boy i'm seeing and we were comparing our dominant and recessive traits at one exhibit, when I held up my thumb to see if it be a hitch-hikers. He shows me his, and says he can't bend it put money on at all because he be born with out the muscle, and that most kids who are born that process have to own their thumbs amputated. I thought this was strange. It is alil strange, i enjoy never even heard of mortal born without and kinda missing muscles...and i own been studying the human body for going on 3 years...ever since i started elevated school...
hmmmmm strange possibly hes a alien. jk. yeah it is common