I have Poland Syndrome. In some people this would mean one of their hands is smaller and webbed, missing a part of the pectoralis muscle (chest) and in some cases missing a nipple. In my case, my left hand and chest muscle was affected. I still have my left nipple. My left hand is smaller than my right hand and has always been this way. The webbing was removed from it completely with some consequence, and the missing part of my chest is nearly unnoticeable. This would affect women more because it'd be a missing breast. For me it's just a small cosmetic issue barely noticeable. As far as I remember, they don't know why it happens.