Ah, I see. SOMETIMES it is caused by a vitamin deficiency.
But of course, sometimes it is a genetic characteristic which runs in families.
You bring back memories of my attempts to take those darned prenatal vitamins! I was literally unable to deal with them, so I didn't. Four healthy, intelligent, strong-chinned children later, we're all ok! But I still wonder why they can't make those pills SMALLER.......lol