What symptoms a vitamin B12 deficiency can cause?

Links: 1) http://en.Wikipedia.Org/wiki/vitamin_b12_deficiency 2) http://www.Doctoroz.Com/videos/end-your-energy-crisis-vitamin-b12 3) http://chriskresser.Com/b12-deficiency-a-silent-epidemic-with-serious-consequences 3) http://www.Webmd.Com/food-recipes/guide/vitamin-b12-deficiency-symptoms-causes.