Vitamin B-12 deficiency.  Common, with troubling symptoms.
D006801:Humans; D014805:Vitamin B 12 / Q000008:administration & dosage / Q000502:physiology; D014806:Vitamin B 12 Deficiency / Q000209:etiology / Q000378:metabolism / Q000517:prevention & control; D014803:Vitamin B Complex / Q000008:administration & dosage
D014803:Vitamin B Complex; D014805:Vitamin B 12