<prompt> Dementia, dermatitis, diarrhoea are features ofBed BedPellagraVitamin B12 deficiencyPyridoxine deficiency  <response>: Deficiency of niacin causes pellagra, a disease involving the skin, gastrointestinal tract, and CNS. The symptoms of pellagra progress through the three Ds: dermatitis photosensitive, diarrhea, and dementia. If untreated, death a fourth D occurs. Hartnup disorder, characterized by defective absorption of tryptophan, can result in pellagra-like symptoms.Ref : Lippincotts illustrated reviews for biochemistry , 7th edition. 