Rheumatoid arthritis is an autoimmune disorder in which antibodies are produced against the synovial membrane and cartilage. Vitiligo causes white patches on skin and is also characterised as an autoimmune disorder. Psoriasis is a skin disease that causes itchy or sore patches of thick red skin and is also autoimmune, whereas Alzheimer's disease is due to deficiency of the neurotransmitter acetylcholine.