Humans exposed to nicotine, smokers, and patients receiving nicotine treatments (patients with Alzheimer's disease, Parkinson's disease, or ulcerative colitis) may have altered CYP2E1 levels and activity, mediated metabolism of drugs and toxins, and altered toxicity generated by the CYP2E1 metabolism [44]. The gene discussed is CYP2E1; the disease is Alzheimer disease.