HLA-DR (Class II MCH antigen) exhibit significant differences between ADHD and Parkinson's disease, stroke, vascular dementia, AD, and vascular encephalopathy; between epilepsy and Parkinson's disease, stroke, vascular dementia, AD, and vascular encephalopathy; and between mental retardation and Parkinson's disease, stroke, vascular dementia, AD, and vascular encephalopathy. Here, PMCH is linked to Alzheimer disease.