Tauopathy is an integral phenotype of AD, as well as several related disorders including frontotemporal dementia, Pick's disease, Huntington's disease, progressive supranuclear palsy, corticobasal degeneration, argyrophilic grain disease, tangle-only dementia, white matter tauopathy with globular glial inclusions and Down's syndrome.39, 40, 41, 42 Recent studies showed that reduced BDNF expression and BDNF polymorphisms also existed in other diseases with tauopathies. The gene discussed is BDNF; the disease is Huntington disease.