Both hereditary diffuse leukoencephalopathy with axonal spheroids (HDLS) and cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) are autosomal dominant white matter diseases. First symptoms of HDLS are cognitive decline or dementia, while those of CADASIL are migraine or ischemic infarcts. Family histories of young patients with stroke are important, because most of patients with CADASIL have these family histories. Temporal pole lesions are specific for CADASIL. However, some of the patients have no such lesions. We should differ CADASIL from non-CADASIL by evaluation of family history or the other MRI findings such as confluent external capsular lesions or multiple white matter medullary infarcts. Coronal views of MRI are useful for differentiating ischemic lesions from demyelinated lesions, even if horizontal views of MRI give little information. In addition, evaluation of immunohistochemical staining of Notch3 by frozen skin samples is useful for diagnosis. We discovered the methods of detecting light microscopic findings of GOM in frozen section. To reveal the pathogenesis of CADASIL, it is indispensable to analyze the chemical nature of GOM by histochemical stainings. We are going to analyze coexist proteins or materials in small arterial granular degeneration by proteomics of LC/ MS/ MS.