The investigations were based on 3 cases with Leigh, 5 cases with Krabbe's, 4 cases of Alpers, 2 cases with Sandhoff, 1 case with Alexander's disease and 1 case with metachromatic leukodystrophy. In 1 case included into the study we have diagnosed nonketotic hyperglycinemia II. All the diseases under examination are recognized as genetically conditioned or are supposed to be of genetic origin. Damage of the white matter in a more delineated form in certain regions was found in Leigh disease. The changes demonstrated a variable degree of intensity from demyelination to necrosis. More extensive lesions of white matter in gyri and semivoal centrum were found in diseases with simultaneously damaged gray matter e.g. in Alpers and Sandhoff disease. The most extensive changes of diffuse demyelination were found in Krabbe's and Alexander's disease. In these diseases demyelination was accompanied with specific morphological structures e.g. globoidal cells (Krabbe's disease) and Rosenthal fibers (Alexander's disease). The peculiar type of demyelination was characteristic for nonketotic hyperglycinemia of type II. It was expressed by demyelination with vacuolization.