Clinical aspects and pathology of Alexander disease, and morphological and functional alteration of astrocytes induced by GFAP mutation.
Alexander disease (AxD) is pathologically characterized by the presence of Rosenthal fibers (RF), which are made up of GFAP, αB-crystallin and heat shock protein 27, in the cytoplasm of perivascular and subpial astrocyte endfeet. Since GFAP mutation has been confirmed in reported cases of AxD, clinical or experimental research is being conducted on the relationship between GFAP mutation and the onset pathology as well as the clinical form. We conducted a nationwide survey and a clinical study, and classified AxD into three types: cerebral AxD (type 1), which primarily has an infantile onset with presence of seizures, psychomotor developmental retardation, macrocephaly, and abnormalities in the superior frontal cerebral white matter observed in a brain MRI; bulbospinal AxD (type 2), which primarily has an adult onset with presence of muscle weakness, hyperreflexia, bulbar or pseudobulbar symptoms, signal abnormalities, and atrophy observed in an MRI of the medulla oblongata and upper cervical spinal cord; and an intermediate form (type 3) which has the characteristics of both. A research on GFAP mutations and aggregate formation concluded that GFAP mutations decreased the solubility of GFAP. According to our cell model experiment, the formation of mutant GFAP aggravates depending on the site of the GFAP mutation. Furthermore, there is a possibility that polymorphism in the GFAP promoter gene regulates the degree to which GFAP is expressed; it may have an effect on clinical heterogeneity. Recent research using cell and animal models suggests that the pathology of AxD involves not only mere functional abnormalities in intermediate filaments but also functional abnormalities in astrocytes as well as in neurons. Clarification of the glia-neuron interactions will prove the disease to be very interesting.