GFAP and leukoencephalopathy, megalencephalic: Our initial focus on white matter responses relates to the fact that GFAP was first purified from an MS plaque [66] with astrocytes being widely observed in demyelinating conditions [67], including MS [68, 69], Alexander Disease [70], Megalencephalic leukoencephalopathy with subcortical cysts [71], and vanishing white matter disease [72].