The purpose of this study is to define the natural history of Alexander Disease, a leukodystrophy that causes neurological dysfunction. Investigators will obtain clinical outcome assessments to measure how the disease affects a patient's gross motor, fine motor, speech and language function, swallowing, and quality of life. Specimens are collected to measure glial fibrillary acidic protein (GFAP) levels in cerebrospinal fluid (CSF) and blood. The data obtained from this study will be used for the design of future treatment trials.