 Transplantation with allogenic hematopoietic stem cells has been shown to positively influence the disease progression of other lysosomal storage diseases such as Hurler Syndrome and Krabbe Disease and testing for enzyme replacement for MLD is already underway. For future researchers to be able compare the benefits of children with MLD who receive treatment to those who remained untreated, a better understanding of the natural progression of late infantile MLD is necessary. The current literature contains studies of individual or small groups of MLD patients that tracked intelligence quotients and neurophysiologic function, but did not correlate this with patients neurodevelopment. A longitudinal study of a larger population of patients with late infantile MLD has yet to be performed. This protocol is a longitudinal observational study to capture natural history data in patients with late infantile MLD. This data will provide baseline neurobehavioral, neuroimaging, and neurophysiological information that can in the future be used to evaluate treatment effects. 