Late infantile ceroid lipofuscinosis (LINCL) is a rare, rapidly progressing lysosomal storage disease resulting from mutations in the CLN2 gene that lead to deficiency in the lysosomal protease tripeptidyl peptidase I (TPP-I). The symptoms are largely neurological with onset at 2-4 years age with progression to death at age 8-12 yrs. The rareness of the disease and the likelihood of non-uniform progression depending on genotype together limit the data available regarding the natural history of disease progression. Current neurological rating scales are used to give an overall quantitative description of the disease but the categories are generally broad and imprecise. With that background, the primary focus of this study is to use clinical rating scales and magnetic resonance imaging methods to define the natural history of LINCL and to provide objective and sensitive surrogates for neurological status and the impact of experimental treatments in children... (for more see dbGaP study page.)