Neuronal ceroid lipofuscinosis 2 (NCL2) is an early-onset, lysosomal storage disease affecting dogs. NCL2 is due to a deficiency in the enzyme tripeptidyl peptidase (TPP1), which is necessary to break down certain proteins in the cells. As a result, there is an accumulation of these compounds in cells, which affects the normal function of the brain and nervous system. Affected dogs present with progressive neurologic disease around 9 months of age. Symptoms include loss of learned behavior, mental dullness, ataxia, loss of vision, weakness, abnormal gait, seizures, tremors and aggressive behavior. Symptoms progress very quickly and dogs typically die by 12 months of age.