The neuronal ceroid lipofuscinoses (NCLs) are a group of inherited lysosomal storage disorders. Affected dogs lack a specific Enzyme necessary for normal metabolism. As a result, there is an abnormal accumulation of waste compounds primarily in the cells of the nervous system, leading to a range of nervous system disorders. Dogs affected with NCL (Tibetan terrier type) present with progressive loss of vision and behavior changes beginning around 4 to 7 years of age. Symptoms include a lack of muscle coordination, abnormal gait and difficulty in balancing and jumping. Affected dogs may also display aimless wandering behavior with episodes of confusion, depression, aggression, seizures and frequent barking. These symptoms become more frequent and severe over time. As the disease progresses, dogs may lose sensory skills and vision. Signs of Dementia may include loss of learned behavior, irritability and aggression. There is currently no treatment for the disease.