Neuronal ceroid lipofuscinosis 10 (NCL10) is a lysosomal storage disease affecting dogs. NCL10 is due to a deficiency in the activity of the Enzyme cathepsin D, 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 typically present between 1 to 3 years of age with progressive neurologic disease. Symptoms include a lack of muscle coordination, abnormal gait and difficulty balancing. Disease progression is slow, but dogs are generally euthanized within 2 years of diagnosis when they can no longer stand or walk on their own.