Fucosidosis is an inherited lysosomal storage disease affecting English springer spaniels. Affected dogs have a deficiency of the Enzyme alpha-L-fucosidase which is responsible for breaking down complex sugars during normal cellular metabolism. As a result, there is an accumulation of these compounds primarily in cells of the nervous system affecting the normal function of the brain and nervous system. Affected dogs typically present with symptoms between 11 months and 4 years of age. Symptoms include loss of balance, deafness, change in temperament, loss of learned skills, blindness, difficulty eating, and weight loss. Once an affected dog begins to show signs of the disease, dogs are usually euthanized within 18 months.