GM1 gangliosidosis (Portuguese water dog type) is an inherited Lysosomal Storage Disorder affecting dogs. Affected dogs typically present with symptoms of neurologic disease around 2 to 6 months of age. Dogs with GM1 gangliosidosis have insufficient activity of the Enzyme beta-galactosidase, which is responsible for breaking down specific carbohydrates in the cells. As a result, there is an accumulation of break down products such as GM1 in cells, especially cells of the brain and nervous system. Symptoms include vision loss, Nystagmus, difficulties walking, loss of balance, head tremors, abnormal bone growth and weight loss. Once an affected dog begins to show signs of the disease, the disease progression is rapid and dogs usually die by one year of age.