A disease in monkeys have been found that mimics a neurodegenerative disorder in people; specifically children. A population of Japanese monkeys were found to carry a mutation in the CLN7 gene and the disease is called Batten disease. It affects the nervous system by affecting lysosomes in cells. The function of lysosomes are to break down waste, but when the gene is mutated, lysosome produces a broken form of the protein which results in the buildup of "junk." This disease starts during childhood with symptoms such as vision loss, seizures, and eventually, the loss of cognitive functions. With the discovery of Batten disease in monkeys (which are closely related to humans), Oregon Health and Science University can perform gene therapy and discover ways to cure the disease or slow it down.
I personally think that this is the start to finding a cure for the Batten disease and any other diseases. When we discover that another animal has the same type of disease humans do, we can use this information to develop solutions.