Apart from monkeys or the ape family, in what other species has Down's syndrome been detected?

According to New Scientist, in 1989 RESEARCHERS in Wisconsin have reported the first known case of a monkey with Down-like syndrome.

Does anyone know if Down’s syndrome has been discovered in other species apart from the primate family?

Does anyone have any other hypothesis/guesses (apart from mother’s age and extra copy of Chromosome 21) on the cause of Down’s Syndrome?

I will welcome all opinion no matter how far-fetched.