Here is a link for a
free DNA test for Degenerative Myelopathy. If your pug has been diagnosed by your vet with DM, you can send a sample in for a free DNA test to confirm. this. It is also a great help to them to get these tests from the different breeds that are not usually diagnosed with DM. You would be helping their research project, and at the same time confirming the diagnosis with no cost.
http://www.caninegeneticdiseases.net/DM/resrchDM.htm There are lots of good articles on IVDD, and I think your pugs are probably one of these two diseases. Sorry did not mean to denegrate your vet, but there is no research or any info on hereditary spinal degeneration that I can find. I have consulted some extremely knowledgable pug people this am, and they have not heard of it either. So I am assuming your vet meant one of these 2 things.
Hope it all works out for you and your pugs, whatever the cause, carts will be good for them,,,,,,,,,,,,,and for you. I find it a lot easier to express bladders and bowels whilst they are standing in their carts.
Hugs Joan