I wouldn't rush to discard the hypothesis entirely...

I wouldn't rush to discard the hypothesis entirely but it would sound better if they had implicated this casein variant in fewer conditions!
Among them, type 1 diabetes. Reminds me of 1993-94 when I was working on it. Nobody was talking about casein but another cow milk protein, bovine serum albumin (BSA), was suspected to trigger the immune system to destroy the insulin-producing cells. Besides BSA, there were many other suspects - some viruses, some host proteins, some genes controlling the immune response.
More than a decade later, the situation in type 1 diabetes research hasn't changed much. Some of the suspects remain, some have been all but cleared, including BSA - but casein seems to have taken its place. Still nobody knows the precise cause(s) of diabetes, a prevention method, a treatment other than good old insulin or a cure other than pancreas transplant(which sounds scary when I switch to think about autism, because what exactly could be transplanted to cure autism)?
When not ready to solve a problem, science just circles around it.