Wetting

My older brother is 32. He has autism. He has recently started wetting himself. Twice he has wet the bed and three times in public. He is quite capable and mum says he has never done this since the day he was potty trained. She's despairing as she doesn't know why he is doing it and he won't talk about it as he gets embarrassed. She is assuming it's to do with his Autism, worrying he is depressed or something. I've suggested it could be a medical reason, he tends to not tell us when he is in pain or uncomfortable. Anyone had any experience of this? Why would this begin now when he has never done this before? How do we make this better?