If it was "passed by Mom" then they're probably talking about demodectic mange. Demodectic mites are indeed passed from mother to infants in the first days of life. What people don't seem to realise though is that that's to every
infant. All dogs have demodectic mites, all of the time. They're a natural flora of the coat and live inside the hair follicules in harmony with their host. You have them too, btw, albeit a slightly different species.
Mange only occurs when the dog has an immune system deficiency which allows the mites to multiply out of control, causing damage to the hair follicules, and hence hair loss. It is not normally a life-long problem. Demodex is often called puppy mange - for the reason that the vast
majority of animals affected are puppies. And they don't have defective immune systems, they simply have as-yet undeveloped immune systems (immunity to disease isn't something you're born with, it's something that develops over time - and why children are more vulnerable than adults). Once that immune system develops, the individual will recover from the mange all on their own with no intervention at all, thanks very much
That applies to over 90% of cases (so for 90% of dogs, demodex is NOT a lifelong issue).
Your dog, however, is one of the 10% of cases for whom it is likely
to be a lifelong issue. And that's because he developed generalised mange. That indicates an actual problem with the immune system, not just an animal whose immune system wasn't fully developed at the time. Now that can occur in cases of extreme hardship, of course. A dog half starved to death, for example, is going to be very vulnerable to disease - and when properly fed and cared for will rebound. But in most cases, you're talking about a defective immune system - which means he'll be vulnerable all his life (and not only to the development of mange).
It's worth noting that defective immune systems are hereditary, so any dog that either develops generalised mange or is treated for localised mange must never be used for breeding. His parents and siblings should not be bred again either (not that any of that is likely to be within your control - but it's a fact worth noting should you ever run across some idiot who wants to breed a dog with a defective immune system).