I'd say in Billy's case, it's a symptom, not a diagnosis. And it may or may not be true depression. I'm probably going to hit a raw nerve with someone, but honestly.......I think we "over do" depression. If one is sad, we tend to take it to the extreme and they're depressed. If one is bored with their life (and c'mon, we all know we go through such stages), they're depressed. If something isn't working out as planned and the person is bummed about it, they're depressed. I'm sorry, but most of this is just normal down in the crapper stuff, not true depression. So I get a bit irked when the term gets over used.
Travis has his psychiatric evaluation for SS coming up soon. I can't wait to hear all the dxes spew forth. And I'm sure they will because I've told him to be utterly honest, be himself......don't try to impress or whatever.
Travis is Pervasive Developmental Disorder (PDD) and on the lower end of the autistic spectrum. When SS asked what a typical day for him is like it was more or less one sentence. He gets up, sits at his computer desk, works on the same computer game he's been working on for years, maybe will watch a movie or read on the computer. During this he might wander downstairs to grab something to eat or to sit down at a meal I've cooked. His only social interactions are with immediate family (and even that is minimal compared to what society views as normal ) and the one to two people he works on the game with if they happen to be online. Then he gets up to go to bed. He doesn't do anything with his clothing (not even change it), hair, doesn't bathe......unless told to do so by me because either I've seen the same clothes for too many days or I get a whiff and want to fall over.
This alone has been classified as "depressed" since the first time he walked into a psychiatrist's office. (which is why I stopped taking him) I assure you, he's not depressed. This is his "normal" state. No, he's probably not thrilled to death either. But Travis as an adult no longer goes to extreme as often in emotion. As a child, oh heck yeah, we had a heck of a time with it swinging back and forth because every emotion he had was felt 100 X's that of a "normal" person. If pushed.......as in anger, I have still seen situations when it can be triggered. But otherwise, no. Travis adored mother in law and they had a special bond, he'd do anything in the world for her. When she passed, he was sad but someone who didn't know him well would say he didn't even grieve her passing. Same with his dad. I know both losses hurt him........it just isn't felt the same way we feel things, it goes along with the "out of sight/out of mind" thing that many on the spectrum seem to have going on, which those in this family definitely had as a strong trait. He felt the hurt, it was done, he let it go and life goes on. Know what I mean??
This also goes hand in hand with pleasure. I saw it with husband.....I see it with Travis. And yes, I think they both realized that they didn't "feel" it like other people usually do. But I don't find that surprising either. Now I can't speak for those higher functioning than Travis......but say you were to give him a gift, if that gift isn't within one of his obsessions, you've wasted your money if you think he's going to be thrilled to death. That doesn't mean he doesn't like the gift or that he won't enjoy it to some degree, you just aren't going to see any real reaction from him about it. Travis does say Thank you because he was taught to do so no matter if it was the worst gift in the world, had he not been taught to do so, he probably wouldn't even think to thank for a gift outside of his obsession thing.
I'll tell you want, I know I'd be bored out of my ever loving mind if I were to "create" the same darn video game over a period of several years. Travis finds pleasure in it though, obviously quite a bit or it wouldn't have lasted so long. I know he's "excited" about it when he comes and tells me something they're working on.........and no, this is not you're typical "excited" behavior, but then again it is for him.
But Travis' reclusive behavior, little to no desire for social interaction, lack of personal hygiene, and repetitive behaviors usually gets him diagnosed severely depressed with Obsessive Compulsive Disorder (OCD), when that is not even remotely close. It is the autism with some Traumatic Brain Injury (TBI) thrown in to make it interesting and to me any psychiatrist or therapist too stupid to figure that out doesn't need to "treat" my kid.
Sorry. I think I might have went off on a tangent. But with you believing strongly that Billy is on the spectrum, you have to keep in mind that his thought processes are simply NOT like everyone elses. What we perceive as normal doesn't really apply to them because their "normal" is so vastly different from ours depending on where they're at on the spectrum. I'm not saying he can't be depressed, because that's not the case. I'm saying you & a psychiatrist would have to carefully look at his daily life and talk to him to find out if anything really has changed to indicate he is depressed or has issues feeling pleasure.
I say this because I can't tell you how many times Travis has come to me with one psychiatric diagnosis or another scared to death he has it because of the symptoms they list. And each time we go over them and I explain that those are symptoms of the autism or Traumatic Brain Injury (TBI) or whatever and he feels huge relief. (I'll also ask questions to make certain other things in his daily life haven't' changed as well) Honestly, from what I've gathered over the years, those on the spectrum can grasp eventually that there is a huge difference between them and the rest of the world. What they seem to never stop struggling with is why that is the case.
So......... I dunno if that helped you or not. I do know I saw the same things with husband's bro (who just has strong traits) and his cousin (who is fairly high functioning). So it's not just husband and Travis.