Yes, gestational diabetes is also another factor that increases the risk of schizophrenia in off-spring.

"Epidemiologic studies have shown that the offspring of mothers who experienced diabetes mellitus during their pregnancies are 7 times more likely to develop schizophrenia, compared with those who were not exposed to diabetic pregnancy."[1]

Infections also contribute too...

"maternal influenza A in pregnancy has been suspected to have a connection with schizophrenia in the offspring. Brown et al. found that influenza exposure, especially during the first trimester, might increase the risk of schizophrenia (odds ratio 7.0; 95% confidence interval 0.7–75.3). Prenatal exposure to rubella has also been connected to non-affective psychosis"[2]

I'm sorry to say, but considering everything you've stated it's effectively a definitive diagnoses. He has schizophrenia or schizoaffective disorder; I'd probably shelve, or entirely abandon, the ADHD diagnoses. The final decision between schizophrenia and schizoaffective disorder will largely come down to how severe his mood problems are. Does he have clear cut examples of mania or depression that last for weeks? The mood symptoms need to be more than just day to day emotional reactivity to satisfy the criteria for schizoaffective disorder.

From a practical perspective, I would just establish his diagnoses as schizophrenia. It's easy for others to understand schizophrenia, for instance, educators have been train to deal with it. You will also have to fight less with insurance and social security disability, as for some reason providers are more willing to recognize schizophrenia as a neurological disorder.

He may always have school problems, you will need to go to his school and talk to someone about setting up an individualized education program.

He may not ever be able to support himself entirely on his own, this is the reality of the situation. When he gets older I would retain an attorney to get him on social security disability as soon as possible, this will take the pressure off you and him so he can focus on things like working at his own pace to complete a college degree. Social security supplemental income isn't much, but it will at least be enough that you can get him his own apartment. Developmentally, he'll likely be at least five years behind the curve. Once his diagnosis is confirmed by your psychiatrist he will likely qualify for some form of public medical assistance, visit your local medicaid office. http://www.medicaid.gov

It will be helpful to get a dedicated social-worker that you can see often. They're very useful in helping to work through the day to day problems or getting you the resources you'll need. Later in life, they'll be able to help your child develop the skills they need to live on their own.

Hopefully, with the recent medical advances it won't be as hard as I described. I wish you and him the best of luck. If you have any more questions let me know. Do not entrust your boys health to a general psychiatrist, you need a, childhood, schizophrenia specialist. You should be able to find such a specialist at a university teaching hospital. The quality of care he receives now will impact him for the rest of his life. You will need to be his advocate, always remember the squeaky wheel gets the grease.

[1:Diabetes mellitus during pregnancy and increased risk of schizophrenia in offspring: a review of the evidence and putative mechanisms
[2]:Predictors of schizophrenia?a review