As stated above, low income can result in all the other conditions. Obviously, household income isn't a cause of autism, so you need to find the cause of low income.
Could it be autism or asperger's? Affected social skills, introversion, and other "quirks" could very well result in someone being unable to hold or progress financially in a job, forcing them to stay in a low-income area. And has been suggested in the Silicon Valley, when you put a bunch of people with asperger's together, the likelihood of them pairing up increases. If that's the case, then the cause becomes genetic, not environmental. The environment is simply a symptom of the problem.