Ultimate, Unchecked, Unfounded Autism Assumptions: Autism Isn't Really Increasing, It's All Genetic

".... is one of the 1 percent of children in the U.S. born with autism, a complex developmental disability that affects a person's ability to communicate and interact with others at varying degrees. Autism appears to be increasing because of the psychological testing that is available to detect it, said Ramona Puget, who earned a bachelor of arts in psychology and is the president of the Kern Autism Society, a local chapter in the national organization of the Autism Society.  ...There is no known single cause for autism, but it is accepted that it's caused by abnormalities in brain structure or function, according to the research. It is a neurological disorder that is present at birth, but symptoms may not appear until much later      "  

Lodi News-Sentinel, November 26, 2011  [underlining added -HLD]

Really? Can someone help me here?

What conclusive studies have been conducted to determine that autism is increasing because of a) diagnostic changes (last significant changes in 1994) b) increased availability of testing to detect autism c) increased social awareness d) pressure to obtain autism diagnosis to access autism services and treatment? 

If there is no known single cause for autism, or for the autisms, as other sources will often say, how do we know that autism is present at birth or that autism is not really increasing, that it is only ascertainment factors that are creating a false impression of increases in autism disorders? Some very credible sources have pointed to the likelihood of genetic environmental interaction as the source of autism disorders.  Most autism research has focused on the genetic side of the equation with little effort made to "ascertain" potential environmental causes or triggers of the various autism disorders.

So how can it be said that autism is not really increasing or that autism is present at birth?  Surely there are enough controversies in autism discussions without reviving the assumption that autism disorders are 100% genetic and are never caused or triggered by environmental factors?