There are many, many hypotheses and studies surrounding autism spectrum disorders and it seems that most everyone has their pet favorite. I am going to try and summarize in fairly simple layperson's terms what I understand as the various possible causes being explored and some of the types of treatments:
Autism spectrum disorders seem to be complex and there are probably several causes. Part, if not all, of the reason for the dramatic rise in the numbers of people with ASD is changes in diagnostic practice; i.e. it is diagnosed more but that is not proof that more people than ever actually have the symptoms.
Twin studies have shown there is a strong genetic link with autism. It does run in families, but that is not the only factor. How it is inherited is complex and unknown at this point.
It is believed that environmental factors play a role; especially early exposure to environmental insult that affects the developing brain. Some possibilities being studied are: thiomersal, a preservative in vaccines; heavy metals, plastics, pesticides, etc.
Leaky gut syndrome is believed to possibly contribute to autism by allowing poorly digested food substances to leak into the blood stream causing brain damage or immune system reaction. Also, poor digestion is believed to lead to overgrowth of fungi, bacteria, and yeast which may cause a destructive auto-immune reaction.
Vitamin D deficiency may be a cause, which I mentioned in an earlier post. See the vitamindcouncil.org also.
Excessive hygiene has been considered as a possible contributing factor. In other words, by being too clean we rob our childrens' immune systems of the opportunity to develop normally through everyday exposure to germs. This may result in a weak immune system or auto-immune disease.
Some also believe that when it comes to high functioning autism and Aspergers that it is not an objective determination and therefore is basically a social construction of our society that defines "normal" in certain ways. Those who are socially outside those constructed norms fall within the realm of pathology. In this same vein, high functioning and Aspergers could be considered a purely psychiatric illness.
Various treatments to de-toxify or heal the immune system are being used or advocated. Treatments to kill off yeast and anaroebic bacteria, as well as potent anti-fungals are used to promote die off of harmful microbes in the intestinal tract.
Restrictive diets to avoid adverse food reactions or food allergy reactions; such as gluten-free, casein-free, preservative & dye-free, and sugar-free.
Vitamin supplements in larger than typical doses.
Also sensory therapy, auditory therapy, occupational and play therapy, behavior modification therapy, and psychotherapy.
And finally there are those who are anti-vaccinations.
I hope I got most of that right. You can enter just about any of these terms along with "autism" into your favorite search engine to get a lot more details.
My son his on the spectrum but high-functioning and quite intelligent. Personally, I will try it if it's not too expensive and doesn't seem like it could be harmful. You don't know if it will help until you try it.
I don't like the idea of giving my child potent anti-fungals, anti-virals, etc. to promote "die-offs". I can't afford too much therapy, but have done some and try to work with him on his social skills and his communication/language skills. I do give my son a good multi-vitamin plus extra vitamin D. I also gave him digestive enzymes for awhile. He does have a diary allergy and so he is on a dairy-free diet. He takes medication for his obvious ADHD symptoms.
Otherwise, I mostly like to find what interests him and draw him out that way. I like to give him opportunities to learn and exercise his brain. He loves video games and computers, so I buy him lots of educational CD-ROM games as well as a few just-for-fun games. He pretty much obsesses over numbers, so I use numbers to teach him whenever I can. I also have encouraged his interest in numbers by getting him into Math. I get him Sudoku books, math workbooks above his grade level, calculators, protractors, measuring tapes, calendars, etc.
He also likes logical and strategic board games, so I got my Dad to teach him to play Chess. This is a great way for him to practice some of his reciprocal social skills one-on-one with the game as a way to keep him interested.