I'm very sorry to hear about your child.
It is also sad that parents feel they can't tell their stories. I've heard from a mom, a psychologist, who felt that way even AFTER they received compensation from the national vaccine court! The system is SO sick. The greed of Big Pharma and their friends in politics and mainstream media is despicable.
Since "autism" is a list of symptoms, a label, there can be any number of causes or contributing factors. Genetics of course is one.
You might be interested in this old discussion between Dr Amy Holmes and some members of an autism support group on the subject of timing.
Born Autistic or Born Poisoned? That is the question?
http://onibasu.com/archives/am/7539.html
Thankfully Dr Amy's son improved enough that he lost his ASD label.
http://onibasu.com/archives/am/4930.html
Bernie Rimland mentioned in the above discussion is the founder of the Autism Research Institute.
Autism Research Institute treatment parent ratings 2009
http://www.autism.com/index.php/treatment_ratings_asd
"Detox. (chelation)" 74% report "got better", 3% report "got worse", 23% report "no effect"
The 74% rating is the best of the many dozens of listed interventions.
Maybe your child had a setback after receiving the MMR vaccine that does not include mercury. That does not mean heavy metals were not involved indirectly as a contributing factor.
HMs from mom's
Amalgam fillings, flu shot given to pregnant women, etc affect the immune system and other systems. When your child received the vaccine his immune system was not able to handle the attenuated vaccine.
Don't give up hope for additional gains even if you were told not to expect them! This mom continued to fight for her son's health and was rewarded for her admirable efforts. I followed her frequent posts in an autism support group for a few years.
https://groups.yahoo.com/neo/groups/Autism-Mercury/conversations/messages/315815
http://health.groups.yahoo.com/group/Autism-Mercury/message/292717
https://groups.yahoo.com/neo/groups/Autism-Mercury/conversations/topics/304450
Have you checked out any of the information from Dr Marco Ruggiero on the gut and microbiome? I'm not suggesting it is the cure but I've heard from some that it gave them a boost and enabled them to better tolerate other treatments.