No one appears to know exactly what causes Autism. We do know is that the ratio went from affecting 1/10,000 children back in the 1980s to being diagnosed in 1/45 children today.
"In 2014, 1 in 45 children have been diagnosed with ASD." Ref: CDC
Although there are investigations to try and determine the genetic markers relative to Autism. My suspicion is that eventually we will find an environmental root cause.
For example we may find that dental amalgam mercury fillings destroy a vital piece of genetic code in prenatal development or, that our genetically modified foods or insecticides used to protect crops have an impact.
I have collected a list of Genes that Science has marked as being of Interest relative to Autism Studies:
The most common mentions I see state that on Chromosome 16 there is a huge string of missing genetic code and a scrambled gene next to the SEMA5A Gene on Chromosome 5 that hinders critical brain development. (Although I have also seen referenced to SEMA5A being on Chromosome 6. Not 100% sure which is right)
|Chromosome 4||(4q13)||between CENPC1 and EPHA5|
|Chromosome 5||(5p15)||between SEMA5A and TAS2R1 (SEMA5A is critical to Brain Development and in Autism patients the expression of SEMA5A is diminished)|
|Chromosome 6||(6p23)||in JARID2|
|Chromosome 9||(9q21)||between ZCCHC6 and CCHC, and also in GAS1|
|Chromosome 10||(10q21)||in CTNNA3|
|Chromosome 11||(11p14)||in GAS2|
Children with Autism develop normally until about 12 to 18 months of age. This is when a child's brain develops the ability to regulate the flow of neurons. It is believed that when this is not properly regulated it results in too much neural activity. Once the Diagnosis is made Early intervention is the best response.
Here is a listing by state of contact phone numbers Parents and Families can call for Early Intervention Assistance Programs
Please know that every situation is unique and before implementing any new solution you should seek advice from the professional team that provides care for the loved one that has Autism.