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Researchers have known for years that when one identical twin has autism, the other is also likely to be diagnosed with it – evidence that autism likely has a genetic component.

Researchers at Kennedy Krieger Institute studied 277 pairs of twins and found that when one identical twin had the disorder, the other developed it 88 percent of the time; for fraternal twins, that figure was 31 percent.

Despite this progress in unlocking the mysteries of autism, scientists have simply confirmed that there are likely numerous genetic links to autism.

The study’s major finding was that children with ASD have significantly more CNVs affecting their genes than children without ASD. Children with ASD have 20 percent more CNVs in general, and 70 percent more CNVs impacting genes known to be associated with ASD or cognitive problems. Significantly, many of the genes that are affected control important functions such as cell proliferation and cell-to-cell communication.

Some of the newly discovered genetic variants are inherited, and are found in parents or siblings of children with them. Others, however, seem to have originated spontaneously in the affected child, and do not appear in other family members.

While these findings add significantly to the scientific understanding of the genetic and biological underpinnings of ASD, the immediate usefulness is limited. That’s because there are a very large number of CNVs, and each child shows a different pattern of genetic changes. Each of these changes is rare; no CNV showed up in more than one percent of the children studied.

The results show for the first time the role of the SYN1 gene in autism, in addition to epilepsy, and strengthen the hypothesis that a deregulation of the function of synapse because of this mutation is the cause of both diseases

until now, no other genetic study of humans has made this demonstration.

The different forms of autism are often genetic in origin and nearly a third of people with autism also suffer from epilepsy.

The Howard Hughes Medical Institute describes how researchers using "high-throughput gene sequencing technology" were able to identify several de novo or spontaneous gene mutations in 20 children with sporadic autism spectrum disorders -- that is, their family members showed no other sign of autism.

The team identified 21 spontaneous mutations -- meaning they weren't inherited from either parent -- in the children's DNA. Eleven of these were mutations that would alter the protein encoded by the affected gene. In four of the 20 children, the researchers found mutations that were severe, some of which have been previously linked to autism, intellectual disability, and epilepsy.

one child had a mutation in the GRIN2B gene, which is crucial for neuronal signaling.

The type of mercury used in thimerosal is generally cleared from the body within six weeks, which in theory would render it harmless. But according to those researchers who believe that the preservative causes autism, babies born during that 20-year window were injected with many times the "safe" level as determined by the FDA -- and some, they feel, were genetically incapable of clearing the doses of mercury from their bodies. Mercury is, in fact, a neurotoxin, and the theory is that the recent leap in autism diagnoses can be directly tied to thimerosal.

In 2004, the Institute of Medicine undertook a comprehensive review of all the published literature on thimerosal and autism and concluded that the available evidence demonstrate that there was no link. The CDC launched a series of studies that examined the relationship between the incidence of autism and the amount of mercury a child received in the first 6 months of life and also found no relationship. Although all published credible studies have found no link between thimerosal and autism, some continue to be unconvinced.

At present, the thimerosal controversy continues, even though the removal of thimerosal from vaccines has not resulted in lower rates of autism diagnoses.