IAN twin study observations

The sibling recurrance risk for autism is reported as between 2 - 8%.

http://www.ncbi.nlm.nih.gov/pubmed/15121991

The IAN twin study reported that 31% of fraternal twins are concordant for any ASD diagnosis.

http://www.ncbi.nlm.nih.gov/pubmed/19805709

If autism is genetically predetermined than concordance rates in fraternal twins should be identical to sibling recurrance rates, but it is not.

If IAN concordance rates for fraternal twins is correct than the risk for autism in fraternal twins is beteen four and ten times greater than the risk for autism in siblings.

The Ian twin study therefore can be interpreted as suggesting that the environmental component in autism is both strongly understated and poorly understood.

Connie;

Does IAN have any statistics on sibling recurrance rates in your data base?

It would be interesting to compare the fraternal twin concordance rates of 31% to sibling recurrance rates.

Thanks

Interesting thoughts, RAJ.

One other notion that may further complicate the genetic/environmental picture is the possible existence of different subtypes of autism. (Recently, I have heard people refer to it as "autisms" to acknowledge this possibility.) If there are different conditions that look alike in terms of a person's behavior and challenges but are not alike biologically, we may have some types of ASD that are "more genetic" than others. In that case, sibling recurrence risk and other metrics would be different for each kind of autism. The role environment might play could then be variable, as well.