CATS

The California Autism Twin Study (CATS)has released some of its inital findings. This study will be the largest population based twin study ever attempted. Th study has closed its recruiting phase with 225 pairs of twins recruited from the California Division of Special Services.

Abrahams & Geshwind reported, based on personal correspondance with the prinicpal investigator (Joachim Hallmeyer) that "Unpublished estimates for concordance rates for autistic disorder among dizygotic twins may be as high as 25% (J. Hallmayer, personal communication)".

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2756414/?tool=pubmed

The initial finding confirms the IAN twin study which reported a concordance rate for fraternal twins of 30%.

A small British twin study (Bailey et al 1995) published in 1995 is the most referenced article published in the last two decades and forms the basis for the concept of autism as being genetically predermined. The authors state that they had recruited all twins pairs in England and failed to find a single case of concordant fraternal twins.

http://www.ncbi.nlm.nih.gov/pubmed/7792363

The CATS study is the first to record chorion type in the twins. It has been assumed that all identical twins share the same prenatal environment. This is not the case. In fact, 2/3rds of identical twins do share the same prenatal environment (single placenta), however 1/3rd of identical twins do not share the same prenatal environment (seperate placenta).

Segregating concordance rates in identical twins by chorion type will test the genetic theory. If concordance rates in identical twins segregated by chorion type are the same, then genetics play a dominant role in autism etiology. If concordance rates are significantly higher in identical twins who share the same prenatal envirnment (single placenta) compared to identical twins who did not share the same prenatal environment (seperate placenta) then the results will provide the first strong evidence that the prenatal environment is as, or more, important than zygosity.

Thanks for the information, RAJ.

I will look forward to reading the results of the CATS study in detail when their article is published.