Infant Sibs Project

The first research has been published. The theory is that closely following babies born in families with a child previously diagnosed with autism would shed light on the genetic transmission of autism.

This study examined the infant sibs beginning at six months of age and tracked their subsequent development 18 months later (2 years of age).

None of the infant sibs who showed lower levels of eye contact at six months were autistic at outcome. The study did show that eye contact at six months was not predictive of autism but was predictive of differences in language development.

http://www.ncbi.nlm.nih.gov/pubmed/19702771?

This first study is a blow to the genetic theorists who predicted that autism can be detected as early as six months of age, it cannot.

The study also adds evidence to the gene-environment interaction model. What has been described as autistic-like traits in unaffected family members, traits such as lower eye gaze, a higher rate of reserved personality types, differences in cognitive and language styles are all normal variants of human behavior.

This is evidence for a two hit mechanism operating in an autism subgroup. Affected and unaffected family members may share a clustering of what has been described as 'autistic-like' traits. Traits that are perfectly normal variences of human behavior.

What may seperate affected and unaffected family members is not a shared clustering
of normal trait variances but rather the underlying structual abnormalities in brain development (a two hit mechanism), present in affected family members but absent in unaffected family members.

Autistic-like traits may be highly heritable, but autism per se is not since it is associated with unfavorable events in the pre, peri and neonatal period that are associated with risk for a disruption in early brain devlopment.

http://pediatrics.aappublications.org/cgi/content/full/107/4/e63#T1

Fascinating study. Thank you for bringing it to our our readers' attention, RAJ.

One thing to keep in mind is that this is only one study, and it involved only 3 "turned out to have autism" children. In effect, they only had 3 children whose early development might have provided a clue to earliest signs of autism. As they point out in the paper, from all we know so far, autism does not show up in the same way for all children. Some are different from birth; some develop normally and then regress, either slowly or all at once. The authors said:

"Therefore, it may be that we failed to see abnormal gaze and affect at 6 months in the three infants from our sample who developed autism not because gaze and affect are unimportant to the early
identification of autism, but because the process of
symptom onset had simply not yet begun for any of
these three infants at 6 months."

What will be so important to the future of autism research is the identification of subtypes of autism, some of which may be very heritable (that is, genetic) and others that may be much more complex, including the "two-hit" model that RAJ explained above. If there are really different kinds of autism, it may be hard to find predictive patterns in younger sibs until we know what kind of autism the older sib had.