Part of the impetus for the fringe belief that vaccines are somehow causally related to the development of autism is that the signs of autism often become apparent at 2-3 years of age, after children have received many of their routine childhood vaccinations. (Average age at diagnosis is 3.1 years.) In an otherwise healthy child, the vaccines might be the only thing the parents can think of that could be a potential cause.

Signs of autism are not clinically noticeable prior to 6 months of age. From about 6-18 months the signs can be detected by careful clinical observation, but may be missed by parents. During this time parents may become slowly aware that their child is not developing as expected, and the creeping suspicion that something is not quite right often culminates in a diagnosis between age 2-3.

The phenomenon of temporal binding may then cause the parent’s memories to shift over time so that the temporal correlation between getting vaccines and signs of autism appearing become closer together. For some parents this can become a very powerful memory – my child was perfectly normal, then he received vaccines and started to show signs of autism.

Meanwhile evidence is mounting that autism spectrum disorder, while heterogeneous, is dominantly the result of genetic predisposition. Changes involving many genes that are involved with brain development have been implicated in autism risk. This does not rule out epigenetic and environmental factors, but the evidence does strongly point to the fact that autism is largely a group of genetic disorders.

If the genetic theory of autism is true then it becomes possible, even probable, that signs of autism will be present even at birth. Although, autism likely represents an alternate developmental pathway for the brain, and so autistic and typical children will become increasingly divergent as their brains develop. The point at which that divergence begins or becomes apparent is not necessarily at birth or in the womb.

Until now the earliest signs of autism could be detected at about 6 months of age, including multiple clinical and MRI studies.  Six months seemed to be the consistent time at which the divergence between autistic and typical brain development becomes apparent.

However, a new study pushes that time back to only 2 months. This is a small study, and should be considered preliminary, but the findings are interesting. Researchers used eye tracking technology to quantify the degree to which infants, mostly in a high risk group for autism, looked at the faces and eyes of people in their environment. One of the hallmark clinical signs of autism is that children are less social and they do not make as much eye contact as typical children.

The researchers found that those children in their study who would later be diagnosed with autism spent less time looking at faces and eyes than children who were not later diagnosed with autism. If this result holds up to replication, it will be the first study to demonstrate clinical signs of autism earlier than six months.

The researchers found no difference prior to two months, and also they found that eye contact in children later diagnosed as autistic decreased steadily from 2 to 6 months of age. This correlates with autism being a divergent pathway of brain development occurring over time.

The researchers were a bit surprised that the autistic and typical children were not already diverging at birth, but finding that the divergence is not apparent until 2 months is still compatible with a genetically determined developmental disorder. They also suggest that their results might indicate a window of treatment opportunity – if high risk children are treated prior to 6 months of age perhaps the potential for a treatment response would be greater. Whether or not brain development in autism can be altered by any currently available treatment remains to be seen.

Given prior research it seemed likely that more sensitive techniques would push the age of earliest detection to prior to 6 months, and now, perhaps, it has. I am curious to find out if 2 months is the true earliest clinical manifestation of autism, or if other or more sensitive techniques will ever push it back to birth, or even in the womb.

It’s possible that the brain simply has not developed enough prior to 2 months of age for any behavior differences, no matter how subtle, to manifest. Brain imaging techniques, however, may still find subtle differences.

This is just one baby step, but it represent the relentless and continued march of the scientific evidence toward the conclusion that autism is a complex set of genetically determined brain development disorders, and away from the hypothesis that vaccines are playing any role.