But that can be studied. Scientists can repeat the study with autistic children who have not lived with the condition for decades, even if by just using EEGs as suggested in the article. If the mGlu5 deficit in autistic children is comparable to the deficit in autistic adults then that would strongly suggest that the deficit occurred during one period at a young age, rather than occurring over years as a result living with the condition.

Also, I assume that the deficit could be assessed from donated brain tissue. There is a group (https://www.autismbrainnet.org/) that has been encouraging the parents of autistic children who have passed away to donate tissue for research. If researchers can establish that the mGlu5 deficit exists at comparable levels in the youngest donors, it would indicate that the deficit occurs at a very young age. Perhaps during paring or myelination.