I would like to remind HN that autism being a syndrome, it is likely to be several distinct illnesses with different genetic and environmental factors.
That's not correct. If something is a syndrome it is more likely to be a single distinct illness rather than multiple distinct ones.
I.e., suppose 50% of people suffer headaches, 50% suffer nausea, and 50% suffer aching back. Further, suppose 12.5% (= 50% x 50% x 50%) of people suffer all three symptoms - in this case, the three symptoms put together are NOT a syndrome.
On the other hand, suppose 40% of people suffered headaches, nausea and aching back together. In that case the three symptoms together are a syndrome.
A syndrome is probabilistic evidence that there is an underlying cause of multiple co-occurring symptoms.
You are right, I should have written more explanations. Autism is quite special in that the symptoms are behavioral: impairments in social interaction and communication, restricted interests and repetitive behavior (this list is on Wikipedia). These are very different from aches and other simple physical manifestations. In fact, when we try to look for simpler symptoms, the set of symptoms becomes blur, in that no other symptom can be found always present together with to those core behavioral ones. The variety of more physical manifestations of autism hints at a variety of root causes. E.g., gastrointestinal issues are common but not always there. Cerebellar anomalies too. etc...
Sorry, I wrote that up fast, if you are interested you can write a reply, I'll try answering tomorrow, it's late for me now.
Really, I must insist: a syndrome is a set of clinical symptoms. "Austism" describes a set of symptoms. "Autism" does not describe an illness with a well-defines root cause. Hence, my comment: autism is a syndrome, and there could be several distinct illnesses (several root causes) that lead to autism.
