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.