Okay. First of all autism is a spectrum. Everyone falls on the autism spectrum. Take something like Anti Social Personality Disorder, or psychopathy people would also score somewhere on a spectrum there. Take a look at the PCL-R test. What you call a personality disorder what you want. We have extremely little understanding of these disorders and ultimately we just see that some unhealthy traits seem to come together frequently and then we call it a PD. It is worth noting that many disorder frequently co exist e.g bipolar disorder and Borderline PD, suggesting maybe a whole new diagnosis if you wanted to think like that. Ultimately disorders just explain symptoms, not causes. We probably just identify autism separately because it is so clear and measurable. There is ambiguity with PDs between the individuals ‘self’ and what is consequence of a ‘disorder’. I am a final year psychology student. Someone else can correct me if they disagree. But ultimately we draw arbitrary points on spectrums at which we say something is dysfunctional enough to call a disorder. It doesn’t matter too much how you categorise. It is also worth many disorders are diagnosed by behaviour and not feelings or cognition. We can assume on causes the other but you can get different causes for the same behaviour. Because of lack of understanding PDs should be understood as a tendency for certain behaviours and it says no more. With autism the research is much more established.