In my family it seems that we all have some degree of Autism.  I personally am convinced that Autism is genetically linked, and varies in intensity.  From the hardly effected at all high functioning person with Aspergers syndrome, to those who will need care for life.  In my family we have a wide spread of that spectrum.  In particular, my sister who was diagnosed with Autism and treated in elementary school as if that always meant low function. 
My sister was diagnosed with Autism at the age of about 6.  She seemed normal then regressed in certain ways.  The public school system where we live is/was kind of backwards about special needs/exceptional children.