As Geralding Dawson of Autism Speaks says "What we see in autism may be partly the result of not engaging with the social environment. So if you engage the baby through an intervention, you might prevent or at least reduce the development of autism symptoms."
Among the telltale signs of trouble at 12 months: not responding to one's name; not sharing interests through pointing and eye gaze; lack of joyful expression; an absence of babbling; difficulty establishing eye contact; and staring too long at inanimate objects (see FirstSigns.org )
This is an interesting article and well worth reading
Researchers Find First Signs of Autism Even in Infancy - TIME.