By 12 months: Little or no babbling; little or no back-and-forth gestures such as pointing, showing, reaching or waving; and little or no response to name. By 16 months: Very few or no words. By 24 months: Very few or no meaningful, two-word phrases. At any age: Loss of previously acquired speech, babbling or social skills; avoidance of eye contact; persistent preference for solitude; difficulty understanding other people’s feelings; persistent repetition of words or phrases, resistance to minor changes in routine or surroundings; repetitive behaviors (flapping, rocking, spinning, etc.); and unusual and intense reactions to sounds, smells, tastes, textures, lights and/or colors.