Autism Spectrum Disorder is a complex disorder that affects thinking, feeling, language, and an ability to relate to others. The effects and severity vary from one person to the next. Symptoms usually present by age 3; mothers of babies with ASD frequently comment on lack of bonding or notice issues with pre-lingual reciprocity, such as babbling or back-and-forth vocalizations (such as cooing).
Regressive autism occurs when a child seems to be developing normally, but around the age of 15-30 months, there is a loss of language or social skills. I bring this up because I have a nonverbal student with ASD who, according to parents, spoke until they moved back to Ethiopia for two years. Every English learner I service has a different story, with respect to the language or languages spoken in the home. I found it interesting that he lost the ability to speak around the time he moved, whether the amount of English or Oromo in the home changed or not.
Autism Parenting Magazine provides a description and facts about Regressive Autism for those who want to read more about it.