These four events repeat every 'tropical' year (365 days, 5 hours, 49 minutes), so they become later by about six hours, or (if there has been an intervening leap day) earlier by about 18 hours, from one year to the next.
The three distinctive signs and symptoms of autism include problems with verbal and nonverbal communication, difficulties with social interaction, and repetitive behaviors or narrow, obsessive interests. There are three distinctive symptoms of autism.
It is important to understand that autism is a label for people who have a certain set of symptoms (impairments in social skills, language, and behavior). The label of autism does not explain the cause of autism, and it is likely that multiple factors can contribute to the symptoms of autism.