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.
For others, symptoms may be more severe, as when repetitive behaviors and lack of spoken language interfere with everyday life. As illustrated by the graph below, the basic symptoms of autism are often accompanied by other medical conditions and challenges.