Researchers have found that the pattern of development differs over the first 3 years of life between children with early- and later-onset autism spectrum disorder (ASD).
A prospective longitudinal study of 204 infant siblings of children with ASD and 31 infants with no family history of ASD showed that language, social, and motor development at 6 months were similar between children who were later diagnosed with ASD, those who were diagnosed early with ASD, and those who were not.
However, at 14 and 18 months, Rebecca Landa (Kennedy Krieger Institute, Baltimore, Maryland, USA) and team found that children who were diagnosed early showed slower development than those who were diagnosed late. By 24-36 months, the two groups showed similar levels of development.
Previous research by scientists at the Kennedy Krieger Institute showed that approximately half of all children with ASD can be diagnosed by their first birthday, while the remaining half do not show signs of the disorder until later.
The current study showed that the 28 children with early ASD (diagnosed with ASD at 36 months, received clinical judgment of ASD symptomology at 14 months) showed significantly lower expressive language and shared social smiling scores at 14 months than the later-ASD group (n=26; diagnosed with ASD at 36 months without showing earlier ASD symptomology).
By 18 months, the early-ASD group showed greater delays in receptive and expressive language development compared with the late-ASD group, while at 24 months this gap between the groups had closed due to increasing impairment in the late-ASD group. At 30 and 36 months, there was no significant difference in development between the early and late groups.
The analysis also showed that at 14 months, children in the late ASD group scored significantly lower than the 181 children without ASD for fine motor and some language skills.
"Results show that ASD has a preclinical phase when detecting it may be difficult," explained Landa in a press statement. "In some children with ASD, early signs of developmental disruption may not be ASD-specific."
She suggested the routine administration of general development screeners, such as the Ages and Stages Questionnaire, beginning in infancy, and complemented with ASD-specific screeners by 14 months. "Screening should be repeated through early childhood. If concerning signs of delay associated with ASD are observed in a child who scores normally on standardized tests, further assessment is warranted," she recommended.
"If parents aren't seeing their children steadily develop new skills, they should talk to their pediatrician or contact their local early intervention program," advised Landa. "Results from this study show that communication delays are often present in the second year of life in children with autism, especially involving language comprehension."
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