In the largest prospective study to date of children with early and later manifestation of autism spectrum disorders (ASD) compared to children without ASD, researchers found two distinct patterns of language, social and motor development in the children with ASD. Published in the journal Child Development, the study found that early in development, children who display early signs of ASD show greater initial delay across multiple aspects of development compared to children whose ASD symptoms emerge later. However at 36 months of age, the early differences between these groups are no longer obvious. By the third birthday, the level of impairment between these symptom onset groups of children with ASD is comparable. Additionally, researchers uncovered a preclinical phase of ASD in which the signs of delay are not easily detected with existing clinical tests.
Previous research by Kennedy Krieger Institute researchers found that approximately half of all children with ASD can be diagnosed around the first birthday, while the remaining half do not show diagnostic indicators until later. The current study builds upon these findings by further evaluating motor and language development in a wider age span of children diagnosed with ASD (6 to 36 months), and examining how development unfolds differently in each group.
“Regardless of diagnosis, the development of children with and without ASD appears similar at six months of age on clinical tests,” says Dr. Rebecca Landa, lead author and director of Kennedy Krieger’s Center for Autism and Related Disorders. “However, for those children who went on to develop autism, the earliest signs of atypical development were non-specific to autism, such as general communication or motor delay.”
About the Study
Participants included 204 infant siblings of children with ASD, who are at a higher genetic risk for developing ASD, and 31 infants with no family history of ASD. The infants were examined at 6, 14, 18, 24, 30 and 36 months of age. Confirmation of ASD classification was made at the 30 or 36 month visit for all participants because diagnosis at this age is considered definitive. At each visit, researchers evaluated the infants for motor, language, communication, social-affective and symbolic abilities, as well as typical symptoms of ASD.
Based on gold standard ASD assessments, infants were divided into three groups: Early-ASD, Later-ASD and Non-ASD. Both ASD groups (54 infants total) were confirmed to have ASD at 36 months; however the Early-ASD group (28 infants) received a clinical judgment of ASD symptomology at 14 months, whereas the Later-ASD group (26 infants) did not. The Non-ASD group (181 infants) did not meet outcome criteria for ASD.
Early-ASD versus Later-ASD
- By 14 months, the Early-ASD group exhibited significantly lower expressive language and shared social smiling scores than the Later-ASD group.
- By 18 months, the Early-ASD group exhibited greater delays in receptive and expressive language development compared to the Later-ASD group.
- At 24 months, this gap between the Early- and Later-ASD groups had closed due to increasing impairment in the later-ASD group.
- At 30 and 36 months, there were no detectable differences between the Early- and Later-ASD groups.
Early-ASD versus Non-ASD groups
- At 6 months, the Early-ASD and Non-ASD groups exhibited comparable development.
- At 14 months, the Early-ASD group diverged from Non-ASD development in all measured aspects of development, except for fine motor functioning.
- These differences were sustained through 36 months.
Later-ASD versus Non-ASD groups
- At 6 months, the Later-ASD and Non-ASD groups exhibited comparable development.
- At 14 months, the Later-ASD group’s scores were significantly lower than the Non-ASD group’s for fine motor and some language skills.
- At 24 and 36 months, the Later-ASD group performed below the Non-ASD group on all abilities examined except fine motor functioning at 24 months.
Dr. Landa noted that patterns of slowing, plateauing and decline in development in children with ASD occurred within the timeframe when parents report first concerns about children with ASD. The subtlety of early signs and a gradual shift from typical development may not be detected by ASD screeners or by health professionals in a brief office visit. Thus, parent’s expression of concern about their toddler’s development or behavior requires careful consideration.
“If parents aren’t seeing their children steadily develop new skills, they should talk to their pediatrician or contact their local early intervention program,” says Dr. 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.”
Further research is needed with a larger population of children with ASD and using behavioral and biological measures that may detect more subtle indicators of disrupted development in children with ASD in the first year of life. With larger studies, researchers can conduct more detailed analyses of developmental advances in children with ASD, which may facilitate the development of better early ASD screening tools and thereby improving access to earlier intervention. Studies have shown that early intervention improves language, social and cognitive outcomes for children with ASD.
The study was funded by the National Institute of Mental Health, the National Institutes of Health, and Autism Speaks.
Kennedy Krieger Institute