Summary: Autism diagnosis becomes stable starting at 14 months of age, researchers report. The accurate diagnosis of ASD, four months earlier than previously believed, leads to more opportunities for early interventions.
Diagnoses of autism spectrum disorder (ASD) by trained professionals in children as young as 14 months are remarkably stable, suggesting that accurate screening and earlier treatment is feasible, report scientists at University of California San Diego School of Medicine in a study published online April 29, 2019 in JAMA Pediatrics.
Growing evidence suggests ASD has its origins in prenatal life — most likely during the first or second trimester of pregnancy — and children begin to display symptoms of the condition by their first birthdays, such as failing to respond to their names or positively interact with others.
Early diagnosis of ASD means earlier intervention and improved therapeutic benefit. “The sooner you can address issues of ASD, the better the outcome for the child,” said the study’s first author, Karen Pierce, PhD, professor of neurosciences and co-director of the UC San Diego Autism Center of Excellence. She led the study with senior author Eric Courchesne, PhD, also a professor of neurosciences.
Multiple studies, including research conducted by Pierce, have found that simple parent checklists performed at the child’s first birthday can identify symptoms of ASD. And yet the mean age of ASD diagnoses in the United States, write the researchers, is “often years later, generally between ages three and four.”
Pierce said the lag between the first signs of ASD and diagnosis represents a missed opportunity, particularly given the accelerated pace of brain development in the first years of life.
“Synaptic density or connections between neurons in the prefrontal and temporal cortex, brain regions centrally involved in higher-order social behavior, doubles between birth and one to two years in age,” said Pierce. “It’s conceivable that outcomes for children with autism could be improved if treatment occurred during this period of rapid brain growth, rather than after, which is more commonly the case.”
To conduct their study, Pierce and colleagues assessed 1,269 toddlers from the general population (441 ASD, 828 non-ASD) who received their first diagnostic evaluation between 12 and 36 months and at least one subsequent evaluation, all by licensed psychologists. Diagnoses ranged from ASD and features of ASD to language and developmental delay or other developmental issues.
The overall diagnostic stability for ASD was 0.84, higher than for any other diagnostic group. Only 2 percent of toddlers initially considered to have ASD transitioned to later diagnoses of typical development. Within the group diagnosed with ASD, the most common transition was from ASD to ASD features at 9 percent.
Diagnostic stability of ASD was weakest at 12 to 13 months, just 0.50, but increased to 0.79 by 14 months and 0.83 by 16 months. Twenty-four percent of toddlers were not designated as ASD at their first evaluations, but later identified. The most common transition in this group was an initial designation of developmental delay (25 percent) or language delay (16 percent), transitioning to later-onset ASD.
“Our findings suggest that an ASD diagnosis becomes stable starting at 14 months, and overall is more stable than other diagnoses, such as language or developmental delay,” said Pierce.
“Once a toddler is identified as ASD, there is an extremely low chance that he or she will test within typical levels at age three or four, so it’s imperative that we use every effective tool as early as we can to begin treating diagnosed children to the benefit of them and their families over the long-term.”
Co-authors of this study also include: Vahid Gazestani, Elizabeth Bacon, Cynthia Carter Barnes, Debra Cha, Srinivasa Nalabolu, Linda Lopez, Adrienne Moore, Sunny Pence-Stophaeros, all at UC San Diego.
About this neuroscience research article
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Evaluation of the Diagnostic Stability of the Early Autism Spectrum Disorder Phenotype in the General Population Starting at 12 Months
Importance Universal early screening for autism spectrum disorder (ASD) in primary care is becoming increasingly common and is believed to be a pivotal step toward early treatment. However, the diagnostic stability of ASD in large cohorts from the general population, particularly in those younger than 18 months, is unknown. Changes in the phenotypic expression of ASD across early development compared with toddlers with other delays are also unknown.
Objectives To examine the diagnostic stability of ASD in a large cohort of toddlers starting at 12 months of age and to compare this stability with that of toddlers with other disorders, such as developmental delay.
Design, Setting, and Participants In this prospective cohort study performed from January 1, 2006, to December 31, 2018, a total of 2241 toddlers were referred from the general population through a universal screening program in primary care or community referral. Eligible toddlers received their first diagnostic evaluation between 12 and 36 months of age and had at least 1 subsequent evaluation.
Exposures Diagnosis was denoted after each evaluation visit as ASD, ASD features, language delay, developmental delay, other developmental issue, typical sibling of an ASD proband, or typical development.
Main Outcomes and Measures Diagnostic stability coefficients were calculated within 2-month age bands, and logistic regression models were used to explore the associations of sex, age, diagnosis at first visit, and interval between first and last diagnosis with stability. Toddlers with a non-ASD diagnosis at their first visit diagnosed with ASD at their last were designated as having late-identified ASD.
Results Among the 1269 toddlers included in the study (918 [72.3%] male; median age at first evaluation, 17.6 months [interquartile range, 14.0-24.4 months]; median age at final evaluation, 36.2 months [interquartile range, 33.4-40.9 months]), the overall diagnostic stability for ASD was 0.84 (95% CI, 0.80-0.87), which was higher than any other diagnostic group. Only 7 toddlers (1.8%) initially considered to have ASD transitioned into a final diagnosis of typical development. Diagnostic stability of ASD within the youngest age band (12-13 months) was lowest at 0.50 (95% CI, 0.32-0.69) but increased to 0.79 by 14 months and 0.83 by 16 months (age bands of 12 vs 14 and 16 years; odds ratio, 4.25; 95% CI, 1.59-11.74). A total of 105 toddlers (23.8%) were not designated as having ASD at their first visit but were identified at a later visit.
Conclusions and Relevance The findings suggest that an ASD diagnosis becomes stable starting at 14 months of age and overall is more stable than other diagnostic categories, including language or developmental delay. After a toddler is identified as having ASD, there may be a low chance that he or she will test within typical levels at 3 years of age. This finding opens the opportunity to test the impact of very early-age treatment of ASD.