Easy answers about the etiology of autism continue to elude scientists. But emerging evidence on the growing number of autism spectrum disorder diagnoses and the trajectories of children with autism highlights the need for early diagnosis and access to treatment, particularly for minorities or economically disadvantaged families.
More children are being identified as having autism spectrum disorders, as studies probe the developmental trajectories of patients with autism.
In late March, the US Centers for Disease Control and Prevention (CDC) released the newest estimates of prevalence of autism spectrum disorders in the United States, which suggest a 78% increase in the prevalence of these disorders since 2002 (http://www.cdc.gov/Features/CountingAutism/). The CDC now estimates there were 11.4 cases of these disorders per 1000 children at 8 years of age in 2008, compared with 6.4 per 1000 in 2002.
“We know that people want answers to what's causing this, and so do we,” said Coleen A. Boyle, PhD, MSHyg, director of the CDC's National Center on Birth Defects and Developmental Disabilities, at a press briefing about the findings.
The evidence hints that much of the increase is likely the result of better identification of children with these disorders, said CDC Director Thomas R. Frieden, MD, MPH, at the briefing. For example, more of the children being identified as having autism spectrum disorders have higher cognitive abilities, said Susan Hyman, MD, chair of the autism subcommittee of the American Academy of Pediatrics (AAP), at the briefing. Additionally, more children are being identified in the community vs practice settings, suggesting greater community awareness of the disorder, Boyle noted.
The rapid growth in the prevalence of autism and related disorders among minorities, who have historically had lower rates of autism diagnoses, also suggests a trend of better diagnosis. The CDC found a 91% increase in the estimated prevalence among black children (from 5.5 to 10.5 per 1000) and 110% increase among Hispanic children (from 3.7 to 7.7 per 1000), compared with a 70% increase among white children (from 7.0 to 11.9 per 1000).
More studies are needed to determine the relative contribution of better diagnosis and whether other factors may also be driving the increase, Hyman noted.
One trend identified by the study was that children are being diagnosed earlier. In 2008, for example, the average age at diagnosis was 4 years, compared with 4.5 years in 2006. But Boyle argued that this is still not early enough to allow children to reap the full benefits of early intervention.
“There is a growing body of research that tells us that the earlier a child with autism is identified and connected to services, the more the child will benefit from intervention,” she said.
Parents who suspect their children may not be developing typically should discuss their concerns with their child's physician. The CDC has tools online (http://www.cdc.gov/ncbddd/actearly/index.html) that can help parents make sure their child is on track developmentally. Hyman noted that the AAP recommends physicians screen all children by 18 to 24 months.
Most children with autism do make small strides in their social and communication skills over time, with those children who have the least severe symptoms showing the greatest improvements over time, according to a team of researchers from Columbia University in New York City who charted the developmental trajectories of nearly 7000 children with an autism diagnosis in California (Fountain C et al. Pediatrics. doi: 10.1542/peds.2011-1601 [published online April 2, 2012]). A small subset of about 10% of children with the disorder—whom the study dubbed “bloomers”—make extraordinary developmental gains and move from a low-functioning status to a high-functioning one.
The new findings reinforce that autism is a very heterogeneous disorder, explained Christine Fountain, PhD, lead author of the study, and they raise concerns about socioeconomic disparities in children's access to care. Overall, the researchers found that white children with well-educated mothers were more likely to be high-functioning than minority children with mothers who had a lower level of education. Children with intellectual disabilities were also more likely to be on the low-functioning end of the spectrum.
These disparities were particularly acute among the bloomers. Fountain explained that these children were very unlikely to have comorbid learning disabilities or a mother with a high school education or less. The data didn't contain information about the types of treatment children received, and Fountain said it wasn't clear if the differences in the bloomers group reflected a different etiology of autism or the treatments those children received.
“It's probably both,” she said. “With the economic differences, it is less likely to be a biological difference alone.”
She argued that more randomized trials of therapies are needed to help clinicians identify the most effective treatments and to determine if a particular treatment can shift a child from one trajectory to another. In the meantime, however, it is important for clinicians to identify children early and to ensure that children are referred to appropriate treatment, especially if the child comes from a socioeconomically disadvantaged background.
Kuehn BM. Data on Autism Prevalence, Trajectories Illuminate Socioeconomic Disparities. JAMA. 2012;307(20):2137-2138. doi:10.1001/jama.2012.3916