Children with Down syndrome can be diagnosed with autism via the autism spectrum disorder criteria from the Diagnostic and Statistical Manual of Mental Disorders, based on results of a cluster analysis of 293 children with Down syndrome.
Previous studies have suggested that autism spectrum disorders (ASD) can’t be effectively diagnosed in children with Down syndrome (DS) because of the cognitive impairment already associated with DS, said Dr. N.Y. Ji of Johns Hopkins University, Baltimore.
In this study, Dr. Ji and colleagues used the Aberrant Behavior Checklist to show that children with both DS and ASD match the DSM criteria for autism diagnoses (J. Intellect. Disabil. Res. 2011 Aug. 30 [doi:10.1111/j.1365-2788.2011.0465.x]).
The researchers assessed more than 1,000 children aged 0-21 years who visited the Down syndrome clinic of the Kennedy Krieger Institute in Baltimore during 1992-2008. They identified 293 children for cluster analysis and used the Aberrant Behavior Checklist–Community (ABC-C) and the Autism Behavior Checklist to identify autism features. For comparison, the researchers also identified children with DS and two other common DS comorbidities: disruptive behavior disorder (DBS) and stereotypic movement disorder (SMD).
Overall, 114 children (39%) met criteria for ASD, 104 (36%) met criteria for DBS, and 43 (15%) had SMD. Another 32 children (11%) did not meet criteria for any coexisting major psychiatric condition in addition to DS.
The findings add to the field of Down syndrome research because they confirm the DSM diagnostic criteria of autism spectrum disorder in children with Down syndrome.
The researchers divided the children into four clusters based on the ABC-C and Autism Behavior Checklist.
Participants in clusters 1 and 4 had lower levels of intellectual functioning than did those in clusters 2 and 3, although there was no significant difference in the median age among the groups, the researchers noted.
In addition, children in cluster 1 had a broad range of behavioral problems, including self-injury and highly disruptive behavior.
Children in cluster 2 had the lowest ABC-C scores and the mildest levels of maladaptive behavior.
Children in cluster 3 had high disruptive behavior scores similar to those seen in cluster 1, but significantly less severe autistic behaviors.
Children in cluster 4 had the most severe autistic behaviors, compared with the other clusters.
Children in clusters 1 and 4 underwent additional analysis to confirm that they resembled the original DS plus ASD diagnostic group. This additional analysis confirmed that children with DS and ASD with "more irritable and hyperactive behaviors as well as high levels of self-injury" were more likely to fall into cluster 1, whereas children with more severe autistic behavior fell into cluster 4. In addition, significantly more children in cluster 4 had a history of late onset ASD, compared with those in cluster 1.
"These data also support the existence of ASD subtypes in DS, in line with the heterogeneity of the behavioral disorder in the general population," the researchers noted.
The study was limited by the relatively small number of children in each category and by the use of only the ABC-C data for the primary analysis, the researchers said.
However, the findings add to the field of DS research because they confirm the DSM diagnostic criteria of ASD in children with DS. Additional longitudinal studies could examine whether the DSM diagnoses remain stable over time. Better behavioral instruments are needed to help clinicians recognize comorbidities and suggest targeted interventions, they added.
"We have known for some time that Down syndrome is associated with a range of neurodevelopmental and behavioral outcomes," said Dr. George T. Capone, a study coauthor. "We hypothesized that the association between developmental function and behavior was not random; rather, the two are related in such a manner that distinct behavioral clusters can be identified."
The study underscores the point that children with Down syndrome are not all alike, he explained, which has "direct implications for our understanding of brain organization and possibly the relationship between genotype and phenotype in young children with the diagnosis."
He and his colleagues were not particularly surprised by the findings, he added, because "it has long been our observation that children with Down syndrome and maladaptive behavior differ from their typical peers with the diagnosis." These differences are obvious and measurable both to parents who respond to validated behavioral questionnaires and to neurodevelopmental pediatricians who use a DSM classification to identify behavior and mental health disorders.
Increased vigilance, screening, and evaluation for atypical development and behavior problems have recently received greater emphasis in the American Academy of Pediatrics’ updated "Health Supervision for Children with Down Syndrome" guidelines (Pediatrics 2011 128:393-406).