ASD in Down syndrome

Criteria of ASD are often applied to individuals with Down syndrome even though the validity of the criteria in this population is unclear. About 5% of individuals with Down syndrome exhibit repetitive stereotypic movements, but do they also have social communication deficits? There is also a greater incidence of intellectual disability in Down syndrome, that may cloud or confuse diagnosis of social communication skills. A recent report from the Kennedy Kreiger details the co-mobities. The importance of making these distinctions means that more appropriate interventions can be trialled. The other interesting observation comes from a consideration of the genetics. In Down syndrome, over 350 genes are present in excess on chromosome 21, compared to one gene in deficit in ASD, for example. This results in a reduced brain size in Down syndrome, but potentially increased brain size in ASD. What is particularly interesting is that 40% of individuals with Down syndrome have ASD (either PDD or autism). Therefore, despite (nearly all) individuals with Down syndrome having a defined and consistent genetic imbalance, not all of them develop ASD, motor stereotypies or display disruptive behaviour. The question now for researchers is Why? The challenge raised by the authors of the above study for educators is to develop a range of targetted interventions.