"High rates of ASD [autism spectrum disorder] and ADHD [attention-deficit hyperactivity disorder] were found: 17 (42%) and 14 (34%) of the 41 children met DSM criteria for ASD and ADHD respectively."
That was the conclusion reached in the study by Ulrika Oxelgren and colleagues  looking at the "prevalence of autism spectrum disorder (ASD) and attention-deficit-hyperactivity disorder (ADHD) in a population-based group of children and adolescents with Down syndrome." The population in this case comprised 60 children and young adults diagnosed with Down's syndrome (Down syndrome if you prefer) and the gold-standards that are the Autism Diagnostic Interview-Revised (ADI-R) and the Autism Diagnostic Observation Schedule (ADOS) were the instruments of choice when arriving at decisions of whether autism might be present or not.
New news? No it's not new news that autism (whether in diagnosis or in traits) may be over-represented when it comes to Down's syndrome (see here and see here for other research-based examples). There has even been a suggestion that regression - a key part of at least some autism - may be part and parcel of some cases of Down's syndrome (see here) too.
Oxelgren et al suggest that the combination of Down's syndrome and the "intellectual disability and medical disorders" that can accompany Down's syndrome added to a possible higher rate of autism potentially make for "a severely disabled group" worthy of far greater attention when it comes to screening and intervention. I don't think anyone would disagree with such sentiments and in particular, how preferential autism screening should once again be added to a growing list of diagnoses and labels. Indeed, such data in particular directs further attention to the link between intellectual (learning) disability and autism (see here and see here).
 Oxelgren UW. et al. Prevalence of autism and attention-deficit-hyperactivity disorder in Down syndrome: a population-based study. Dev Med Child Neurol. 2016 Aug 9.
Oxelgren UW, Myrelid Å, Annerén G, Ekstam B, Göransson C, Holmbom A, Isaksson A, Åberg M, Gustafsson J, & Fernell E (2016). Prevalence of autism and attention-deficit-hyperactivity disorder in Down syndrome: a population-based study. Developmental medicine and child neurology PMID: 27503703