Autism Among Adults with Down Syndrome: Prevalence, Medicaid Usage, and Co-Occurring Conditions.

Our objective was to examine occurrence of both conditions in Medicaid; and compare Medicaid service use and cost, and chronic conditions among adults with Down syndrome and autism to those with Down syndrome alone and those with autism alone. We used ICD9 and ICD10 codes in Medicaid claims and encounters from 2011 to 2019 to identify autism and Down syndrome in adults > 18 years. We then calculated costs, claims, hospitalizations, long term care days, and chronic conditions, and compared by group- autism alone, Down syndrome alone, Down syndrome + autism. Between 2011 and 2019, there were 519,450 adult Medicaid enrollees who met our criteria for autism (N = 396,426), Down syndrome (N = 116,422), or both Down syndrome and autism (N = 6,602). In 2011, 4.1% of enrollees with Down syndrome had co-occurring autism; by 2011 it was 6.6%. The autism group had the fewest claims and inpatient hospitalizations, followed by the Down syndrome group, then the Down syndrome + autism group. After age adjustment, those with Down syndrome alone and Down syndrome + autism had elevated prevalence of atrial fibrillation, dementia, heart failure, kidney disease, and obesity compared to the autism alone group. Both groups also had decreased occurrence of depression and hypertension compared to the autism alone group. Prevalence of autism is higher among people with Down syndrome than in peers. The increased costs and service use for those with both conditions highlight the extent to which this population need health care and signal the need for more effective preventative care and therapies.