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

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Title: Autism among Adults with Down Syndrome: Prevalence, Medicaid Usage, and Co-Occurring Conditions
Language: English
Authors: Eric Rubenstein (ORCID 0000-0002-9146-4497), Mack Toth, Salina Tewolde
Source: Journal of Autism and Developmental Disorders. 2025 55(10):3670-3677.
Availability: Springer. Available from: Springer Nature. One New York Plaza, Suite 4600, New York, NY 10004. Tel: 800-777-4643; Tel: 212-460-1500; Fax: 212-460-1700; e-mail: customerservice@springernature.com; Web site: https://link.springer.com/
Peer Reviewed: Y
Page Count: 8
Publication Date: 2025
Sponsoring Agency: National Institute on Aging (NIA) (DHHS/NIH)
Contract Number: R01AG073179
Document Type: Journal Articles
Reports - Evaluative
Descriptors: Autism Spectrum Disorders, Down Syndrome, Adults, Comorbidity, Welfare Services, Health Insurance, Costs, Hospitals, Diseases, Physical Health, Mental Health, Incidence
DOI: 10.1007/s10803-024-06484-2
ISSN: 0162-3257
1573-3432
Abstract: 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.
Abstractor: As Provided
Entry Date: 2025
Accession Number: EJ1489248
Database: ERIC
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  Value: <anid>AN0188317766;aut01oct.25;2025Oct01.03:39;v2.2.500</anid> <title id="AN0188317766-1">Autism Among Adults with Down Syndrome: Prevalence, Medicaid Usage, and Co-Occurring Conditions </title> <p>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.</p> <p>Keywords: Down syndrome; Medicaid; Autism; Co-occurring conditions; Medical and Health Sciences Public Health and Health Services</p> <p>Copyright comment Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.</p> <p>Autism spectrum disorder (hereafter: autism) and Down syndrome are both relatively common developmental conditions that impact social emotional development. Autism is defined by impairment in social communication and repetitive and restricted behaviors and interests. It is present in an approximately 2% of US youth (Maenner et al., [<reflink idref="bib13" id="ref1">13</reflink>]). Autism is highly heritable, and is caused by a complex gene in environment interactions; although for many cases there is no specifically identified gene (Yasuda et al., [<reflink idref="bib26" id="ref2">26</reflink>]) Down syndrome is the most common genetic cause of intellectual disability, with prevalence of 1 in 800 live births (Bull, [<reflink idref="bib5" id="ref3">5</reflink>]). Consistently, studies show that autism is more likely to co-occur in young children with Down syndrome, compared to the prevalence in the non-Down syndrome population (Reilly, [<reflink idref="bib15" id="ref4">15</reflink>]), with an estimated 16% of children with Down syndrome being identified as autistic (Richards et al., [<reflink idref="bib16" id="ref5">16</reflink>]).</p> <p>Diagnosing autism in children with Down syndrome is challenging, as parents report over a 4-year gap from seeing signs of autism to receiving a diagnosis (Spinazzi et al., [<reflink idref="bib21" id="ref6">21</reflink>]). Delays are likely caused by a lack of provider knowledge on how autism presents in Down syndrome, diagnostic overshadowing (where clinician's assume the one diagnosis explains the whole phenotype), and potentially autism diagnostic measures not being adapted for a Down syndrome population (Reilly, [<reflink idref="bib15" id="ref7">15</reflink>]; Spinazzi et al., [<reflink idref="bib21" id="ref8">21</reflink>]). Patterns in autism diagnosis over time likely impacts the prevalence of co-occurrence between the two conditions. The first large cohorts with identified autism have recently entered adulthood (Rubenstein & Bishop, [<reflink idref="bib17" id="ref9">17</reflink>]), meaning that studies of adults with autism (or Down syndrome) were not able to detect a large proportion of the population who did not have diagnoses.</p> <p>While the evidence of increased co-occurrence is strong, there are still many unknowns about the overlap of the two conditions, especially in adulthood. Change in autism prevalence over time has been well documented (Autism Developmental Disabilities Monitoring Network Surveillance Year Principal Investigators et al., [<reflink idref="bib2" id="ref10">2</reflink>]; Maenner et al., [<reflink idref="bib13" id="ref11">13</reflink>]), and prevalence in adult populations is being explored, (Dietz et al., [<reflink idref="bib9" id="ref12">9</reflink>]; Rubenstein, Tewolde, Rubenstein et al., [<reflink idref="bib19" id="ref13">19</reflink>], [<reflink idref="bib20" id="ref14">20</reflink>]) but whether and to what extent that increase occurred in Down syndrome is not known. Further, healthcare use and spending are high for Down syndrome (Rubenstein, Michals, Rubenstein et al., [<reflink idref="bib19" id="ref15">19</reflink>], [<reflink idref="bib20" id="ref16">20</reflink>]) and autism (Ghanouni et al., [<reflink idref="bib10" id="ref17">10</reflink>]), and documenting service use and cost is important for allocating services and optimizing care- especially for programs like Medicaid that serve a sizeable portion of adults with autism and Down syndrome (Rubenstein & Bishop, [<reflink idref="bib17" id="ref18">17</reflink>]; Rubenstein, Michals, Rubenstein et al., [<reflink idref="bib19" id="ref19">19</reflink>], [<reflink idref="bib20" id="ref20">20</reflink>]; Rubenstein, Tewolde, Rubenstein et al., [<reflink idref="bib19" id="ref21">19</reflink>], [<reflink idref="bib20" id="ref22">20</reflink>]). Additionally, autism and Down syndrome each present with unique co-occurring conditions, but the constellation of conditions for Down syndrome and autism together is not clear (Rubenstein & Bishop, [<reflink idref="bib17" id="ref23">17</reflink>]). Spinazzi et al. ([<reflink idref="bib21" id="ref24">21</reflink>]) found children with Down syndrome and autism had greater odds of gastrointestinal issues and spasms compared to children with Down syndrome alone, but they were not able to compare to an autism group. There is less known about chronic conditions for this group with both conditions as they age into middle and older adulthood, where people with Down syndrome are at high risk of Alzheimer's dementia (Rubenstein et al., [<reflink idref="bib18" id="ref25">18</reflink>]), and people with autism have a bevy of cardiovascular and mental health issues (Bishop-Fitzpatrick & Rubenstein, [<reflink idref="bib4" id="ref26">4</reflink>]).</p> <p>With the increasing prevalence of autism and improved access to Medicaid data, which many individuals with Down syndrome and/or autism rely on for health insurance(Rubenstein et al., [<reflink idref="bib19" id="ref27">19</reflink>]), there is an opportunity to describe the population with Down syndrome alone, autism alone, and those with both conditions. Therefore, 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.</p> <hd id="AN0188317766-2">Methods</hd> <p></p> <hd id="AN0188317766-3">Data Source</hd> <p>Data was from the Down Syndrome Toward Optimal Trajectories and Health Equity using Medicaid Analytic eXtract project (DS-TO-THE-MAX). DS-TO-THE-MAX is a longitudinal claims database of 5,000,000 Medicaid enrollees of adults 18 years or older between 2011 and 2019. DS-TO-THE-MAX is a combination of two databases: Medicaid Analytic eXtract (MAX; 2011–2015) and the Transformed Medicaid Statistical Information System Analytic Files (TAF; 2014–2019). Between the years 2014 to 2015, there was a changeover period where some states remained using MAX while other states began using TAF. Accounting for this overlap, unique beneficiary identifiers were used to link the two databases. Most demographic variables followed the same format and were checked for consistency. Other variables were adjusted to synchronize across both systems. Further information is provided in (Citation removed for peer review).</p> <hd id="AN0188317766-4">Autism and Down Syndrome Identification</hd> <p>We used established algorithms that used ICD-9 and ICD-10 codes to identify autism and Down syndrome within administrative claims. This process is described in more detail elsewhere (Bishop-Fitzpatrick & Rubenstein, [<reflink idref="bib4" id="ref28">4</reflink>]; McDermott et al., [<reflink idref="bib14" id="ref29">14</reflink>]; Straub et al., [<reflink idref="bib24" id="ref30">24</reflink>]). Given this process, we had three study groups: Down syndrome alone, autism alone, and Down syndrome + autism. We excluded those that did not have either condition.</p> <hd id="AN0188317766-5">Demographic Data</hd> <p>Demographic data were from the demographic and person enrollment Medicaid files. Race and ethnicity were self-reported and harmonized across states by the Centers for Medicare and Medicaid services. To account for potential bias if restricting to those with just complete demographic data (Sterne et al., [<reflink idref="bib23" id="ref31">23</reflink>]), we used multiple imputation to account for missing race data (~ 12.5% missing) by using zip code level demographics and our data to probabilistically determine race/ethnicity We also examined age at study entry, region, whether one was qualified for Medicaid via disability or income, and years enrolled.</p> <hd id="AN0188317766-6">Claims & Service Use</hd> <p>Within Medicaid data, a claim or encounter is a documentation of billed health care service. We used the inpatient, other services, and long-term care files to count the claims per person per year. We examined hospitalization and long-term care days by looking for hospitalization claims and long-term care stays with nonoverlapping admission dates.</p> <hd id="AN0188317766-7">Cost</hd> <p>We used fee-for-service and capitated payments to determine an individual's cost per person year. The Medicaid paid amount is money the Medicaid system paid the provider and does not reflect the original billed amount or out-of-pocket expenses. Capitated payments accounted for managed care organization provided service.</p> <hd id="AN0188317766-8">Chronic Conditions</hd> <p>We used Center for Medicare and Medicaid Services Chronic Condition Warehouse algorithms to evaluate prevalence of specific co-occurring conditions relevant to Down syndrome and or autism in our nine years of data. Algorithms are validated and commonly used(Center for Medicare and Medicaid Services, [<reflink idref="bib7" id="ref32">7</reflink>], [<reflink idref="bib6" id="ref33">6</reflink>]). We examined conditions prevalent in both autism and Down syndrome separately (Bishop-Fitzpatrick & Rubenstein, [<reflink idref="bib4" id="ref34">4</reflink>]; Bull, [<reflink idref="bib5" id="ref35">5</reflink>]) obesity, kidney disease, epilepsy, hypertension, heart failure, diabetes, depression, dementia, and atrial fibrillation.</p> <hd id="AN0188317766-9">Statistical Analysis</hd> <p>We examined demographic characteristics by group (autism, Down syndrome, Down syndrome + autism). We calculated means and medians for service and cost outcomes and age standardized means using direct standardization with the autism group as the referent. We graphed percentage in each group by age over time. Then, we compared age-standardized death rates, claims per person-year, Medicaid costs per person-year, inpatient hospitalizations per person-year, and day in long-term care per person-year by group using Kruskal Wallis tests. We excluded costs <$0 (capitated payments) and long-term care days > 365 (double counting based on facility type) as outliers. We calculated proportion of individuals within each group that had each chronic condition and then ran log-Poisson models to calculate prevalence ratios. We ran an unadjusted model with a person-time offset to account for different enrollment lengths and then an adjusted model which included categorized age, sex, and region.</p> <hd id="AN0188317766-10">Results</hd> <p>Between 2011 and 2019, there were 519,450 adult Medicaid enrollees who met our criteria for autism (<emph>N</emph> = 396,426), Down syndrome (<emph>N</emph> = 116,422), or both Down syndrome and autism (<emph>N</emph> = 6,602) (Table 1). Among enrollees with just autism, 74.4% were male compared to 64.7% of those with Down syndrome and autism and 50.8% with just Down syndrome. Most enrollees identified as white (74% in each group) and non-Hispanic (87.9% in the autism group, 83.2% in the Down syndrome group and 85.3% in the Down syndrome + autism group). By US region, the south had the highest percentage of adults with Down syndrome, with or without autism.</p> <p>Table 1 Demographics of adults with Autism, Down syndrome, and Autism and Down syndromes claims Medicaid between 2011–2019</p> <p> <ephtml> <table frame="hsides" rules="groups"><thead><tr><th align="left" rowspan="2" /><th align="left"><p>Autism</p></th><th align="left"><p>Down Syndrome</p></th><th align="left"><p>Down Syndrome + Autism</p></th></tr><tr><th align="left"><p>N = 396,426</p></th><th align="left"><p>N = 116,422</p></th><th align="left"><p>N = 6,602</p></th></tr></thead><tbody><tr><td align="left"><p><italic>Sex</italic></p></td><td align="left"><p>N (%)</p></td><td align="left"><p>N (%)</p></td><td align="left"><p>N (%)</p></td></tr><tr><td align="left"><p>Male</p></td><td align="left"><p>295,031 (74.4%)</p></td><td align="left"><p>59,154 (50.8%)</p></td><td align="left"><p>4,270(64.7%)</p></td></tr><tr><td align="left"><p>Female</p></td><td align="left"><p>101,393 (25.6%)</p></td><td align="left"><p>57,268 (49.2%)</p></td><td align="left"><p>2,332 (35.3%)</p></td></tr><tr><td align="left"><p><italic>Race</italic></p></td><td align="left" /><td align="left" /><td align="left" /></tr><tr><td align="left"><p>White</p></td><td align="left"><p>283,042 (74.2%)</p></td><td align="left"><p>84,228 (74.7%)</p></td><td align="left"><p>4,737 (74.2%)</p></td></tr><tr><td align="left"><p>Black</p></td><td align="left"><p>64,017 (16.8%)</p></td><td align="left"><p>15,797 (14.0%)</p></td><td align="left"><p>1,029 (16.1%)</p></td></tr><tr><td align="left"><p>Pacific Islander</p></td><td align="left"><p>3,063 (0.8%)</p></td><td align="left"><p>1,193 (1.1%)</p></td><td align="left"><p>63 (1.0%)</p></td></tr><tr><td align="left"><p>Asian</p></td><td align="left"><p>12,515 (3.3%)</p></td><td align="left"><p>3,825 (3.4%)</p></td><td align="left"><p>204 (3.2%)</p></td></tr><tr><td align="left"><p>Native American</p></td><td align="left"><p>2,885 (0.8%)</p></td><td align="left"><p>1,005 (0.9%)</p></td><td align="left"><p>29 (0.45%)</p></td></tr><tr><td align="left"><p>Multiple Races</p></td><td align="left"><p>15,863 (4.2%)</p></td><td align="left"><p>6,762 (6.0%)</p></td><td align="left"><p>323 (5.1%)</p></td></tr><tr><td align="left"><p><italic>Ethnicity</italic></p></td><td align="left" /><td align="left" /><td align="left" /></tr><tr><td align="left"><p>Non-Hispanic/Latino</p></td><td align="left"><p>3,335,134 (87.9%)</p></td><td align="left"><p>93,874 (83.2%)</p></td><td align="left"><p>5,445 (85.3%)</p></td></tr><tr><td align="left"><p>Hispanic/Latino</p></td><td align="left"><p>46,251 (12.1%)</p></td><td align="left"><p>18,936 (16.8%)</p></td><td align="left"><p>940 (14.7%)</p></td></tr><tr><td align="left"><p><italic>Region</italic></p></td><td align="left" /><td align="left" /><td align="left" /></tr><tr><td align="left"><p>Northeast</p></td><td align="left"><p>109,534 (27.6%)</p></td><td align="left"><p>25,791 (22.2%)</p></td><td align="left"><p>1,645 (24.9%)</p></td></tr><tr><td align="left"><p>Midwest</p></td><td align="left"><p>93,316 (23.5%)</p></td><td align="left"><p>26,774 (23.0%)</p></td><td align="left"><p>1,311 (19.9%)</p></td></tr><tr><td align="left"><p>South</p></td><td align="left"><p>1,120,23 (28.3%)</p></td><td align="left"><p>37,507 (32.2%)</p></td><td align="left"><p>2,556 (38.7%)</p></td></tr><tr><td align="left"><p>West</p></td><td align="left"><p>80,336 (20.3%)</p></td><td align="left"><p>25,707 (22.1%)</p></td><td align="left"><p>1,075 (16.3%)</p></td></tr><tr><td align="left"><p><italic>Eligibility</italic></p></td><td align="left" /><td align="left" /><td align="left" /></tr><tr><td align="left"><p>Disability</p></td><td align="left"><p>231,901 (58.5%)</p></td><td align="left"><p>94,667 (81.3%)</p></td><td align="left"><p>4,877 (73.9%)</p></td></tr><tr><td align="left"><p>Income</p></td><td align="left"><p>250,129 (63.1%)</p></td><td align="left"><p>54,076 (46.5%)</p></td><td align="left"><p>308,095 (59.3%)</p></td></tr><tr><td align="left"><p>Dual</p></td><td align="left"><p>134,763 (34.0%)</p></td><td align="left"><p>69,983 (60.1%)</p></td><td align="left"><p>3,180 (48.8%)</p></td></tr><tr><td align="left"><p><italic>Age at study entry</italic></p></td><td align="left" /><td align="left" /><td align="left" /></tr><tr><td align="left"><p>18–25</p></td><td align="left"><p>276,976 (69.9%)</p></td><td align="left"><p>39,985 (34.3%)</p></td><td align="left"><p>3,935 (59.6%)</p></td></tr><tr><td align="left"><p>26–34</p></td><td align="left"><p>55,500 (14.0%)</p></td><td align="left"><p>20,166 (17.3%)</p></td><td align="left"><p>981 (14.9%)</p></td></tr><tr><td align="left"><p>35–44</p></td><td align="left"><p>27,563 (7.0%)</p></td><td align="left"><p>18,957 (16.3%)</p></td><td align="left"><p>701 (10.6%)</p></td></tr><tr><td align="left"><p>45–54</p></td><td align="left"><p>20,967 (5.3%)</p></td><td align="left"><p>22,630 (19.4%)</p></td><td align="left"><p>704 (10.7%)</p></td></tr><tr><td align="left"><p>55–64</p></td><td align="left"><p>11,397 (2.9%)</p></td><td align="left"><p>12,257 (10.5%)</p></td><td align="left"><p>246 (3.7%)</p></td></tr><tr><td align="left"><p>65–89</p></td><td align="left"><p>4,023 (1.0%)</p></td><td align="left"><p>2,427 (2.1%)</p></td><td align="left"><p>35 (0.5%)</p></td></tr><tr><td align="left"><p><italic>Person-years by age</italic></p></td><td align="left" /><td align="left" /><td align="left" /></tr><tr><td align="left"><p>18–25</p></td><td align="left"><p>1,113,734 (48.8%)</p></td><td align="left"><p>166,146 (21.4%)</p></td><td align="left"><p>17,452 (39.2%)</p></td></tr><tr><td align="left"><p>26–34</p></td><td align="left"><p>569,464 (25%)</p></td><td align="left"><p>162,460 (20.9%)</p></td><td align="left"><p>10,706 (24%)</p></td></tr><tr><td align="left"><p>35–44</p></td><td align="left"><p>254,702 (11.2%)</p></td><td align="left"><p>143,157 (18.4%)</p></td><td align="left"><p>6,241 (14%)</p></td></tr><tr><td align="left"><p>45–54</p></td><td align="left"><p>177,465 (7.8%)</p></td><td align="left"><p>165,448 (21.3%)</p></td><td align="left"><p>5,965 (13.4%)</p></td></tr><tr><td align="left"><p>55–64</p></td><td align="left"><p>115,792 (5.1%)</p></td><td align="left"><p>113,468 (14.6%)</p></td><td align="left"><p>3,524 (7.9%)</p></td></tr><tr><td align="left"><p>65–89</p></td><td align="left"><p>50,733 (2.2%)</p></td><td align="left"><p>25,871 (3.3%)</p></td><td align="left"><p>633 (1.4%)</p></td></tr><tr><td align="left"><p>Total PY</p></td><td align="left"><p>2,277,565</p></td><td align="left"><p>775,777</p></td><td align="left"><p>44,496</p></td></tr><tr><td align="left"><p>Deaths, Deaths per 1000 PY</p></td><td align="left"><p>8,446 (3.7)</p></td><td align="left"><p>19,629 (12.4)</p></td><td align="left"><p>465 (8.7)</p></td></tr></tbody></table> </ephtml> </p> <p>PY Person years Death rate age standardized with autism group as the referent</p> <hd id="AN0188317766-11">Medicaid Enrollment</hd> <p>Occurrence of autism and Down syndrome (Fig. 1) increased substantially from 2011 to 2019 (240% times the number with autism, 180% times the number with Down syndrome + autism). The number with Down syndrome was 8% higher in 2019 compared to 2011. In 2011, 4.1% of enrollees with Down syndrome (<emph>N</emph> = 3,392) had co-occurring autism; by 2011 it was 6.6% (<emph>N</emph> = 6,102). The increase was largest in the 18–25 age group, with a prevalence of 3.9% in 2011 and 8.7% in 2019. Prevalence in the other age groups was not meaningfully different.</p> <p>Graph: Fig. 1 Autism prevalence among adults with down syndrome in Medicaid, overall and by age group, 2011–2019</p> <hd id="AN0188317766-12">Medicaid Service Use & Cost</hd> <p>Without age adjustment, the autism group had the fewest claims, costs, inpatient hospitalization rate, followed by the Down syndrome group, then the Down syndrome + autism group (Table 2). After age adjustment, all measures in the Down syndrome group were reduced while the Down syndrome + autism grouped remained similar. All use and cost variables significantly differed by group based on the Kruskal Wallis test (all <emph>P</emph> < 0.001); however, after age adjustment the autism and Down syndrome groups were not meaningfully different.</p> <p>Table 2 Cost and service use for adults with autism, Down syndrome, or Down syndrome + autism enrolled in Medicaid, 2011–2019</p> <p> <ephtml> <table frame="hsides" rules="groups"><thead><tr><th align="left" rowspan="3" /><th align="left" colspan="3"><p>Autism</p></th><th align="left" colspan="3"><p>Down syndrome</p></th><th align="left" colspan="3"><p>Down syndrome + autism</p></th></tr><tr><th align="left" colspan="3"><p>N = 396,426; PY = 2,277,565</p></th><th align="left" colspan="3"><p>N = 116,422; PY = 775,777</p></th><th align="left" colspan="3"><p>N = 6,602; PY = 44,496</p></th></tr><tr><th align="left"><p>Mean</p></th><th align="left"><p>Median</p></th><th align="left"><p>SD</p></th><th align="left"><p>Mean</p></th><th align="left"><p>Median</p></th><th align="left"><p>SD</p></th><th align="left"><p>Mean</p></th><th align="left"><p>Median</p></th><th align="left"><p>SD</p></th></tr></thead><tbody><tr><td align="left"><p><bold>Claims per PY</bold></p></td><td align="left" /><td align="left" /><td align="left" /><td align="left" /><td align="left" /><td align="left" /><td align="left" /><td align="left" /><td align="left" /></tr><tr><td align="left"><p>Unadjusted</p></td><td align="left"><p>178.8</p></td><td align="left"><p>112.00</p></td><td align="left"><p>23.3</p></td><td align="left"><p>201.4</p></td><td align="left"><p>128.2</p></td><td align="left"><p>199.1</p></td><td align="left"><p>266</p></td><td align="left"><p>200.4</p></td><td align="left"><p>214.9</p></td></tr><tr><td align="left"><p>Adjusted</p></td><td align="left"><p>-</p></td><td align="left"><p>-</p></td><td align="left"><p>-</p></td><td align="left"><p>186.9</p></td><td align="left" /><td align="left" /><td align="left"><p>263.1</p></td><td align="left" /><td align="left" /></tr><tr><td align="left" colspan="4"><p><bold>Medicaid costs per person year ($)</bold></p></td><td align="left" /><td align="left" /><td align="left" /><td align="left" /><td align="left" /><td align="left" /></tr><tr><td align="left"><p>Unadjusted</p></td><td align="left"><p>38,021.0</p></td><td align="left"><p>16,678.0</p></td><td align="left"><p>54,680.0</p></td><td align="left"><p>41,054.0</p></td><td align="left"><p>27,127.0</p></td><td align="left"><p>46,103.0</p></td><td align="left"><p>55,481.4</p></td><td align="left"><p>41,330.0</p></td><td align="left"><p>53,236.4</p></td></tr><tr><td align="left"><p>Adjusted</p></td><td align="left"><p>-</p></td><td align="left"><p>-</p></td><td align="left"><p>-</p></td><td align="left"><p>32,696.7</p></td><td align="left" /><td align="left" /><td align="left"><p>52,977.6</p></td><td align="left" /><td align="left" /></tr><tr><td align="left" colspan="4"><p><bold>Inpatient hospitalizations per person year</bold></p></td><td align="left" /><td align="left" /><td align="left" /><td align="left" /><td align="left" /><td align="left" /></tr><tr><td align="left"><p>Unadjusted</p></td><td align="left"><p>0.16</p></td><td align="left"><p>0</p></td><td align="left"><p>0.6</p></td><td align="left"><p>0.20</p></td><td align="left"><p>0</p></td><td align="left"><p>0.30</p></td><td align="left"><p>0.23</p></td><td align="left"><p>0</p></td><td align="left"><p>0.7</p></td></tr><tr><td align="left"><p>Adjusted</p></td><td align="left"><p>-</p></td><td align="left"><p>-</p></td><td align="left"><p>-</p></td><td align="left"><p>0.15</p></td><td align="left" /><td align="left" /><td align="left"><p>0.21</p></td><td align="left" /><td align="left" /></tr><tr><td align="left" colspan="4"><p><bold>Days in long term care per person year</bold></p></td><td align="left" /><td align="left" /><td align="left" /><td align="left" /><td align="left" /><td align="left" /></tr><tr><td align="left"><p>Unadjusted</p></td><td align="left"><p>8.3</p></td><td align="left"><p>0.0</p></td><td align="left"><p>43.3</p></td><td align="left"><p>21.4</p></td><td align="left"><p>0</p></td><td align="left"><p>69.0</p></td><td align="left"><p>13.60</p></td><td align="left"><p>0</p></td><td align="left"><p>56.6</p></td></tr><tr><td align="left"><p>Adjusted</p></td><td align="left"><p>-</p></td><td align="left"><p>-</p></td><td align="left"><p>-</p></td><td align="left"><p>8.9</p></td><td align="left" /><td align="left" /><td align="left"><p>11.6</p></td><td align="left" /><td align="left" /></tr></tbody></table> </ephtml> </p> <p>SD standard deviation, PY person years Adjusted estimates standardized by age with the autism group being the referent We excluded negative costs and long-term care days > 365</p> <hd id="AN0188317766-13">Chronic Conditions</hd> <p>Conditions commonly occurred in all groups (Table 3). Among those with autism alone, 36% met depression criteria, compared to 20.5% of those with Down syndrome and 23.3% with Down syndrome + autism. Epilepsy was most common in the Down syndrome + autism group (24.2%). After adjustment for age, region, sex, and person-time (Fig. 2), those with Down syndrome alone and Down syndrome + autism had similar 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. Epilepsy was less common in the Down syndrome alone group compared to the autism alone group but the Down syndrome + autism group had 1.08 times the prevalence of epilepsy compared to the autism group.</p> <p>Table 3 Occurrence of chronic conditions in Medicaid claims among adults with autism, Down syndrome, and Down syndrome + autism, 2011–2019</p> <p> <ephtml> <table frame="hsides" rules="groups"><thead><tr><th align="left" rowspan="2"><p>Condition</p></th><th align="left" colspan="2"><p>Autism</p></th><th align="left" colspan="2"><p>Down syndrome</p></th><th align="left" colspan="2"><p>Down syndrome + autism</p></th></tr><tr><th align="left"><p>N = 396,426</p></th><th align="left"><p>%</p></th><th align="left"><p>N = 116,422</p></th><th align="left"><p>%</p></th><th align="left"><p>N = 6,602</p></th><th align="left"><p>%</p></th></tr></thead><tbody><tr><td align="left"><p>Atrial fibrillation</p></td><td align="left"><p>23,102</p></td><td align="left"><p>5.8</p></td><td align="left"><p>7,296</p></td><td align="left"><p>6.3</p></td><td align="left"><p>370</p></td><td align="left"><p>5.6</p></td></tr><tr><td align="left"><p>Dementia</p></td><td align="left"><p>16,220</p></td><td align="left"><p>4.1</p></td><td align="left"><p>23,970</p></td><td align="left"><p>20.6</p></td><td align="left"><p>911</p></td><td align="left"><p>13.8</p></td></tr><tr><td align="left"><p>Depression</p></td><td align="left"><p>142,710</p></td><td align="left"><p>36.0</p></td><td align="left"><p>23,895</p></td><td align="left"><p>20.5</p></td><td align="left"><p>1,534</p></td><td align="left"><p>23.2</p></td></tr><tr><td align="left"><p>Diabetes</p></td><td align="left"><p>44,395</p></td><td align="left"><p>11.2</p></td><td align="left"><p>21,685</p></td><td align="left"><p>18.6</p></td><td align="left"><p>1,114</p></td><td align="left"><p>16.9</p></td></tr><tr><td align="left"><p>Heart failure</p></td><td align="left"><p>9,905</p></td><td align="left"><p>2.5</p></td><td align="left"><p>15,321</p></td><td align="left"><p>13.2</p></td><td align="left"><p>637</p></td><td align="left"><p>9.7</p></td></tr><tr><td align="left"><p>Hypertension</p></td><td align="left"><p>77,421</p></td><td align="left"><p>19.5</p></td><td align="left"><p>29,817</p></td><td align="left"><p>25.6</p></td><td align="left"><p>1,571</p></td><td align="left"><p>23.8</p></td></tr><tr><td align="left"><p>Epilepsy</p></td><td align="left"><p>64,987</p></td><td align="left"><p>16.4</p></td><td align="left"><p>18,442</p></td><td align="left"><p>15.8</p></td><td align="left"><p>1,598</p></td><td align="left"><p>24.2</p></td></tr><tr><td align="left"><p>Kidney disease</p></td><td align="left"><p>37,949</p></td><td align="left"><p>9.6</p></td><td align="left"><p>26,959</p></td><td align="left"><p>23.2</p></td><td align="left"><p>1,423</p></td><td align="left"><p>21.6</p></td></tr><tr><td align="left"><p>Obesity</p></td><td align="left"><p>81,472</p></td><td align="left"><p>20.6</p></td><td align="left"><p>34,834</p></td><td align="left"><p>29.9</p></td><td align="left"><p>1,900</p></td><td align="left"><p>28.8</p></td></tr></tbody></table> </ephtml> </p> <p>Graph: Fig. 2 Prevalence rate ratios for common chronic conditions comparing down syndrome, autism, and down syndrome + autism in Medicaid enrolled adults, 2011–2019. DS: Down syndrome. ASD: autism spectrum disorder. Adjusted for age, sex, region, and person-time</p> <hd id="AN0188317766-14">Discussion</hd> <p>Autism and Down syndrome are developmental conditions that affect individuals differently across the lifespan. Because of increased identification in autism and improved survival in Down syndrome, there are now growing adult populations with these conditions and an underexplored population with both conditions. We used a large longitudinal Medicaid data set to document the increased occurrence, high healthcare use, and risk of chronic conditions of this group with Down syndrome + autism.</p> <p>Our estimate of the prevalence of autism, conditional on having Down syndrome, was 6.6% in 2019. Our estimate was considerably lower than the meta-synthesized estimate of 16% by Richards et al.(Richards et al., [<reflink idref="bib16" id="ref36">16</reflink>]). Autism prevalence is consistently lower in adults than children due to known diagnostic trends and lack of appropriate measures (Huang et al., [<reflink idref="bib12" id="ref37">12</reflink>]). Therefore, we are not surprised to see relatively lower estimates. Compared to autism prevalence in 2019, estimated using denominators of all enrolled in Medicaid (Rubenstein et al., [<reflink idref="bib20" id="ref38">20</reflink>]), autism prevalence among people with Down syndrome was 6.9 times the size (0.95% compared to 6.6%). There have been few studies documenting autism occurrence in adults with Down syndrome. Tasse et al., ([<reflink idref="bib25" id="ref39">25</reflink>]) conducted a survey of 291 adults with Down syndrome in Ohio and found 7.6% had autism diagnoses. In a UK sample 602 people with Down syndrome across the lifespan, 13.5% of adults 16–35 years and 2.5% of adults older than 35 had documented autism (Startin et al., [<reflink idref="bib22" id="ref40">22</reflink>]). We also saw decreasing occurrence with increasing age. Autism is more common among people with Down syndrome, but documentation of occurrence is affected by diagnostic trends in autism over time.</p> <p>For service use and cost, the Down syndrome + autism group had higher rates of service and costs than the Down syndrome alone and autism alone groups. Autism and Down syndrome have therapies and co-occurring conditions that lead individuals to rely on healthcare services (Bishop-Fitzpatrick & Rubenstein, [<reflink idref="bib4" id="ref41">4</reflink>]; Rubenstein et al., [<reflink idref="bib19" id="ref42">19</reflink>]), and we found that having both conditions leads to increased cost and use compared to having only one condition. Hospitalization rate and days of long-term care were higher in the Down syndrome + autism group compared to the other two groups. One reason for the increase may be that the phenotype of Down syndrome + autism is more severe than either alone. The Down syndrome + autism phenotype in children is marked by more deficits in communication and maladaptive behavior compared to autism alone or Down syndrome alone (Channell et al., [<reflink idref="bib8" id="ref43">8</reflink>]; Hamner et al., [<reflink idref="bib11" id="ref44">11</reflink>]). In adulthood this could result in more difficulty communicating with providers and lack of preventative care which can lead to more health service needs.</p> <p>Based on the chronic conditions we assessed, adults with Down syndrome + autism presented similarly to adults with Down syndrome. This may be the case because of the known and singular genetic origin of Down syndrome (triplication of chromosome 21). However, epilepsy in those with Down syndrome + autism was like the autism alone group. For example, autism is associated with conditions such as epilepsy (Bishop et al., [<reflink idref="bib3" id="ref45">3</reflink>]), that are not common in younger adults with Down syndrome (although they are more likely to develop epilepsy in older age) (Altuna et al., [<reflink idref="bib1" id="ref46">1</reflink>]) so it is not surprising that the Down syndrome + autism group had the highest occurrence. The occurrence of dementia was greater in the Down syndrome + autism group compared to the autism group after age adjustment. Signature plaques and tangles of Alzheimer's disease are evident in the brains of adults with Down syndrome by the age of 40 and upwards of 80% of adults with Down syndrome will have Alzheimer's disease.</p> <p>By relying on claims data, we were only able to examine documented autism, and cannot make inference about those with undiagnosed autism. Therefore, our population likely does not capture those with more subtle presentation. We assessed the Medicaid system and those that were dual enrolled in Medicare would have additional claims and costs that we would not see. Results and inferences should be placed in the context of the Medicaid system.</p> <p>Prevalence of autism is higher among people with Down syndrome than in peers and is increasing in recognition. By documenting occurrence in a full Medicaid population, we have illustrated the extent to which this population need care. With the combination of chronic conditions of autism and Down syndrome, namely epilepsy and dementia, those with Down syndrome + autism have a unique health profile that needs to be understood by providers. 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.</p> <hd id="AN0188317766-15">Funding</hd> <p>This work was funded by the National Institue on Aging grant R01AG073179.</p> <hd id="AN0188317766-16">Declarations</hd> <p></p> <hd id="AN0188317766-17">Conflicts of interests</hd> <p>The authors have no conflicts of interests to declare.</p> <hd id="AN0188317766-18">Publisher's Note</hd> <p>Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.</p> <ref id="AN0188317766-19"> <title> References </title> <blist> <bibl id="bib1" idref="ref46" type="bt">1</bibl> <bibtext> Altuna, M, Gimenez, S, & Fortea, J. (2021). Epilepsy in down syndrome: A highly prevalent comorbidity. 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  Data: Autism among Adults with Down Syndrome: Prevalence, Medicaid Usage, and Co-Occurring Conditions
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  Data: <searchLink fieldCode="AR" term="%22Eric+Rubenstein%22">Eric Rubenstein</searchLink> (ORCID <externalLink term="http://orcid.org/0000-0002-9146-4497">0000-0002-9146-4497</externalLink>)<br /><searchLink fieldCode="AR" term="%22Mack+Toth%22">Mack Toth</searchLink><br /><searchLink fieldCode="AR" term="%22Salina+Tewolde%22">Salina Tewolde</searchLink>
– Name: TitleSource
  Label: Source
  Group: Src
  Data: <searchLink fieldCode="SO" term="%22Journal+of+Autism+and+Developmental+Disorders%22"><i>Journal of Autism and Developmental Disorders</i></searchLink>. 2025 55(10):3670-3677.
– Name: Avail
  Label: Availability
  Group: Avail
  Data: Springer. Available from: Springer Nature. One New York Plaza, Suite 4600, New York, NY 10004. Tel: 800-777-4643; Tel: 212-460-1500; Fax: 212-460-1700; e-mail: customerservice@springernature.com; Web site: https://link.springer.com/
– Name: PeerReviewed
  Label: Peer Reviewed
  Group: SrcInfo
  Data: Y
– Name: Pages
  Label: Page Count
  Group: Src
  Data: 8
– Name: DatePubCY
  Label: Publication Date
  Group: Date
  Data: 2025
– Name: SourceSuprt
  Label: Sponsoring Agency
  Group: SrcSuprt
  Data: National Institute on Aging (NIA) (DHHS/NIH)
– Name: NumberContract
  Label: Contract Number
  Group: NumCntrct
  Data: R01AG073179
– Name: TypeDocument
  Label: Document Type
  Group: TypDoc
  Data: Journal Articles<br />Reports - Evaluative
– Name: Subject
  Label: Descriptors
  Group: Su
  Data: <searchLink fieldCode="DE" term="%22Autism+Spectrum+Disorders%22">Autism Spectrum Disorders</searchLink><br /><searchLink fieldCode="DE" term="%22Down+Syndrome%22">Down Syndrome</searchLink><br /><searchLink fieldCode="DE" term="%22Adults%22">Adults</searchLink><br /><searchLink fieldCode="DE" term="%22Comorbidity%22">Comorbidity</searchLink><br /><searchLink fieldCode="DE" term="%22Welfare+Services%22">Welfare Services</searchLink><br /><searchLink fieldCode="DE" term="%22Health+Insurance%22">Health Insurance</searchLink><br /><searchLink fieldCode="DE" term="%22Costs%22">Costs</searchLink><br /><searchLink fieldCode="DE" term="%22Hospitals%22">Hospitals</searchLink><br /><searchLink fieldCode="DE" term="%22Diseases%22">Diseases</searchLink><br /><searchLink fieldCode="DE" term="%22Physical+Health%22">Physical Health</searchLink><br /><searchLink fieldCode="DE" term="%22Mental+Health%22">Mental Health</searchLink><br /><searchLink fieldCode="DE" term="%22Incidence%22">Incidence</searchLink>
– Name: DOI
  Label: DOI
  Group: ID
  Data: 10.1007/s10803-024-06484-2
– Name: ISSN
  Label: ISSN
  Group: ISSN
  Data: 0162-3257<br />1573-3432
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: 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.
– Name: AbstractInfo
  Label: Abstractor
  Group: Ab
  Data: As Provided
– Name: DateEntry
  Label: Entry Date
  Group: Date
  Data: 2025
– Name: AN
  Label: Accession Number
  Group: ID
  Data: EJ1489248
PLink https://search.ebscohost.com/login.aspx?direct=true&site=eds-live&db=eric&AN=EJ1489248
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      – Type: doi
        Value: 10.1007/s10803-024-06484-2
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      – Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 8
        StartPage: 3670
    Subjects:
      – SubjectFull: Autism Spectrum Disorders
        Type: general
      – SubjectFull: Down Syndrome
        Type: general
      – SubjectFull: Adults
        Type: general
      – SubjectFull: Comorbidity
        Type: general
      – SubjectFull: Welfare Services
        Type: general
      – SubjectFull: Health Insurance
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      – SubjectFull: Costs
        Type: general
      – SubjectFull: Hospitals
        Type: general
      – SubjectFull: Diseases
        Type: general
      – SubjectFull: Physical Health
        Type: general
      – SubjectFull: Mental Health
        Type: general
      – SubjectFull: Incidence
        Type: general
    Titles:
      – TitleFull: Autism among Adults with Down Syndrome: Prevalence, Medicaid Usage, and Co-Occurring Conditions
        Type: main
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            NameFull: Eric Rubenstein
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            NameFull: Mack Toth
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            NameFull: Salina Tewolde
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            – D: 01
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              Type: published
              Y: 2025
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            – Type: issn-print
              Value: 0162-3257
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              Value: 1573-3432
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            – Type: volume
              Value: 55
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              Value: 10
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            – TitleFull: Journal of Autism and Developmental Disorders
              Type: main
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