Dementia Comes Early for People with Down Syndrome, and Is Often Missed

For people with Down syndrome, dementia usually arrives in their early fifties, far earlier than dementia typically begins in the general population, and by their sixties most are living with it. In a study of adults with Down syndrome in Barcelona and Cambridge, Alzheimer’s disease dementia was diagnosed at a median age of 53.7, and symptomatic Alzheimer’s disease reached 90–100% in people’s sixties^[1]. People with other learning disabilities also face a higher risk, and at younger ages.

Parents who have supported a son or daughter all their life, often growing old themselves, and long-standing support workers are frequently the first to notice small changes: a lost skill, a new hesitation on the stairs, a change in mood. Whether those changes are recognised as possible dementia, or put down to the learning disability, can decide whether support comes in time. This article sets out what research and official data from several countries show.

In Down syndrome, Alzheimer’s disease usually begins in the early fifties

Down syndrome is caused by an extra copy of chromosome 21, which carries the gene for amyloid precursor protein, and this places people with Down syndrome at high risk of Alzheimer’s disease^[5]. Researchers now describe Alzheimer’s disease associated with Down syndrome as a genetic form of dementia, and it is “now the leading cause of death in this population”^[6].

The timing is consistent across studies. A meta-analysis combining studies of 2,695 people with Down syndrome put the average age at onset of Alzheimer’s disease dementia at 53.8 years, the average age at death at 58.4, and the average time living with dementia at 4.6 years^[3]. In the Barcelona and Cambridge study of 388 adults with Down syndrome, brain changes measurable in spinal fluid and blood began as early as people’s twenties; prodromal (early symptomatic) Alzheimer’s disease was diagnosed at a median age of 50.2 and dementia at 53.7^[1].

Long-term cohorts show what this means across a lifetime. In Ireland, a study that followed 77 people with Down syndrome aged 35 and over from 1996 to 2015 found that 75 of them (97.4%) developed dementia, at a mean age of 55. Risk rose from 23% at age 50 to 80% at 65 and over, with no difference by level of intellectual disability^[7]. In Japan, a 2019 survey of 133 adults with Down syndrome in 45 welfare facilities found dementia in 34.6%, rising from none in their thirties to 65.5% in their sixties^[8].

These are high figures, but they are not a prediction for any one person. Age at diagnosis varies widely: in one English service, diagnoses ranged from age 36 to 73^[9]. Dementia that starts before 65 is covered more broadly in our study of young-onset dementia.

Recorded diagnoses fall well short of what cohort studies predict

Health records find less dementia than research cohorts, which suggests missed diagnoses. In California, an analysis of 2015 Medicare claims identified 878 people with Down syndrome aged 45 and over; 353 of them (40%) had a recorded dementia diagnosis, rising to 49% among those aged 65 and over^[5]. In Germany, health insurance claims from 2010 to 2019 showed recorded dementia in an average of 9.2% of adults with Down syndrome, against 3.2% of adults without. At ages 56 to 60 the figures were 28.7% and 0.7%^[10]. The German authors conclude that although recorded prevalence is far higher than in the general population, it is lower than epidemiological studies would predict, which “suggests a potential underdiagnosis of dementia” among people with Down syndrome^[10].

Death records show the same gap. A study of 77,347 US death certificates mentioning Down syndrome between 1968 and 2019 found that the pattern of ages at death matched what would be expected if Alzheimer’s disease were fully penetrant in up to 80% of deaths, yet dementia was mentioned on only 30% of certificates. In the Barcelona cohort, where people were followed closely, the figure was 78.9%^[3]. On US death certificates coded for Down syndrome, median age at death rose from 1 year in 1968 to 57 in 2019, a period in which death certification practice also changed^[3]. The authors conclude that lifespan “will not increase until disease-modifying treatments for Alzheimer disease are available”^[3].

Other people with a learning disability also face higher risk, and earlier

In England, a study followed 222 people aged 60 and over with an intellectual disability but not Down syndrome. Of the 134 who did not have dementia at the start and were still alive at follow-up, 21 (15.7%) had developed it. Among those aged 65 and over, the rate of new cases was about five times that expected in the general population (standardised incidence ratio 4.98)^[11].

A national registry study in Korea, which followed people aged 40 and over from 2009 to 2020, found an adjusted hazard ratio of 5.75 for all-cause dementia in people with an intellectual disability compared with those without. The raised risk was especially marked at ages 40 to 64^[4]. In Japan, a survey of 1,831 adults with an intellectual disability (not Down syndrome) living in facilities found dementia in 8.8% of those aged 60 to 64, rising to 19.6% at 70 to 74^[12].

The Japanese study found hypertension, depression, stroke and traumatic brain injury associated with dementia; the authors suggest that treating hypertension and depression and preventing head injury and stroke may reduce risk^[12]. These are associations in cross-sectional data, not proof of cause. Wider health in later life for people with a learning disability, including health checks and multimorbidity, is covered in our study of older people with a learning disability.

Dementia is the most common recorded cause of death among adults with Down syndrome whose deaths were reviewed in England

England’s Learning from Lives and Deaths programme (LeDeR) reviews the deaths of people with a learning disability. Its report for 2024 analysed 1,986 adults with Down syndrome and 9,701 other adults with a learning disability who died between January 2021 and December 2024^[2]. Dementia was recorded for 39.8% of the adults with Down syndrome, against 5.1% of other adults with a learning disability. The most common underlying causes of death among adults with Down syndrome were unspecified dementia (17.3%) and early-onset Alzheimer’s disease (10.0%)^[2].

Deaths came early. More than three-quarters (78.8%) of adults with Down syndrome died before 65, compared with 52.4% of other adults with a learning disability, and their median age at death was 59.8 years, against 64.1 for other adults with a learning disability and 81.9 for the general adult population of England and Wales in 2022^[2]. Adults with Down syndrome were also more likely to die in a residential or nursing home (23.8% against 15.4%)^[2].

Research cohorts point the same way. In a London study of 211 adults with Down syndrome aged 36 and over, 27 people died during follow-up at a mean age of 56.7, and 70% of them had dementia. Crude death rates among those with dementia were five times those of people without^[13]. In a Surrey learning disability service, just under 80% of people with Down syndrome diagnosed with dementia had died, with a median survival of four years after diagnosis; it was five years for people diagnosed in their forties and one year for those over 70^[9]. Care in the later stages is covered in our study of dementia and end-of-life care.

Diagnosis depends on knowing the person’s baseline, and baselines are often missing

For a person with a learning disability, the question is not how they score on a memory test, but how they have changed from their own usual level. An international consensus summit noted that many people with an intellectual disability already need help with daily activities “totally unrelated to dementia”, and agreed it is imperative that change “is measured from the person’s prior functioning”^[14]. A leading review notes that symptoms of dementia in people with Down syndrome “are overshadowed by the intellectual disability”, and that validated diagnostic criteria are lacking^[6].

This is the problem known as diagnostic overshadowing. NICE guidance in England defines it as “the tendency to attribute all behavioural, emotional, physical and social issues to a person’s learning disability or a pre-existing condition”, and asks practitioners, when needs change, not to assume the change is due to the learning disability^[15]. NICE’s dementia guideline asks that assessment scales take account of learning disabilities and communication difficulties that could affect results^[16].

A baseline assessment, made while the person is well, gives clinicians something to measure change against. British professional guidance cited in one recent study says a first assessment should take place around age 30–35. Yet in that Surrey service, covering 1993 to 2021, the average age at first assessment was around 49, and people assessed earlier were diagnosed earlier^[9]. In London, people living with family were diagnosed significantly earlier than others (hazard ratio 2.14), and the authors raise questions about undiagnosed dementia among people who died without a diagnosis^[13].

Screening tools help but are not enough on their own. In the US, an evaluation of the National Task Group Early Detection Screen for Dementia in 185 adults with Down syndrome found it useful, but that its findings need supplementing with other information to reach acceptable accuracy^[17]. Its consensus recommendations note that most physicians feel ill-prepared to evaluate suspected dementia in adults with intellectual disabilities^[18].

Treatable conditions, unready services and new drugs that do not yet reach this group

Dementia in Down syndrome rarely comes alone. In the California Medicare data, people with Down syndrome and dementia had more other conditions on average than those without (3.4 against 2.5), and four treatable conditions, hypothyroidism, epilepsy, anaemia and weight loss, were much more frequent in those with dementia^[5]. The authors call for more standardised follow-up to support better management of these conditions alongside dementia care^[5]. In England’s LeDeR reviews, treatable epilepsy accounted for 19.2% of avoidable deaths among adults with Down syndrome, against 8.0% among other adults with a learning disability^[2].

People working in and around services describe the gaps directly. In 14 interviews with professionals, patient representatives and care staff in Germany, lack of knowledge and experience among medical providers was the key challenge, with diagnosis hampered by a lack of suitable tools, time and money; interviewees also discussed increased use of sedatives^[19]. In an Australian qualitative study, families knew of the link between Down syndrome and Alzheimer’s disease but “lacked confidence in current dementia diagnostic pathways and worried about the future”^[20].

New treatments widen the gap. Anti-amyloid antibodies have been licensed in some countries for early Alzheimer’s disease, but current use recommendations exclude people with Down syndrome, partly because amyloid deposits in blood vessel walls are more common and side-effect risks are likely to be higher^[21]. Researchers describe adults with Down syndrome as potentially an optimal population for Alzheimer’s prevention trials, yet “there are no treatments to prevent Alzheimer’s disease”^[6]. For the wider picture, see our study of new dementia treatments.

What the evidence asks of us

The evidence is unusually clear about who is at risk and when, which makes the gaps in diagnosis and support harder to justify.

• Plan for dementia as part of ageing with Down syndrome. With dementia typically diagnosed in the early fifties, adult services need dementia pathways in place well before then^[1]. NICE asks that people with learning disabilities, particularly people with Down syndrome, and their families are told at an early stage about the link with dementia, the signs to look for and the support available^[15].
• Make baseline assessment routine, and on time. Professional guidance points to a first assessment around 30–35, yet one English service found the average first assessment came at about 49^[9]. Early baselines let later change be measured against the person’s own usual level, as international consensus recommends^[14].
• Treat change as a reason to look, not an expected part of the disability. Training on diagnostic overshadowing, and on treatable conditions such as thyroid problems and epilepsy, can help staff avoid missing either dementia or something else^[15][5].
• Open mainstream dementia services to people with a learning disability. NICE asks commissioners to ensure access to mainstream older people’s mental health services, including dementia support, and to provide families and carers with information, training and access to short breaks^[15].
• Count people properly. Claims data in the US and Germany and US death certificates all record less dementia than cohort studies predict^[5][10][3]. Reporting dementia diagnoses for people with a learning disability separately in national statistics would show whether diagnosis and support are reaching them.
• Include people with Down syndrome in treatment research. Current recommendations for anti-amyloid drugs exclude people with Down syndrome, and researchers call for further work so that they can be treated safely^[21].

For the wider library, see the Dementia & Health research hub.

Language: this piece uses person-first language ("people living with dementia", "people with dementia"), as most dementia organisations and people with lived experience prefer, and uses clinical terms such as "Alzheimer's disease" or "mild cognitive impairment" only where a study, dataset or diagnosis refers to that specific condition.

Why we're publishing this

People with a learning disability, and especially people with Down syndrome, are among those most likely to develop dementia, and among those least likely to have it recognised in time. Organisations that support them need clear, cited evidence to argue for earlier assessment, better-prepared services and a fair share of new treatments. We bring that evidence together so that dementia charities, learning disability organisations and families can use it.

How to read this data

The figures here come from very different kinds of source, and they measure different things. Research cohorts follow people closely with specialist assessment, so they find more dementia than routine records, but they are often small and may not represent everyone with Down syndrome. Claims data (California, Germany) and death certificates (US) count only recorded diagnoses, which the authors themselves judge to be incomplete. The Japanese studies surveyed people living in facilities, who may have higher support needs than others. LeDeR covers only deaths that were notified and reviewed.

Ratios are reported as each study measured them: the Korean figures are hazard ratios, adjusted for other factors; the English incidence figure is a standardised incidence ratio against general population rates. Risk factors are associations, not proof of cause. Almost all the evidence here comes from high-income countries; we did not find comparable data from low- and middle-income countries. “Learning disability” (the UK term) and “intellectual disability” (the international term) are used as each source uses them.

Use this data

Free to cite with attribution to Understanding Aging. Charities, carers' groups, campaigners and journalists are welcome to reuse these figures and charts. For the underlying figures as a spreadsheet, get in touch.

Important: This article summarises published research and statistics for general information. It is not medical, care or financial advice and cannot be used to diagnose, treat or predict anything about an individual. If you have concerns about your own or someone else's memory or health, please speak to a GP or another qualified health professional.

Sources

1. Fortea J, Vilaplana E, Carmona-Iragui M, et al. Clinical and biomarker changes of Alzheimer’s disease in adults with Down syndrome: a cross-sectional study. The Lancet, 2020. europepmc.org/article/MED/32593336
2. Yu MKL, Ditzel N, Bokor L, Sheehan R, Magill N, Ding J, Keagan-Bull R, Chauhan U, Tuffrey-Wijne I, Strydom A. Learning from Lives and Deaths: People with a learning disability and autistic people (LeDeR) report for 2024. King’s College London, 2026. kcl.ac.uk/ioppn/leder/leder2024
3. Iulita MF, Garzón Chavez D, Klitgaard Christensen M, et al. Association of Alzheimer disease with life expectancy in people with Down syndrome. JAMA Network Open, 2022. europepmc.org/article/MED/35604690
4. Um YJ, Cho IY, Koo HY, Park YM, Kim KM, Lee CE, Han K. Intellectual disabilities and risk of dementia: a Korean population-based cohort study. Journal of Intellectual Disabilities, 2026. europepmc.org/article/MED/42576197
5. Bayen E, Possin KL, Chen Y, Cleret de Langavant L, Yaffe K. Prevalence of aging, dementia, and multimorbidity in older adults with Down syndrome. JAMA Neurology, 2018. europepmc.org/article/MED/30032260
6. Fortea J, Zaman SH, Hartley S, Rafii MS, Head E, Carmona-Iragui M. Alzheimer’s disease associated with Down syndrome: a genetic form of dementia. The Lancet Neurology, 2021. europepmc.org/article/MED/34687637
7. McCarron M, McCallion P, Reilly E, Dunne P, Carroll R, Mulryan N. A prospective 20-year longitudinal follow-up of dementia in persons with Down syndrome. Journal of Intellectual Disability Research, 2017. europepmc.org/article/MED/28664561
8. Takenoshita S, Terada S, Inoue T, Kurozumi T, Takaki M, Kuwano R, Suemitsu S. Prevalence and modifiable risk factors of dementia in people with Down syndrome: cross-sectional study of Japan (INDIGO-2019). Journal of Intellectual Disability Research, 2026. europepmc.org/article/MED/41437814
9. Pounds O, Theodore K, Dodd K. Factors associated with Alzheimer’s dementia diagnosis and survival in Down syndrome. Journal of Intellectual Disability Research, 2025. europepmc.org/article/PMC/PMC12051232
10. Weitzel M, Walendzik A, Giebel GD, et al. (Alzheimer’s) dementia in adults with Down syndrome in Germany: administrative prevalence based on a claims data analysis. Journal of Alzheimer’s Disease, 2026. europepmc.org/article/MED/42138642
11. Strydom A, Chan T, King M, Hassiotis A, Livingston G. Incidence of dementia in older adults with intellectual disabilities. Research in Developmental Disabilities, 2013. europepmc.org/article/MED/23578903
12. Takenoshita S, Terada S, Inoue T, Kurozumi T, Yamada N, Kuwano R, Suemitsu S. Prevalence and modifiable risk factors for dementia in persons with intellectual disabilities. Alzheimer’s Research & Therapy, 2023. europepmc.org/article/MED/37464412
13. Hithersay R, Startin CM, Hamburg S, et al. Association of dementia with mortality among adults with Down syndrome older than 35 years. JAMA Neurology, 2019. europepmc.org/article/MED/30452522
14. McCarron M, McCallion P, Coppus A, et al. Supporting advanced dementia in people with Down syndrome and other intellectual disability: consensus statement of the International Summit on Intellectual Disability and Dementia. Journal of Intellectual Disability Research, 2018. europepmc.org/article/MED/29781149
15. National Institute for Health and Care Excellence. Care and support of people growing older with learning disabilities (NG96). NICE, 2018. nice.org.uk/guidance/ng96/chapter/Recommendations
16. National Institute for Health and Care Excellence. Dementia: assessment, management and support for people living with dementia and their carers (NG97). NICE, 2018. nice.org.uk/guidance/ng97/chapter/Recommendations
17. Silverman W, Krinsky-McHale SJ, Lai F, et al. Evaluation of the National Task Group-Early Detection Screen for Dementia: sensitivity to ‘mild cognitive impairment’ in adults with Down syndrome. Journal of Applied Research in Intellectual Disabilities, 2021. europepmc.org/article/MED/33314467
18. Moran JA, Rafii MS, Keller SM, Singh BK, Janicki MP. The National Task Group on Intellectual Disabilities and Dementia Practices consensus recommendations for the evaluation and management of dementia in adults with intellectual disabilities. Mayo Clinic Proceedings, 2013. europepmc.org/article/MED/23849993
19. Hüer T, Weitzel M, Giebel GD, et al. Alzheimer’s dementia in people with Down syndrome: results of guideline-assisted expert interviews on healthcare deficits in the diagnostics and treatment as well as solution approaches. Zeitschrift für Gerontologie und Geriatrie, 2025. europepmc.org/article/MED/39384617
20. Healy ML, Brodtmann A, Foster AM, Ayton D. Down syndrome and Alzheimer’s disease: a qualitative study exploring understanding and perceptions of dementia and diagnostic pathways among people with Down syndrome and their families. Journal of Intellectual Disability Research, 2026. europepmc.org/article/MED/42725843
21. Farrell C, Saini F, Beidas MM, Ryan NS, Strydom A, Wiseman FK. Use of anti-amyloid-β monoclonal antibodies in persons with Down syndrome Alzheimer’s disease. Alzheimer’s & Dementia, 2026. europepmc.org/article/MED/42043831