The earliest signs of dementia in someone with Down syndrome are often not what most people expect. Unlike typical Alzheimer’s disease, where forgetting names and misplacing objects tend to come first, dementia in people with Down syndrome usually announces itself through behavioral and personality changes — a withdrawal from social activities, a loss of enthusiasm for things the person once enjoyed, or a new pattern of irritability and anxiety. A family member might notice, for example, that their 45-year-old brother with Down syndrome who always loved his Thursday bowling league suddenly refuses to go, seems uncharacteristically apathetic, and has become fearful in situations that never bothered him before. These shifts can precede measurable memory loss by months or even years.
This pattern matters enormously because people with Down syndrome carry the single highest known risk factor for early-onset Alzheimer’s disease. The extra copy of chromosome 21 — the genetic basis of Down syndrome — includes the APP gene, which codes for amyloid precursor protein. That third copy leads to a lifelong overproduction of beta-amyloid, the protein that forms the toxic plaques found in Alzheimer’s brains. By age 40, nearly all people with Down syndrome have amyloid plaques and tau tangles in their brains, according to the Alzheimer’s Association, though most will not show clinical symptoms for another decade or more. This article walks through the specific warning signs caregivers and families should watch for, explains why dementia presents differently in this population, covers the diagnostic challenges that make early detection difficult, and outlines what steps families can take now — even before any symptoms appear — to improve outcomes.
Table of Contents
- Why Do the Signs of Dementia in Down Syndrome Look Different from Typical Alzheimer’s?
- The Specific Behavioral and Cognitive Warning Signs to Watch For
- Why People with Down Syndrome Face Such Elevated Alzheimer’s Risk
- How to Get an Accurate Diagnosis When Baseline Abilities Already Vary
- Why Dementia Progresses Faster in Down Syndrome and What That Means for Families
- The Role of Baseline Assessments Starting in the 30s
- Emerging Research and the Road Ahead
- Conclusion
- Frequently Asked Questions
Why Do the Signs of Dementia in Down Syndrome Look Different from Typical Alzheimer’s?
In the general population, Alzheimer’s disease typically begins with episodic memory problems — forgetting a recent conversation, asking the same question repeatedly, losing track of appointments. But in people with Down syndrome, the disease often follows what clinicians describe as a “frontal-like” dementia pattern. The frontal lobes of the brain govern personality, motivation, planning, and social behavior, and when these areas are affected early, the result is a person who seems to change in temperament and drive before they show obvious memory deficits. A 2025 study published in the Alzheimer’s & Dementia journal confirmed that agitation, depression, anxiety, apathy, and irritability were at least twice as prevalent in individuals with Down syndrome who had mild cognitive impairment compared to those with stable cognition, reinforcing that these behavioral shifts are genuine early markers rather than incidental changes. This distinction creates a real problem for families. When a parent notices their adult child with Down syndrome becoming unusually sad or uncooperative, the first assumption is rarely dementia.
They might attribute it to a change in routine, a new medication, a difficult transition at a day program, or simply “a phase.” And sometimes those explanations are correct. But when the behavioral change is persistent, progressive, and not explained by environmental factors, it deserves clinical attention. The frontal-like presentation also means that standard dementia screening tools designed for the general population — which lean heavily on memory testing — may miss what is happening entirely. It is also worth noting that not every person with Down syndrome will follow this frontal-dominant pattern. Some do present with memory loss as the leading symptom. The point is that families and clinicians who are only watching for memory problems will miss a substantial number of early cases.
The Specific Behavioral and Cognitive Warning Signs to Watch For
The British Psychological Society published updated guidance in 2025 outlining what early dementia looks like in people with Down syndrome, and the checklist is broader than many caregivers realize. Decline in executive function — the ability to plan, initiate tasks, solve problems, and follow multi-step routines — is one of the earliest and most consistent findings. A person who once independently packed their lunch and got ready for work might begin standing in the kitchen, unsure what to do next. They may struggle with tasks they previously handled, not because they have forgotten what a lunchbox is, but because the sequencing and initiative required to complete the routine has eroded. Alongside executive function decline, reduced interest in socializing and conversing is among the most commonly reported early signs, according to the Alzheimer’s Society UK. This can look like a person who used to greet housemates warmly now sitting silently at meals, or someone who always had opinions about what to watch on television becoming passive and indifferent.
Decreased enthusiasm for favored activities, sadness, fearfulness, and anxiety round out the emotional and motivational changes. Some individuals develop new sleep disturbances or restlessness. Others show irritability, uncooperativeness, or outright aggression that is out of character. However, one sign that should always prompt urgent medical evaluation is new-onset seizures in adulthood. While seizures can occur in people with Down syndrome for various reasons, their appearance for the first time in a person’s 40s or 50s is strongly associated with Alzheimer’s-related neurodegeneration. Changes in coordination, walking, and gait also belong on the radar. If a family notices their loved one shuffling, tripping more frequently, or struggling with balance in ways that are new, this warrants documentation and medical follow-up — not dismissal as “getting older.”.
Why People with Down Syndrome Face Such Elevated Alzheimer’s Risk
The biological explanation begins with trisomy 21 itself. Every cell in the body of a person with Down syndrome carries three copies of chromosome 21 instead of the usual two. Chromosome 21 happens to contain the APP gene, which provides the instructions for making amyloid precursor protein. With an extra copy of this gene running from birth, people with Down syndrome produce roughly 50 percent more amyloid precursor protein throughout their lives, leading to an accelerated buildup of beta-amyloid — the protein fragment that clumps into the plaques characteristic of Alzheimer’s disease. But APP is not the whole story. Research has identified additional chromosome 21 genes that contribute to the Alzheimer’s pathway. DYRK1A, for instance, is a kinase enzyme that phosphorylates APP in ways that increase the production of Abeta-42, a particularly neurotoxic form of the amyloid peptide.
This means the extra chromosome does not just produce more amyloid — it shifts the balance toward more dangerous forms of it. The combined effect is staggering: people with Down syndrome have a greater than 90 percent lifetime risk of developing Alzheimer’s disease, according to the National Institute on Aging. Roughly 30 percent of individuals in their 50s and approximately 50 percent in their 60s have clinically diagnosable Alzheimer’s dementia, per the National Down Syndrome Society. A 2024 study in JAMA Network Open found the mean age of dementia diagnosis was around 53.8 years, ranging from 51.4 years in the UK to 55.6 years in France. For families, these numbers can feel overwhelming. But an important counterpoint from the NDSS deserves emphasis: Alzheimer’s is not inevitable. While all people with Down syndrome are at elevated risk, and while nearly all will develop the brain pathology, many will not progress to clinical dementia in their lifetime. The distinction between having amyloid plaques in the brain and having dementia is real and significant.
How to Get an Accurate Diagnosis When Baseline Abilities Already Vary
Diagnosing dementia in someone with Down syndrome is genuinely more difficult than in the general population, and families should understand why. Most people with Down syndrome have some degree of baseline short-term memory difficulty and intellectual disability, which means the starting point is different for every individual. A clinician who does not know the person’s baseline level of functioning may not recognize that a decline has occurred, because the current performance might still fall within what they consider “expected” for someone with an intellectual disability. This is one of the most common reasons early dementia gets missed. The Alzheimer’s Association emphasizes that before attributing changes to dementia, clinicians must rule out other conditions that can mimic cognitive decline: thyroid problems, depression, chronic ear or sinus infections, vision loss, and sleep apnea are all more common in people with Down syndrome and can all cause behavioral and cognitive changes that look like dementia but are treatable. A thorough medical workup is not optional — it is the difference between a correct diagnosis and years of mislabeled decline.
For screening, the NTG-EDSD (National Task Group – Early Detection Screen for Dementia) is the recommended tool for this population. It is completed by a caregiver or informant who knows the person well, rather than relying on the individual to self-report symptoms. Two or more areas of concern on the NTG-EDSD suggest mild cognitive impairment, while three to five or more concerns indicate progression toward dementia. The tradeoff here is that the tool depends entirely on the quality of the informant’s observations. A caregiver who sees the person daily may notice subtle shifts that a quarterly medical appointment would miss, while a new or rotating staff member at a group home may lack the historical context to identify what has changed. This is why baseline assessments — ideally beginning in a person’s 30s — are so critical. Without a documented baseline, you are asking clinicians to detect a decline from a starting point no one recorded.
Why Dementia Progresses Faster in Down Syndrome and What That Means for Families
Research from Washington University School of Medicine has confirmed what many families observe firsthand: Alzheimer’s disease progresses faster in people with Down syndrome compared to the general population. The interval between early symptoms and significant functional decline tends to be compressed, which means the window for intervention and planning is shorter. A person in the general population might live with mild Alzheimer’s symptoms for several years before needing substantial care changes. For someone with Down syndrome, that trajectory can move more quickly, and families who delay evaluation or planning may find themselves managing a crisis rather than implementing a gradual care transition. This accelerated progression also has implications for clinical trials and treatment. Many emerging Alzheimer’s therapies are being studied in the Down syndrome population precisely because the biological pathway is so clearly understood, and because the predictable timeline makes it possible to measure treatment effects.
However, families should be cautious about assuming that treatments approved for typical Alzheimer’s will automatically work the same way in Down syndrome-related Alzheimer’s. The underlying biology overlaps but is not identical, and the presence of lifelong intellectual disability adds complexity to outcome measurement. Any treatment decisions should involve a clinician experienced with both Down syndrome and dementia. The emotional reality for families also deserves acknowledgment. Many parents of adults with Down syndrome are themselves aging, and confronting their child’s dementia while managing their own health challenges is extraordinarily difficult. Siblings who step into caregiving roles may not have the same deep familiarity with the person’s baseline behaviors. Building a care team early, documenting the person’s abilities and preferences while they are stable, and connecting with Down syndrome-specific Alzheimer’s support resources are not luxuries — they are necessities.
The Role of Baseline Assessments Starting in the 30s
The single most actionable recommendation from every major organization working at the intersection of Down syndrome and Alzheimer’s is this: establish a cognitive and functional baseline for every person with Down syndrome starting in their 30s. This means conducting a comprehensive assessment of memory, language, daily living skills, behavior, social engagement, and physical function while the person is healthy and stable, then repeating that assessment annually or biannually. When changes eventually appear, clinicians can compare current performance against the individual’s own documented history rather than guessing. Consider the difference in practice.
Without a baseline, a clinician sees a 48-year-old with Down syndrome who cannot remember what she had for breakfast and struggles to button her coat. Is that new? Has she always needed help with buttons? Did she used to recall meals? No one is sure. With a baseline recorded at ages 32, 35, and 38, the same clinician can see that she independently dressed herself and accurately described her daily activities at every prior assessment. The decline is unmistakable. Families can request baseline assessments through their loved one’s primary care provider, a neuropsychologist experienced with intellectual disability, or through specialty clinics affiliated with university centers on disabilities.
Emerging Research and the Road Ahead
The Down syndrome population has become one of the most important groups in Alzheimer’s research, and for a reason that is both tragic and scientifically valuable: the biological mechanism is clear, the timeline is relatively predictable, and the population is large enough to power meaningful studies. Ongoing research into the role of DYRK1A and other chromosome 21 genes beyond APP is opening new potential treatment targets. Blood-based biomarker tests that can detect Alzheimer’s pathology years before clinical symptoms are being validated specifically in people with Down syndrome, which could eventually allow for intervention at the earliest possible stage.
The 2025 finding that neuropsychiatric symptoms like agitation and apathy are reliable early markers of cognitive decline also points toward better screening protocols. If behavioral assessments can flag individuals who are transitioning from stable cognition to mild cognitive impairment, families and clinicians gain precious lead time. That time can be used for care planning, legal and financial preparation, medication trials, and — perhaps most importantly — ensuring the person with Down syndrome has a voice in decisions about their own future while they are still able to express their preferences.
Conclusion
The signs of dementia in someone with Down syndrome are easy to miss if you are only watching for memory loss. Behavioral changes — withdrawal, apathy, irritability, anxiety, loss of initiative — typically appear first, often years before the kind of forgetfulness most people associate with Alzheimer’s. New-onset seizures, changes in gait, and declines in the ability to plan and complete familiar routines are additional red flags. Because people with Down syndrome have varying baseline cognitive abilities, detecting decline requires knowing the individual’s own starting point, which is why baseline assessments beginning in the 30s are so strongly recommended.
Families should not let the statistics — a 90 percent-plus lifetime risk, amyloid plaques by age 40, a mean diagnosis age in the early 50s — lead to fatalism. Alzheimer’s is not a certainty for every person with Down syndrome, and early detection paired with proper medical evaluation can rule out treatable conditions, connect families with support, and ensure the person receives the best possible care. Start the conversation with your loved one’s doctor now, even if everything seems fine. The best time to establish a baseline is before you need one.
Frequently Asked Questions
At what age should I start watching for signs of dementia in my family member with Down syndrome?
Experts recommend beginning baseline cognitive and functional assessments in the 30s. While clinical dementia symptoms most commonly appear in the late 40s to 50s, the underlying brain changes begin much earlier. Annual or biannual assessments allow clinicians to detect subtle shifts against the person’s own documented history.
My loved one with Down syndrome has always had memory difficulties. How can I tell if it is getting worse?
This is one of the central diagnostic challenges. The key is to watch for a change from the person’s own baseline, not to compare them against general population norms. If they could previously remember their daily schedule and now cannot, or if they handled a routine independently and now need prompting, that decline is meaningful regardless of where they started. The NTG-EDSD screening tool is specifically designed to capture these informant-reported changes.
Could the behavioral changes be caused by something other than dementia?
Yes, and this must be investigated before assuming dementia. Thyroid problems, depression, chronic ear or sinus infections, vision loss, and sleep apnea are all more common in people with Down syndrome and can all cause behavioral and cognitive changes that mimic dementia. A thorough medical workup should always come first.
Does every person with Down syndrome eventually get Alzheimer’s?
No. While the lifetime risk exceeds 90 percent and nearly all individuals develop amyloid plaques and tau tangles by age 40, having brain pathology is not the same as having clinical dementia. The National Down Syndrome Society emphasizes that Alzheimer’s is not inevitable. Roughly 30 percent in their 50s and about 50 percent in their 60s develop diagnosable dementia, meaning a significant proportion do not.
How fast does dementia progress once symptoms appear in someone with Down syndrome?
Research from Washington University School of Medicine has found that Alzheimer’s disease progresses faster in people with Down syndrome compared to the general population. The timeline from early symptoms to significant functional decline is typically compressed, which makes early detection and care planning especially important.
What screening tool should be used for dementia in people with Down syndrome?
The NTG-EDSD (National Task Group – Early Detection Screen for Dementia) is the recommended screening instrument. It is completed by a caregiver or someone who knows the person well. Two or more areas of concern suggest mild cognitive impairment, while three to five or more concerns indicate progression toward dementia.
