Down Syndrome and Alzheimer's

Adults with Down syndrome have a very high risk of Alzheimer's, often starting in their 50s, because of an extra copy of a gene on chromosome 21; learn the early signs, how diagnosis differs, and how families can plan ahead.

Last reviewed: October 2026

Thanks to better medical care and inclusion, people with Down syndrome are living much longer than in past generations. The Alzheimer's Association notes that people with Down syndrome now live an average of about 60 years, some into their 70s. That's wonderful news—but it has revealed a serious health risk: Alzheimer's disease.

If you love or care for an adult with Down syndrome, understanding this link can help you notice changes early and plan ahead.

Why the risk is so high

Down syndrome happens when a person has an extra copy of chromosome 21. The National Institute on Aging (NIA) explains that chromosome 21 carries the gene for amyloid precursor protein (APP). An extra copy means the brain makes extra APP, which leads to a buildup of beta-amyloid plaques—a hallmark of Alzheimer's (see Amyloid and Tau Explained).

According to the NIA:

By age 40, most people with Down syndrome have amyloid plaques and tau tangles in their brains.
An estimated 50% or more of people with Down syndrome will develop dementia due to Alzheimer's as they age.
This type of Alzheimer's is not passed down from parent to child; it results from the extra chromosome itself.

The Alzheimer's Association, citing the National Down Syndrome Society, says about 30% of people with Down syndrome in their 50s and about 50% in their 60s have Alzheimer's dementia.

A major 2020 study in The Lancet of 388 adults with Down syndrome traced how Alzheimer's changes unfold. Changes in spinal-fluid amyloid appeared as early as the 20s and 30s, with memory and thinking changes typically in the 40s and 50s. The median age of diagnosis with Alzheimer's dementia was about 54. The researchers found that the risk of symptomatic Alzheimer's kept climbing with age, reaching 90–100% among people in their 60s. They called Alzheimer's and its complications the leading cause of death in adults with Down syndrome.

Not everyone with Down syndrome develops dementia, even with these brain changes. Why some people stay well longer is an active area of research.

Early signs to watch for

Memory loss may not be the first sign. The Alzheimer's Association lists early changes such as:

Less interest in socializing, talking or expressing thoughts
Less enthusiasm for usual activities
Shorter attention span
Sadness, fearfulness or anxiety
Irritability, uncooperativeness or aggression
Restlessness or sleep problems
Seizures that begin in adulthood
Changes in coordination and walking
Becoming noisier or more excitable

Families and support staff often notice changes first—like losing skills at work or a day program, needing more help with routines that were once easy, or getting lost in familiar places.

Why diagnosis is different

Standard memory tests are designed for people without intellectual disabilities, so they don't work well here. The Alzheimer's Association notes that most adults with Down syndrome won't report memory concerns themselves. Experts recommend:

Document a "baseline" by age 35. Record the person's adult abilities—daily skills, communication, work, hobbies—so later changes can be measured against their own normal. Videos and written notes are helpful.
Check regularly for changes in thinking, behavior and daily function.
Rule out other causes. Conditions common in Down syndrome can mimic dementia, including thyroid problems, depression, hearing and vision loss, chronic ear or sinus infections and sleep apnea. Many of these are treatable (see Reversible Causes of Memory Problems).
See a specialist familiar with both Down syndrome and dementia when possible.

Treatment

The Alzheimer's Association notes that the FDA has not approved any drugs specifically to treat dementia associated with Down syndrome. Doctors sometimes prescribe standard Alzheimer's medicines such as Cholinesterase Inhibitors and Memantine, but evidence in this group is limited, and experts advise caution because people with Down syndrome may process medicines differently.

Newer anti-amyloid drugs like Lecanemab (Leqembi) and Donanemab (Kisunla) were not tested in people with Down syndrome, and current use recommendations exclude them. A 2026 review explained why: people with Down syndrome tend to have more amyloid in blood vessel walls (cerebral amyloid angiopathy), which likely raises the risk of brain swelling and bleeding side effects (see ARIA: Side Effects of Anti-Amyloid Drugs). Research on safe treatment is under way.

Research and hope

Because Alzheimer's in Down syndrome follows a fairly predictable timeline, researchers see this group as especially important for prevention trials. The NIA supports:

ABC-DS (Alzheimer's Biomarker Consortium – Down Syndrome), which tracks brain changes over time
ACTC-DS and the Trial-Ready Cohort for Down Syndrome (TRC-DS), which prepare people to join future treatment trials
DS-Connect, an NIH registry where families can learn about research opportunities

See Joining a Clinical Trial.

Planning ahead

Talk early with the person, family and care team about future wishes, while the person can take part (see Legal Planning).
Plan for caregiving. Many adults with Down syndrome live with aging parents. Discuss who will provide care if a parent can no longer do so.
Adapt the home and routines for safety and simplicity (see Home Safety and Daily Care and Routines).
Find support. The National Down Syndrome Society and the Alzheimer's Association both offer resources for families.

Where to get help

Alzheimer's Association 24/7 Helpline: 800-272-3900
NIA ADEAR Center: 800-438-4380
National Down Syndrome Society: ndss.org

Sources

Not medical advice. This article is general information, not a diagnosis or treatment plan for any individual. Talk with a doctor about your situation.

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We may answer common questions in future updates (we won't share your name). We can't give personal medical advice; for urgent help call the Alzheimer's Association Helpline at 800-272-3900.

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