When a patient's memory symptoms start young and relatives were affected at similar ages, doctors order a familial Alzheimer's panel — a single blood or saliva test that sequences three genes, APP, PSEN1 and PSEN2 — so that the result is in hand when the memory clinic appointment happens. Running it beforehand changes what the visit is for: instead of opening a question, the clinician arrives with either a cause for the dementia or a cleared genetic explanation, and spends the hour on treatment, family planning and monitoring.
Those three genes are the only ones known to directly cause Alzheimer's disease. Nearly all Alzheimer's is not inherited this way — it reflects many genes interacting with age, lifestyle and environment, and researchers have mapped at least 80 genetic regions that nudge risk. The panel is reserved for the small group whose family pattern looks like single-gene inheritance.
Medical information disclaimer: This article is for general educational purposes only and does not provide medical advice, diagnosis, or treatment. Always consult a physician or other qualified health professional about symptoms, medications, tests, or treatment decisions.
Table of Contents
- What the panel tests, and why all three genes at once
- Who gets offered it
- How age at onset shapes the reading of a result
- The limits a clinician states out loud
- APOE is a separate test with a separate purpose
- The insurance exposure most patients are not told about
- Frequently Asked Questions
What the panel tests, and why all three genes at once
APP, PSEN1 and PSEN2 are autosomal dominant genes: a single altered copy inherited from one parent is enough to cause disease. According to the National Institute on Aging's Alzheimer's disease genetics fact sheet, these are the only three genes known to directly cause Alzheimer's, and a variant in one usually produces symptoms before age 65 — sometimes decades earlier. Clinics order the three together rather than one after another because no gene dominates enough to test first.
GeneReviews' early-onset familial Alzheimer disease table puts PSEN1 at roughly 20–70% of cases in these families, APP at about 10–15%, and PSEN2 at about 5%. Sequential testing would mean weeks of waiting between each gene, with the appointment arriving before the answer did. The commercial panel reflects that: Labcorp's hereditary Alzheimer's disease panel covers exactly APP, PSEN1 and PSEN2, and the lab will not run it unless the ordering provider attests that the patient consented to genetic testing. That attestation is not a formality — it is the point in the workflow where counseling has to have already happened.
Who gets offered it
The family history does most of the selecting. Doctors look for Alzheimer's diagnosed in a parent, sibling or grandparent at an unusually young age, across more than one generation, with ages at onset clustering rather than scattering into the eighties. Insurance policy pushes the same direction.
The Blue Cross Federal Employee Program's genetic testing policy for Alzheimer's disease covers testing a symptomatic patient who has a suggestive family history, and covers targeted testing of a person without symptoms when a first- or second-degree relative is already known to carry an APP, PSEN1 or PSEN2 variant. That sequencing matters practically. Policy expects an affected relative to be tested first where that is possible, so the family's specific variant is identified before anyone healthy is tested. A healthy person tested cold gets a far less useful answer: a negative result cannot rule out a variant the family carries if nobody has established what that variant is.
- Affected relative still living and willing — test that person first
- Known family variant on record — targeted single-site testing, cheaper and faster
- Patient symptomatic with young onset and family pattern — full three-gene panel
- No family history and no symptoms — the panel is not indicated
How age at onset shapes the reading of a result
A result is not read in isolation. The clinic compares the patient's own age at first symptoms with the onset range typical for whichever gene came back altered, because that comparison decides whether the variant explains the illness or sits beside it. GeneReviews records distinct ranges by gene. PSEN1 typically causes symptoms in the 40s or early 50s, with a range from the 30s to the early 60s.
APP onset usually falls in the 40s to 50s. PSEN2 is the widest, running from about age 40 to 75. So a PSEN1 variant in someone whose symptoms began at 44 is a clean explanation. The same variant in someone whose symptoms began at 79 raises a different question, and the clinic will keep looking for other contributors — vascular disease, medications, mood, sleep — rather than closing the workup.
The limits a clinician states out loud
A positive result does not set a date. PSEN2 shows what geneticists call reduced penetrance: some people carrying the variant are still unaffected past 80. A published PSEN2 phenotype and genotype series recorded onset spanning ages 45 to 88 in carriers. Telling a 50-year-old carrier anything precise about when symptoms will start would misrepresent what the test can do.
Variant interpretation has its own limits. Before disclosing a result, the Blue Cross FEP policy directs clinicians to check the reported variant against the Alzheimer Disease and Frontotemporal Dementia Mutation Database, because some published variants turn out to show incomplete penetrance or are not clearly pathogenic. A laboratory report naming a variant is the start of interpretation, not the end. Counseling is treated as a required step, not an option. Payer policy, citing the joint ACMG and NSGC practice guideline, expects formal genetic counseling before predictive testing in a person without symptoms — see Blue Shield of California's policy on genetic testing for Alzheimer's disease, which also still classes APOE risk testing in asymptomatic people as investigational.
APOE is a separate test with a separate purpose
Patients often conflate the familial panel with APOE testing, and the two answer different questions. APOE ε4 is a risk variant, not a cause, which is why it is not part of the three-gene panel and why payers do not cover it as a predictive test in healthy people. It does have a defined clinical role once treatment is on the table.
FDA labeling for both anti-amyloid drugs says APOE ε4 testing should be performed before starting treatment, to inform the risk of ARIA — amyloid-related imaging abnormalities, swelling or small bleeds in the brain seen on MRI. In donanemab trials, the FDA prescribing information for Kisunla reports ARIA in 55% of ε4 homozygotes, 36% of heterozygotes and 25% of noncarriers. So a patient may legitimately have both tests ordered, for unrelated reasons: the panel to find a cause, APOE to set a safety margin on a drug.
The insurance exposure most patients are not told about
The question worth raising before testing is not medical. The Genetic Information Nondiscrimination Act bars genetic discrimination by health insurers and employers — and stops there. It does not cover life insurance, disability insurance or long-term care insurance, the three products most relevant to someone considering a dementia risk test.
People consistently get this wrong, including people who believe they understand the law. In a survey of GINA knowledge, 92.6% of respondents who rated their own knowledge of the act as high answered that question incorrectly. The practical move is ordinary and easy to miss: if long-term care or disability coverage is something you want, apply for it before you test, not after. Underwriting asks what you know, and a result you already hold is a result you have to disclose.
Frequently Asked Questions
Can I order a familial Alzheimer's panel myself without a doctor?
The panel sold through Labcorp requires an ordering provider to attest that you consented to genetic testing, so it runs through a clinician rather than direct to consumer.
If my panel is negative, does that rule out inherited Alzheimer's in my family?
Not on its own. A negative result is most informative when an affected relative has already been tested and the family's specific variant is known; without that, a negative cannot exclude a variant nobody has characterized yet.
Does a positive result change which treatments I can have?
It does not restrict anti-amyloid treatment, but APOE ε4 testing is expected before starting those drugs, because carrier status changes the risk of brain swelling and bleeding on MRI.
