Before ordering or reviewing results from an APP/PSEN1/PSEN2 genetic panel, ask whether your family history actually fits the pattern of familial Alzheimer's, whether a genetic counselor is involved before and after the test, and what a positive, negative, or inconclusive result would actually change. Familial (early-onset) Alzheimer's means symptoms before age 65 in a family with multiple affected relatives across generations, caused by a dominant mutation that gets passed down with each child having a 50% chance of inheriting it, per an NIH/National Institute on Aging fact sheet. New memory symptoms in someone with that kind of family history raise a different set of questions than memory symptoms in someone without one. The sections below walk through what the panel covers, who it's meant for, how to read the result, and what to ask before agreeing to be tested.
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
- Which Genes Does the Panel Actually Test?
- Who Should Actually Be Offered This Panel?
- What Does a Positive or Negative Result Actually Mean?
- Should You Also Ask About APOE?
- What to Ask the Genetic Counselor Before Testing
Which Genes Does the Panel Actually Test?
The familial Alzheimer's panel looks at three genes: APP on chromosome 21, PSEN1 on chromosome 14, and PSEN2 on chromosome 1. A mutation in any one of them is inherited in an autosomal dominant pattern, which is why the NIH fact sheet puts each child of a carrier at a 50% risk of inheriting the same mutation, regardless of sex. The three genes are not equally common causes.
PSEN1 mutations account for roughly 80% of autosomal dominant Alzheimer's cases and are fully penetrant, meaning essentially everyone who carries one eventually develops the disease, according to a review hosted by the National Institutes of Health. PSEN2 mutations cause about 5% of cases, carry roughly 95% penetrance, and tend to produce a later average age of onset than PSEN1. This is a different test from the consumer APOE reports some people have already seen advertised. APP, PSEN1, and PSEN2 testing is specifically for early-onset, strongly familial disease; APOE is a separate, more common variant tied to later-onset risk and is covered in Section 4.
Who Should Actually Be Offered This Panel?
The 2011 joint guideline from the American College of Medical Genetics and Genomics and the National Society of Genetic Counselors sets the clinical bar: testing should be offered to a person with early-onset Alzheimer's symptoms who has a family history of dementia, or whose family history is unknown, and to the close relatives of someone already confirmed to carry a mutation, as described in the ACMG/NSGC joint practice guideline. In every case, the guideline calls for genetic counseling alongside the test, not just a lab order. That framing matters for new memory symptoms.
A single relative with Alzheimer's in their 80s, with no other pattern across generations, looks very different from a parent and grandparent who both developed dementia in their 50s. The panel is built for the second picture, not the first — ask directly whether your family history matches the pattern the guideline describes before pursuing it. If it doesn't match, that's worth saying out loud to whoever is evaluating the new symptoms, since it changes which questions are worth pursuing next.
What Does a Positive or Negative Result Actually Mean?
A positive result in PSEN1 is about as close to certain as genetics gets — full penetrance means essentially every carrier develops the disease. A positive PSEN2 result carries roughly 95% penetrance and often a later onset, so the practical timeline differs even though the genetic conclusion is similarly strong, per the same NIH-hosted review. A negative result is where the questions multiply.
Early-onset cases make up only about 2–10% of all Alzheimer's diagnoses, and even within that early-onset group, a mutation in APP, PSEN1, or PSEN2 turns up in only about 30–50% of cases, according to a clinical policy citing the American Clinical Laboratory Association. A negative panel does not rule out a hereditary cause — it rules out these three specific genes, and the family pattern may still reflect something else not yet identified. Ask whoever orders the test, before results come back, what a negative result will and won't settle for your family. That conversation is easier to have before the report arrives than after.
Should You Also Ask About APOE?
APOE is a different gene from APP, PSEN1, and PSEN2, and it works differently: it modifies risk for the much more common late-onset form of Alzheimer's rather than causing early-onset disease outright. The ACMG/NSGC guideline recommends against routine clinical APOE testing outside a genetic-counseling setting for exactly this reason — it changes risk estimates, it doesn't diagnose anything. The Alzheimer's Association has gone further, stating it does not recommend genetic testing for Alzheimer's disease for the general population, because no proven strategy currently exists to prevent the disease even once a risk gene is identified, per the Alzheimer's Association.
A consumer report like 23andMe's FDA-authorized Genetic Health Risk test only checks the APOE ε2/ε3/ε4 variants and does not evaluate the roughly 30 other genes known to influence late-onset risk, so it is not a substitute for clinical evaluation. There is one setting where APOE status has become directly actionable: anyone being considered for the anti-amyloid drug lecanemab (brand name Leqembi) should have APOE ε4 genotyping done first. The current FDA prescribing label requires this because ε4 homozygotes — about 15% of Alzheimer's patients — have a higher rate of serious brain-swelling or bleeding side effects (called ARIA) than heterozygotes or noncarriers, according to the FDA drug label. If lecanemab or a similar drug is on the table after new memory symptoms, ask whether APOE testing has been done for that reason specifically, separate from any familial-panel discussion.
What to Ask the Genetic Counselor Before Testing
Pretest genetic counseling should cover more than the biology of the gene itself. A medical policy on familial Alzheimer's testing outlines that counseling should address the limits of a predictive result and its possible consequences for health, life, and disability insurance, employment or educational discrimination, and family relationships, according to a medical policy document.
Those consequences apply before symptoms appear in an at-risk relative, not just after a diagnosis. Useful questions to bring to that conversation: A counselor can walk through each of these before a sample is drawn, which is the point at which the answers are most useful.
- Does my family history match the early-onset, multi-generation pattern this panel is designed to evaluate, or does it look more like typical late-onset Alzheimer's?
- If the result is negative, what does that rule out, and what does it leave open?
- Who else in my family would learn they're at risk if I test positive, and have they been part of this conversation?
- Could this result affect my eligibility for life, disability, or long-term care insurance before I apply for it?
- If I'm also being evaluated for an anti-amyloid treatment, has APOE genotyping been ordered separately, and for that specific purpose?
