Discuss a familial Alzheimer's genetic panel the way the result actually arrives: as one piece of an existing diagnosis, interpreted with a genetic counselor, with the care partner in the room. That means asking three questions in order — what exactly did the lab classify, what does that change about the diagnosis and treatment, and who else in the family is affected by the answer.
A familial Alzheimer's panel tests the three genes that cause autosomal dominant Alzheimer's disease: *APP*, *PSEN1* and *PSEN2*. Autosomal dominant means a single copy of the variant is enough to cause disease, and each child of a carrier has a 50% chance of inheriting it. These panels are ordered during a workup for someone who already has symptoms, which shapes every conversation that follows.
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
- Why the result lands inside a diagnosis, not on its own
- What the lab report actually says
- The "how long do I have" question after a positive result
- If the panel included APOE, it may change treatment
- Settle the insurance and relative-notification questions before anyone else is tested
- Frequently Asked Questions
Why the result lands inside a diagnosis, not on its own
The Alzheimer's Association's DETeCD-ADRD specialty-care guideline tells dementia specialists to consider genetic testing only when a patient already has an established cognitive-behavioral syndrome plus a family history suggesting autosomal dominant inheritance, and to involve a genetic counselor throughout — the 2025 guideline in *Alzheimer's & Dementia* frames the panel as a confirmatory step, not a screening test. That framing is worth stating out loud at the appointment.
The question on the table is not "does this person have dementia" — the workup has already answered that — but "do we now know the cause." The guideline also says a deterministic mutation, though uncommon, raises diagnostic confidence enough to move a patient from a "suspected" to a "definite" category for Alzheimer's disease or frontotemporal lobar degeneration, and directs clinicians to include the care partner in diagnosis and disclosure in most situations. Ask whether the care partner will be present before the result is released, rather than after.
What the lab report actually says
Read the classification line, not the gene name. A systematic re-evaluation of previously reported *APP*, *PSEN1* and *PSEN2* variants under ACMG-AMP criteria, published in 2021, classified most as pathogenic or likely pathogenic but left roughly 5% as variants of uncertain significance, with *PSEN1* holding the largest number of pathogenic variants. A variant of uncertain significance neither confirms nor excludes familial Alzheimer's disease.
It is not a weak positive. Questions worth asking: A negative panel deserves the same care. *PSEN1* accounts for 30%–70% of early-onset familial Alzheimer's, *APP* for no more than 10%–15%, and *PSEN2* for under 5%; laboratories put overall detection in convincingly autosomal dominant families at only 60%–80%, per the GeneReviews chapter on early-onset familial Alzheimer disease. In a family with three affected generations, a negative result is common and does not overturn the family history.
- Which gene, and what is the exact variant notation?
- Is it classified pathogenic, likely pathogenic, uncertain, likely benign, or benign?
- If uncertain, will the lab recontact us when the classification changes?
- Was the panel sequencing only, or did it also test for deletions and duplications?
The "how long do I have" question after a positive result
Families ask for a number, and there is a defensible way to answer. In the Dominantly Inherited Alzheimer Network, reported by Bateman and colleagues in the *New England Journal of Medicine*, parental age at symptom onset averaged 45.7 years with a standard deviation of 6.8 years, and each carrier's expected onset was estimated from the mean onset age for that specific mutation, falling back on the affected parent's own onset age. Two things follow.
The estimate is mutation-specific, so ask the counselor what is known about onset for your variant rather than for familial Alzheimer's in general. And the spread matters as much as the mean — a 6.8-year standard deviation is a window, not a date. A later DIAN analysis in *Neurology* in 2024 found that life-experience factors, including higher conscientiousness, predicted delayed onset in dominantly inherited Alzheimer's disease. The mutation and family background set the window; they do not fix the day.
If the panel included APOE, it may change treatment
When anti-amyloid treatment is on the table, the calculation changes. In the CLARITY AD trial, symptomatic ARIA-E — amyloid-related imaging abnormalities with brain swelling — occurred in 9% of *ApoE* ε4 homozygotes, compared with 2% of heterozygotes and 1% of noncarriers, and the Alzheimer's Association's lecanemab clinician toolkit recommends *APOE* genotyping for all consenting patients considered for lecanemab before starting it.
Outside the United States the same genotype can decide eligibility outright. The UK summary of product characteristics indicates lecanemab for *APOE4* heterozygous carriers and non-carriers and advises against its use in homozygotes. If a relative is weighing treatment in another country, the *APOE* result is not merely a monitoring variable.
- APOE* is a susceptibility gene, not a causative one — an ε4 copy raises risk without determining outcome. The joint ACMG/NSGC practice guideline recommends *APP*/*PSEN1*/*PSEN2* testing for a symptomatic person with early-onset Alzheimer's and a family history of dementia, but states that susceptibility testing such as *APOE* is not clinically recommended where autosomal dominant Alzheimer's is unlikely, because of poor predictive value, and advises against direct-to-consumer *APOE* testing.
Settle the insurance and relative-notification questions before anyone else is tested
GINA, the Genetic Information Nondiscrimination Act, is narrower than most families assume. According to the National Human Genome Research Institute, its protections do not extend to long-term care, life, or disability insurance, where insurers may use genetic and family-history information in coverage and premium decisions, and its employment provisions apply only to employers with 15 or more employees. The practical consequence is a sequencing problem.
An at-risk relative who wants long-term care or disability coverage generally has a stronger position applying before predictive testing than after, so raise the gap before a relative tests, not once a result is in hand. Then decide, with the counselor, who in the family will be told and by whom. A positive result in the person being worked up is predictive information about their siblings and children, none of whom consented to learn it. Testing an unaffected relative is predictive testing, a separate process with its own counseling, and it is their decision to decline.
Frequently Asked Questions
Does a negative familial panel mean the dementia in our family is not inherited?
No. Detection rates in convincingly autosomal dominant families run only 60%–80%, so a negative panel leaves the family history standing and does not rule out an undiscovered cause.
Should healthy adult children get tested when a parent's panel comes back positive?
That is predictive testing, a separate decision with its own counseling. Insurance timing, the absence of GINA protection for long-term care and life coverage, and whether the person wants to know all belong in that conversation first.
Can a variant of uncertain significance be reclassified later?
Yes. Classifications change as evidence accumulates, which is why it is worth asking the laboratory whether it will recontact the ordering clinician if your variant is reclassified.
