Doctors use the PSEN1 genetic test in a dementia second opinion to check whether a patient's early-onset symptoms, or family history of early-onset Alzheimer's, trace back to a mutation in the PSEN1 gene. PSEN1 (presenilin 1) is a gene that, when it carries a disease-causing variant, is the single most common known genetic cause of early-onset familial Alzheimer's disease. A second-opinion review matters because the standard clinical criteria used at a first memory-clinic visit miss most of the people who actually carry a pathogenic variant. A specialist reviewing the case may order or reinterpret PSEN1 sequencing specifically because the original workup never looked for it, or classified an ambiguous result too quickly.
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 PSEN1 Test Is Actually Checking For
- Why a Second Opinion Catches What the First Review Missed
- When a PSEN1 Result Is Unclear, Not Just Positive or Negative
- Why Doctors Often Test an Affected Relative First
- Genetic Counseling as Part of the Second Opinion
- Frequently Asked Questions
What the PSEN1 Test Is Actually Checking For
PSEN1 sequencing looks for inherited changes in the gene that produces presenilin 1, a protein involved in processing amyloid precursor protein in the brain. It is appropriate for symptomatic or asymptomatic adults who have a strong family history of early-onset Alzheimer's spanning multiple generations, according to Labtestsonline.org.uk, an NHS-affiliated resource. It is not recommended as a general-population screen or as a way to evaluate typical late-onset Alzheimer's.
On its own, a PSEN1 variant accounts for roughly 20% to 70% of familial early-onset Alzheimer's cases, depending on the population studied. When a lab also sequences the related genes APP and PSEN2 as part of a panel, that combined test identifies a causative variant in about 60% to 80% of familial early-onset cases overall, according to ARUP Consult. That gap between PSEN1 alone and the three-gene panel is one reason a second-opinion specialist may order broader testing than a first clinic did.
Why a Second Opinion Catches What the First Review Missed
Second-opinion memory clinics tend to find genetic causes of dementia more often than the referring clinics did, largely because they test more broadly rather than restricting testing to patients who already fit narrow eligibility rules. At the Alzheimer Center Amsterdam, a tertiary referral clinic that accepts second-opinion cases from other memory clinics, expanded genetic testing identified 34 pathogenic-variant carriers, or 3.3% of the cohort, with 24 of them symptomatic. Standard clinical eligibility criteria alone would have flagged only 15 of those carriers, or 44% of the total, according to a report published on PMC/NCBI. A separate retrospective review of 998 dementia patients at a Dutch memory clinic found causal pathogenic variants, including PSEN1, in 3.4% of patients overall.
Identifying those variants would have changed the clinical diagnosis in more than half of the carriers, according to a study in Alzheimer's Research & Therapy. That is the practical reason a second opinion exists in this context: a diagnosis built without genetic testing can be wrong in a way that only a gene result corrects. A specialist reviewing a prior diagnosis typically starts by asking three things: was PSEN1 (and the related genes) tested at all, was any variant found properly classified, and does the family history actually meet the threshold where testing adds value. Each of those questions can change the diagnosis on its own.
When a PSEN1 Result Is Unclear, Not Just Positive or Negative
A second-opinion review often focuses less on whether a variant was found and more on whether it was classified correctly. More than half of all reported PSEN1 variants are genetically "private," meaning each one has been seen in only a single patient or family. That makes it difficult for a lab to classify a given variant as disease-causing versus a variant of uncertain significance, and re-checking that classification is one of the specific things a second-opinion review should do, according to the same PMC/NCBI memory-clinic report. This distinction matters for how a patient is counseled.
A variant labeled "uncertain" should not be treated as a diagnosis, and a specialist may request updated classification data, additional relatives' results, or a repeat review before changing a patient's clinical picture based on a single lab report. Testing in someone who has only vague or equivocal symptoms, without a variant already confirmed in an affected relative, produces a predictive result rather than a diagnostic one. GeneReviews states that predictive testing of an asymptomatic at-risk adult for PSEN1-related early-onset familial Alzheimer disease is only interpretable once the specific pathogenic variant has already been identified in an affected relative, according to GeneReviews on NCBI Bookshelf. A second-opinion clinic will often draw this distinction explicitly when the first clinic did not.
Why Doctors Often Test an Affected Relative First
Each child of a parent who carries a PSEN1 pathogenic variant has a 50% chance of inheriting it. Clinical policy guidance recommends testing an affected family member first whenever possible, because the odds of finding a causative mutation fall as fewer relatives in the family are affected or as the age of onset rises, according to Blue Shield of California's medical policy on genetic testing for Alzheimer disease. In practice, this means a specialist handling a second opinion for an asymptomatic person will often ask whether a symptomatic relative has been tested yet, rather than proceeding directly with testing the person in front of them.
If no affected relative is available or willing to test, the result in an asymptomatic person carries more uncertainty, since there is no confirmed family variant to compare it against. A positive PSEN1 result does not reliably predict the age when symptoms will start, how severe they will be, which symptoms will appear, or how fast the disease will progress for that specific person, even though onset age often runs similar to affected relatives. Carriers have presented with rapidly progressing Alzheimer's, frontotemporal-dementia-like symptoms, spasticity, or seizures, according to a Blue Cross Blue Shield of Michigan policy notification issued in December 2024. A second-opinion doctor will typically walk through this range of possible outcomes rather than giving a single predicted course.
Genetic Counseling as Part of the Second Opinion
Professional genetic counseling is recommended before PSEN1 testing, particularly predictive testing in asymptomatic relatives, to address the psychological impact of a result and the risk of passing a pathogenic variant on to children, according to Topdoctors UK's medical dictionary entry on PSEN1. A second opinion that includes genetic counseling, rather than a lab report handed over without context, is one of the clearest differences between a thorough review and a rushed one. For a patient or family member weighing whether to seek this kind of second opinion, a few practical checks apply:.
- Confirm whether PSEN1 was tested alone or as part of a broader panel with APP and PSEN2.
- Ask whether any variant found was classified as pathogenic or as uncertain significance, and when that classification was last reviewed.
- Find out whether an affected relative was tested before an asymptomatic person was.
- Request genetic counseling before agreeing to predictive testing, not after a result arrives.
Frequently Asked Questions
Can a doctor diagnose Alzheimer's from a PSEN1 test alone?
No. A positive result supports a diagnosis in someone with symptoms, but testing an asymptomatic person without a confirmed family variant produces a predictive result, not a diagnostic one, per GeneReviews.
Does a negative PSEN1 result rule out familial Alzheimer's?
Not fully. Since PSEN1 explains only 20% to 70% of familial early-onset cases on its own, a negative result still leaves APP, PSEN2, or an unidentified cause on the table, per ARUP Consult.
Why would a second-opinion clinic retest someone who already had genetic testing?
Because broader testing at referral clinics has found far more carriers than standard eligibility criteria alone would flag, as seen in the Amsterdam cohort reported on PMC/NCBI.
