A PSEN1 genetic test detects disease-causing changes in PSEN1, a gene that causes inherited early-onset Alzheimer disease. When dementia symptoms progress, it offers very high laboratory accuracy, requires counseling and family history beforehand, and guides diagnosis and family planning afterward. Doctors consider it mainly when symptoms start before age 65 and relatives had early dementia. Results matter most for the person tested and for first-degree relatives.
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
- How accurate is testing after symptoms start?
- How do you prepare for the test?
- What does a positive result mean for your family?
- What are the limits and what comes next?
How accurate is testing after symptoms start?
PSEN1 changes cause autosomal-dominant early-onset Alzheimer disease with nearly complete penetrance. The Monarch Initiative reports typical onset before age 65 in its Monarch Initiative disorder summary, accounting for 20-70% of explained familial cases. Test yield depends on family pattern.
A 2021 peer-reviewed study found APP, PSEN1 and PSEN2 sequencing explains 40-80% of autosomal-dominant families, but only about 5-13% of unselected early-onset cases. ARUP Laboratories reports analytical sensitivity and specificity at or above 99% in its ARUP Consult early-onset panel page, using massively parallel sequencing with Sanger confirmation. A negative result lowers the chance of heritable disease but does not exclude it.
How do you prepare for the test?
Preparation starts with counseling, not just a sample. The American College of Medical Genetics and National Society of Genetic Counselors joint guideline describes the standard in its ACMG and NSGC practice guideline: blood or saliva sample, detailed three-generation family history, and discussion of costs, possible outcomes, and family implications.
Guidelines urge testing an affected relative first. That approach gives the clearest result for the family.
- Give a blood or saliva/buccal sample at the clinic or lab
- Gather ages of onset, diagnoses, and causes of death for three generations
- Meet for pre-test counseling about costs, outcomes, and family effects
- Identify an affected relative to test first when possible
What does a positive result mean for your family?
A confirmed harmful PSEN1 change in a person with progressing dementia supports an early-onset Alzheimer diagnosis. University of Pennsylvania medical guidance notes each first-degree relative then faces a 50% inheritance risk.
That risk prompts referral for predictive counseling, not immediate testing of everyone. Counseling covers choice, timing, privacy, and support for at-risk relatives.
What are the limits and what comes next?
A positive result does not predict exact onset age, first symptoms, severity, or speed of decline. GeneReviews notes this limit for asymptomatic carriers even when penetrance is essentially complete.
BrightFocus Foundation outlines practical follow-up in its BrightFocus genetic testing resource, updated Jan. 2025. Bring a support person to disclosure visits and ask the neurology team about prevention trial referrals.
- Return to neurology for diagnosis, treatment planning, and support services
- Discuss family planning and communication with relatives
- Offer at-risk relative testing under a Huntington-style two-visit disclosure protocol
- Ask about prevention trials and research eligibility
