Before genetic counseling, build a family tree covering at least three generations and record each relative's health status, symptom onset, diagnosis, and age or cause of death. Include neurologic and psychiatric symptoms—not just confirmed dementia—along with medical records and previous genetic test results when available. This clinical family tree, called a pedigree, helps a genetic counselor look for inheritance patterns and decide whether testing may be informative. It cannot prove that a family has a genetic form of dementia.
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
- Who belongs in the family tree?
- Record symptoms, not just diagnosis labels
- Which patterns are most informative?
- How can you improve the information?
- What can the pedigree tell you about testing?
Who belongs in the family tree?
Include your children, siblings, parents, and grandparents. Add other biological relatives, such as aunts, uncles, cousins, nieces, and nephews, if they had relevant symptoms or help reveal a pattern. For every relative, record: Unaffected relatives matter too.
An older relative without symptoms may influence how a possible inheritance pattern is interpreted. A relative who died young may never have reached the age when symptoms might have appeared. The ACMG/NSGC practice guideline recommends documenting both affected and unaffected relatives, including their current age or age and cause of death in a three-generation pedigree.
- Biological relationship to you
- Whether the person had relevant symptoms
- Current age, if living
- Age and cause of death, if deceased
- Dementia or neurologic diagnosis, including its subtype
Record symptoms, not just diagnosis labels
Write down the earliest neurologic or psychiatric change you can identify. This may be years earlier than the formal diagnosis.
Examples might include memory problems, personality change, language difficulty, movement symptoms, or motor-neuron disease. For each affected relative, distinguish among: This detail matters because relatives may have received broad or inconsistent labels. The NHS England National Genomics Education Programme advises including behavioral or personality change, progressive language impairment, parkinsonism, corticobasal features, and motor-neuron disease when assessing possible frontotemporal dementia in a family.
- Age at first symptoms
- Age at diagnosis
- Diagnosis or suspected dementia type
- How the diagnosis was made
- Other neurologic or psychiatric features
Which patterns are most informative?
Age at onset is one of the strongest clues. According to the University of Washington's GeneReviews overview, alzheimer disease beginning before age 50 has the highest likelihood of a genetic cause, while onset after 70 has the lowest; three or more relatives with early-onset dementia raises the probability further of a genetic explanation. Also look for a vertical pattern, meaning affected people appear in successive generations.
A characteristic autosomal-dominant Alzheimer pattern includes at least three affected people across two or more generations, with two being first-degree relatives of the third. First-degree relatives are parents, siblings, or children. Do not treat an apparently negative family history as proof that dementia is not hereditary. In GRN-related frontotemporal dementia, the family pattern may be obscured by milder symptoms, a parent's early death, or reduced penetrance—meaning a person can carry a disease-related variant without developing recognizable symptoms.
How can you improve the information?
Treat family recollections as a starting point. When possible, confirm important diagnoses through medical records, direct clinical evaluations, or copies of previous molecular genetic test results.
Useful documents may include: Focus first on relatives with the earliest onset, the clearest diagnosis, or unusual combinations of symptoms. If records are unavailable, label the information as reported or uncertain instead of presenting it as confirmed. Even partial details—such as "progressive language trouble began around age 52"—are more useful than simply writing "dementia.".
- Neurology or memory-clinic notes
- Hospital discharge summaries
- Neuropsychological assessments
- Death certificates
- Prior genetic laboratory reports
What can the pedigree tell you about testing?
A pedigree helps guide testing, but family history alone does not establish a deterministic genetic cause. The National Institute on Aging explains that routine clinical genetic testing is not generally used to diagnose or predict Alzheimer-related dementia, and APOE results alter estimated risk rather than reliably showing who will develop the disease in the future. When genetic testing is appropriate, the practical first choice is usually an affected relative.
Finding a pathogenic APP, PSEN1, or PSEN2 variant in that person can make predictive testing possible for adult relatives who have no symptoms. Testing an unaffected relative before identifying a familial variant is more likely to produce an uninformative result. If the affected relative cannot attend counseling, ask whether stored records or an existing genetic test report can be obtained. Bring the pedigree, note which details remain uncertain, and identify the affected relative most likely to be available for evaluation or testing.
