Diagnosing familial Alzheimer’s disease
Last Reviewed: Jul 2, 2025Diagnosing familial Alzheimer's disease (FAD) can be tricky. Because FAD is uncommon, many family doctors and some neurologists are not familiar with it.
In addition, the person experiencing symptoms may be in denial or unaware of their deficits, so it can be important for a family member to help with the diagnostic process.
Conditions with similar symptoms
Sometimes, FAD symptoms look similar to other medical issues. These include:
Depression
Other genetic early-onset diseases that cause dementia:
Frontotemporal dementia (FTD)
Lewy body dementia (LBD)
Huntington’s disease (HD)
Creutzfeldt-Jakob disease (CJD)
CADASIL
Assessments used to diagnose FAD
Doctors may use any of the following assessments in diagnosing FAD:
Medical and Family History: To look at your medical history and whether other family members have had Alzheimer's disease, what symptoms they had, and at what age they began. Three or more generations of Alzheimer’s disease can be indicative of FAD.
Physical Exam: To perform a general medical workup, such as reviewing medications, checking blood pressure, and listening to heart and lungs.
Blood Tests: To test whether memory problems stem from other health issues, like thyroid issues or vitamin deficiencies.
Neurological Exam: To test for signs of stroke or Parkinson’s by checking reflexes, coordination, eye movement, and speech.
Cognitive, Functional and Behavioral Testing: To evaluate complex memory and thought processes. The Mini-Mental State Exam (MMSE) and Montreal Cognitive Assessment (MoCA) are examples of these types of tests.
Brain Scans:
Structural brain imaging such as MRI or CT: These assess for other things that can cause neurological symptoms like hydrocephalus, strokes and tumors. They can also assess the brain shrinkage that is sometimes seen in AD.
PET Scans: FDG-PET and Amyloid PET look at how the brain uses energy and for amyloid plaques, respectively.
Lumbar Puncture: To rule out infectious or other rare causes of cognitive impairment and to evaluate levels of specific proteins (like Aβ, tau or NfL) in the cerebrospinal fluid (CSF), the fluid that surrounds the brain and spine.
Genetic Testing: To screen for mutations in APP, PSEN1, and PSEN2.
A definitive Alzheimer’s diagnosis
An Alzheimer’s diagnosis is definitive when amyloid plaques and tau tangles have been detected inside the brain. Until recently, that was only possible through an autopsy. That meant that people with Alzheimer’s disease could not be officially diagnosed until after death.
Biomarkers—short for 'biological markers'—are measurable indicators of the presence or progression of a disease. Since the brain is a well-protected organ, biomarkers provide scientists with windows into what's going on in the brain.
With new technologies to measure biomarkers, scientists can now detect amyloid plaques and tau tangles inside the living brain. This makes diagnosis and treatment possible much earlier than before.
PET scans to detect Alzheimer’s
A PET scan, or Positron Emission Tomography scan, is a type of imaging test that helps doctors see how your organs and tissues are working. In the case of neurodegenerative disease, PET scans look at markers of brain activity and amount of certain proteins in the brain.
Here are some types of PET scans used for Alzheimer’s:
FDG (Fluorodeoxyglucose) PET: Evaluates how well the brain is using sugar (glucose), which is its main source of energy. Low activity could mean Alzheimer's disease or another type of dementia. FDG PET scans are an indirect measure of the protein changes occurring in the brain.
Amyloid (PIB) PET: Detects beta-amyloid (Aβ) plaques in the brain—one of the key hallmarks of Alzheimer’s disease that tend to build up as the disease progresses.
Tau PET: Assesses the presence of tau and neurofibrillary tangles in the brain, which correlate with cognitive decline. This test is mostly used in research settings.
A PET scan can give doctors important clues about what's going on in the brain. The amount of brain activity or disease proteins (like Aβ) captured by PET can help distinguish certain types of diseases from one another and help determine disease stage.
Right now, PET scan technology is expensive and not covered by all insurances, so it is not always available.
Lumbar punctures to detect Alzheimer’s
Another way to diagnose Alzheimer’s is with cerebrospinal fluid (CSF) biomarkers. These are collected with a lumbar puncture (also known as a spinal tap). In a lumbar puncture, doctors clean and numb the person’s lower back and collect a sample of CSF, the fluid that cushions their spinal cord. Then, they’ll test the fluid, looking at one or both of the following:
Aβ: Evaluates how much Aβ, specifically Aβ1-40 and Aβ1-42, is in CSF. These specific forms of Aβ decrease over the course of the disease.
Tau: Measures the total amount of tau (total tau) and the amount of phosphorylated tau (pTau) in CSF. There are many different forms of pTau that are measured, and this list is constantly growing.
Doctors will also test the fluid for the presence of inflammation or infectious agents, which can rarely cause a progressive dementia syndrome.
Is it important to get diagnosed?
Because there’s no cure for Alzheimer’s disease, some people wonder whether it’s important to get diagnosed. Understandably, they may not want to know for sure that they or their loved one is living with a progressive neurological disease. But there are several important reasons to seek a diagnosis.
There are reversible causes of dementia that should be ruled out.
There are treatments available that can help alleviate some symptoms or even slow disease if administered early.
A diagnosis may mean access to benefits or services that would not otherwise be available.
A diagnosis could open the door to research opportunities aimed at changing the future of the disease.
It can help family members understand their own risk, and feel better informed about what future steps make sense for them.