Diagnosing familial Alzheimer’s disease
Last Reviewed: Feb 22, 2026Familial Alzheimer's disease (FAD) is considered a rare disease due to its low frequency in the general population, which means that many family physicians and some neurologists are not familiar with it. For this reason, reaching a diagnosis of FAD can be complicated.
In addition, the person experiencing symptoms may be in denial or unaware of their deficits, so it can be important for a close friend or relative to help with the diagnostic process.
Conditions with similar symptoms
Sometimes, FAD symptoms look similar to other medical issues. These include:
Depression
Frontotemporal dementia (FTD)
Lewy body dementia (LBD)
Huntington's disease (HD)
Creutzfeldt-Jakob disease (CJD)
Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL)
Assessments used to diagnose FAD
Accessing an FAD diagnosis involves the collaborative work of different specialists (e.g., in genetics, neurology, neuropsychology). Healthcare professionals may use the following techniques and evaluations to diagnose 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. Newer blood tests, approved by the FDA in 2025, can also detect Alzheimer's biomarkers like amyloid and tau — offering a less invasive alternative to PET scans and lumbar punctures.
Neurological Exam: Performed by examining reflexes, coordination, eye movements, and speech. Used to detect and rule out signs that may indicate another neurological condition, such as stroke or Parkinson's disease.
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 Alzheimer's disease..
PET Scans: Amyloid PET evaluates the abnormal accumulation of amyloid-beta protein (Aβ) in the brain, and FDG-PET measures how the brain uses glucose.
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 CSF is a fluid that circulates through the brain and spinal cord.
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. The brain is an organ well protected by the skull and it is difficult to access for studies using direct samples. Until several years ago, diagnosis was only possible through an autopsy—meaning 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 absence of the disease, as well as the stage of the disease the person is in.
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. Biomarkers in CSF, PET, MRI, and blood are used for the diagnosis of Alzheimer's. In May 2025, blood tests for diagnosing Alzheimer's disease were approved by the FDA.
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 study provides clues for the medical interpretation of what is occurring in the brain. PET detects the amount of brain activity or Alzheimer's-related proteins (such as Aβ), which helps differentiate certain types of diseases from one another and determine the stage of the disease.
Currently, PET technology is expensive, is not covered by all insurance plans, and not all cities have facilities with this service, 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.
It can help with understanding the cognitive and behavioral changes the person experiences over time.