How CADASIL is usually diagnosed
Diagnosing CADASIL usually involves three parts:
- Recognizing the pattern — noticing a mix of symptoms and family history that raises the question of CADASIL in the first place.
- A brain MRI — an imaging scan of the brain that can support the picture and also help investigate other possible explanations for the symptoms.
- A conversation about genetic testing — deciding, with a clinician (and where possible a genetic counsellor), whether and how to test for a change in the NOTCH3 gene.
Occasionally, a small skin sample is examined as well when genetic results are unclear.
The most important moment is the first one
One of the most important diagnostic steps is simply thinking of CADASIL in the first place. Once it is on a clinician's list of possibilities, the rest of the evaluation follows.
Step 1 · Recognizing the pattern
Before CADASIL is a genetic test result, it's a pattern of symptoms and family history that adds up. Suspicion tends to grow when several of these appear together:
- Stroke or TIA (mini-stroke) in a younger adult — particularly without the usual risk factors (high blood pressure, smoking, diabetes)
- Migraine with aura starting in the 20s or 30s, especially if the aura is long, unusual, or affects one side of the body
- Mood changes, apathy (a loss of drive or motivation), or difficulty with focus and organization earlier than expected
- A family history of stroke, "early dementia," or unexplained neurological illness across multiple generations
- White-matter changes noticed on a brain MRI done for any reason
A number of other conditions can look similar at this stage — some genetic, some not. Sorting through them is what the rest of the pathway is for. See the list of conditions CADASIL can look like →
Step 2 · Brain MRI
A brain MRI is an important part of the evaluation. Certain patterns of change in the brain's white matter — the tissue deep inside the brain — can raise suspicion for CADASIL. But those findings can vary considerably from person to person, and the MRI on its own is not enough to confirm the diagnosis. It also helps clinicians rule out other possible explanations for the same symptoms.
In practical terms: your clinician will look for particular kinds of change in specific parts of the brain, and will note any small strokes or tiny bleeds that have already happened. What they see can help them decide whether CADASIL is a likely explanation and whether genetic testing is worth discussing.
Sometimes mistaken for MS
White-matter changes in a younger adult are often first attributed to multiple sclerosis. The MRI patterns actually differ in ways a specialist can recognise — and the two conditions are diagnosed differently. If MS has been suggested but the picture doesn't quite fit, it's worth asking whether CADASIL has been considered.
The scientific details (for clinicians and researchers)
Sequences that matter
- FLAIR — best for white-matter hyperintensities
- T2 — confirms lesion characteristics
- T1 — identifies lacunar infarcts
- SWI / GRE — detects cerebral microbleeds
- DWI — identifies acute or subacute ischemic lesions
Findings that point to CADASIL
| MRI finding | Why it matters |
|---|---|
| Confluent T2/FLAIR hyperintensities in the deep and periventricular white matter | The earliest and most consistent imaging finding; typically present by the 30s. |
| Anterior temporal pole involvement (FLAIR hyperintensity) | Highly suggestive of CADASIL — sensitivity moderate, specificity high. |
| External capsule involvement | Classic location; helps distinguish from MS and sporadic small-vessel disease. |
| Lacunar infarcts in basal ganglia, thalamus, brainstem, and centrum semiovale | Reflect the small-vessel arteriopathy. |
| Cerebral microbleeds on SWI/GRE | Increase with disease severity; have implications for antithrombotic decisions. |
| Brain atrophy | Develops over time; correlates with cognitive impairment. |
Distinguishing from MS: CADASIL spares the corpus callosum and U-fibers, classically involves the anterior temporal poles and external capsules, and is genetically defined. CSF studies are typically negative for oligoclonal bands.
Step 3 · Talking about genetic testing
Finding a disease-causing change in the NOTCH3 gene is what confirms CADASIL. The test itself is straightforward — a single blood draw is enough. Testing is often done as part of a wider gene panel these days, which lets the laboratory check for a handful of related conditions at the same time.
Genetic testing is a decision, not a screening test
A genetic test result can affect a person and their family in ways that go beyond medicine — including how someone thinks about family planning, insurance, and telling relatives. For that reason, predictive or diagnostic testing is best paired with an informed conversation about what the result may and may not mean. A genetic counsellor can help people think it through before testing. And it's worth remembering that a positive test confirms the diagnosis — it does not predict the individual's future.
What the three main results mean
- A disease-causing change was found — in the right clinical context, this confirms CADASIL.
- A change of uncertain meaning was found ("variant of uncertain significance") — sometimes further testing (like a skin biopsy) can help, and the result may be re-evaluated as more is learned over time.
- No disease-causing change was found — the diagnosis may be something else, or the change may be in a part of the gene that wasn't sequenced. A broader panel is sometimes worth considering.
The scientific details (for clinicians and researchers)
Sequencing the protein-coding regions of NOTCH3 — particularly the EGFr-encoding exons (exons 2–24, with the most action in exons 2–6) — identifies the cysteine-altering variants that cause classical CADASIL. In practice, panels covering the differential (HTRA1, COL4A1/A2, GLA, and others) are increasingly used up front.
Reporting terminology follows ACMG classification: pathogenic / likely pathogenic / variant of uncertain significance (VUS) / likely benign / benign. In the CADASIL context, a pathogenic or likely pathogenic cysteine-altering variant in NOTCH3 is diagnostic in the right clinical setting; a VUS in a domain of uncertain functional significance may warrant skin biopsy or family-based reclassification over time.
Skin biopsy (when it is used)
Before genetic testing was widely available, a small skin sample was the main way to diagnose CADASIL. It's still useful now, but only in specific situations — usually when a gene test is inconclusive. A tiny piece of skin is examined under a very high-power microscope to look for a particular kind of deposit around the small blood vessels; that deposit, when present, is very specific to CADASIL.
The scientific details (for clinicians and researchers)
- Granular osmiophilic material (GOM) on electron microscopy in the basement membrane around small dermal arteries — pathognomonic for CADASIL.
- NOTCH3 immunohistochemistry — abnormal NOTCH3 ectodomain accumulation in vessel walls.
Genetic counselling
Genetic testing for CADASIL should always be paired with genetic counselling. A counselling visit before testing helps people:
- Understand what the test can and cannot tell them
- Think through implications for siblings, parents, and children
- Anticipate the emotional impact of a positive — or negative — result
- Plan downstream care: monitoring, vascular risk management, family planning
- Discuss issues like insurance, disclosure, and workplace accommodations
Predictive testing in unaffected relatives
When a pathogenic NOTCH3 variant is identified in one family member, asymptomatic relatives may consider predictive testing. This is a deeply personal decision. Most international guidelines recommend:
- Pre-test and post-test genetic counselling
- Predictive testing only in adults (≥18 years), unless there is a clear medical indication
- Sufficient time for reflection between counselling and testing
- A care plan in place — regardless of result
Why test if there is no cure?
A diagnosis changes everything that can be optimised — blood pressure, smoking, lipid management, migraine strategy, mental health support, and trial enrolment. Many patients also describe relief at finally having a name for what they have lived with — and a plan for the years ahead.
After diagnosis: what comes next
A CADASIL diagnosis is the start of structured care, not the end of a question. Immediate priorities typically include:
- Comprehensive vascular risk assessment (BP, lipids, glucose, lifestyle)
- Migraine management plan
- Mood, sleep, and cognitive screening — with referrals as needed
- Family history mapping and counselling for relatives
- Connection to peer community and the CADASIL Global Foundation
- Discussion of registry enrolment and research participation
Our treatment & management page walks through this in detail.