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PubMed This is a summary of 15 peer-reviewed journal articles Updated
Neurology

The Road to a Diagnosis: Genetics and Imaging

At a Glance

A definite diagnosis of Fragile X-associated tremor/ataxia syndrome (FXTAS) requires both an FMR1 genetic premutation blood test and specific clinical evidence. This includes major physical symptoms like an intention tremor combined with hallmark brain MRI findings, such as the MCP sign.

Navigating the diagnosis of FXTAS often requires a combination of genetic testing, detailed brain imaging, and careful clinical observation. Because its symptoms overlap so significantly with more common conditions, many patients find themselves on a “diagnostic odyssey,” sometimes being treated for the wrong disease for years [1][2]. Understanding the specific criteria used for a “Definite” FXTAS diagnosis can help you advocate for the right tests.

The Two Pillars of Diagnosis

To be diagnosed with Definite FXTAS, a patient must meet two main requirements:

  1. Genetic Confirmation: A blood test must show an FMR1 premutation, which is defined as having between 55 and 200 CGG repeats [3][4].
  2. Clinical AND Radiological Evidence: This strict criteria requires both a major physical symptom (like intention tremor or cerebellar ataxia) AND a major finding on a brain MRI [5][6].

Auditing Your MRI Report

When you look at your radiology report, you are looking for specific “bright spots” (called T2 or FLAIR hyperintensities) in two key areas of the brain:

  • The MCP Sign: This is a bright spot in the middle cerebellar peduncles, the “bridges” that connect the cerebellum (balance center) to the rest of the brain [7][8]. This is considered a hallmark of FXTAS.
  • The Splenium Sign: This is a bright spot in the splenium of the corpus callosum, which is the back part of the structure that connects the left and right sides of the brain [9][6].

If your report mentions “white matter changes” or “atrophy” (shrinking) without mentioning these specific areas, it may be worth asking your doctor to have the scans re-reviewed by a neuroradiologist familiar with FXTAS [8][10]. It is also important to note that MRIs are primarily used to establish the diagnosis of FXTAS; doctors typically do not order regular, ongoing MRIs just to track the progression of these bright spots, as symptoms are tracked clinically.

Differentiating FXTAS from Similar Conditions

It is very common for FXTAS to be mistaken for other movement disorders. Here is how doctors tell them apart:

  • Parkinson’s Disease (PD): In PD, the tremor usually happens at rest (while the hand is still) and often improves with a medication called Levodopa [1]. In FXTAS, the tremor is typically an intention tremor (it starts when you move toward a target) and usually does not respond well to Parkinson’s medications [11].
  • Essential Tremor (ET): ET is very common and often involves a tremor when the hands are held out or moving [11]. However, ET usually does not involve the severe balance problems (ataxia) or the specific MRI bright spots seen in FXTAS [12].
  • Neuronal Intranuclear Inclusion Disease (NIID): This is a rare condition that can look almost identical to FXTAS on an MRI [13]. The main difference is the genetic cause; while FXTAS is caused by the FMR1 gene, NIID is caused by a different gene (NOTCH2NLC) [14][15]. A skin biopsy or specific genetic testing can help tell them apart if the diagnosis is unclear [14].

By understanding these differences, you can work with your medical team to ensure your diagnosis is accurate, which is essential for managing your symptoms effectively [2].

Common questions in this guide

What is required for a definite FXTAS diagnosis?
A definite diagnosis of FXTAS requires two main criteria. A patient must have an FMR1 genetic premutation confirmed by a blood test, along with both a major physical symptom like an intention tremor and specific findings on a brain MRI.
What is the MCP sign on an MRI report?
The MCP sign is a specific bright spot seen on brain MRI scans in the middle cerebellar peduncles, which connect the balance center to the brain. Finding this sign is considered a hallmark for diagnosing FXTAS.
How is an FXTAS tremor different from Parkinson's disease?
Tremors in Parkinson's disease usually occur while the hand is resting. In contrast, FXTAS typically causes an intention tremor, meaning the shaking starts and worsens as you move your hand toward a specific target.
Can FXTAS be misdiagnosed as Essential Tremor?
Yes, FXTAS is often mistaken for Essential Tremor because both conditions cause shaking when the hands are moving. However, FXTAS also involves severe balance problems and specific brain MRI changes that are not seen in Essential Tremor.
Why might I need to have my brain MRI reviewed again for FXTAS?
If your initial MRI report mentions general white matter changes without noting specific areas like the MCP or splenium, it may be helpful to get a second opinion. A neuroradiologist familiar with FXTAS can look for the highly specific signs needed for an accurate diagnosis.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Does my radiology report specifically mention 'T2/FLAIR hyperintensity' in the middle cerebellar peduncles or the splenium of the corpus callosum?
  2. 2.Is my tremor classified as an intention tremor or a resting tremor, and how does that affect my diagnosis?
  3. 3.How did you rule out other conditions like Parkinson's disease or Essential Tremor in my case?
  4. 4.Would you recommend a skin biopsy or additional genetic testing to rule out Neuronal Intranuclear Inclusion Disease (NIID)?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (15)
  1. 1

    Fragile X-Associated Tremor/Ataxia Syndrome (FXTAS): Pathophysiology and Clinical Implications.

    Cabal-Herrera AM, Tassanakijpanich N, Salcedo-Arellano MJ, Hagerman RJ

    International journal of molecular sciences 2020; (21(12)) doi:10.3390/ijms21124391.

    PMID: 32575683
  2. 2

    Prevalence of Fragile X-Associated Tremor/Ataxia Syndrome in Patients with Cerebellar Ataxia in Japan.

    Higuchi Y, Ando M, Yoshimura A, et al.

    Cerebellum (London, England) 2022; (21(5)):851-860 doi:10.1007/s12311-021-01323-x.

    PMID: 34498198
  3. 3

    Parkinsonism Versus Concomitant Parkinson's Disease in Fragile X-Associated Tremor/Ataxia Syndrome.

    Salcedo-Arellano MJ, Wolf-Ochoa MW, Hong T, et al.

    Movement disorders clinical practice 2020; (7(4)):413-418 doi:10.1002/mdc3.12942.

    PMID: 32373658
  4. 4

    Mild Neurological Signs in FMR1 Premutation Women in an Unselected Community-Based Cohort.

    Mailick MR, Hong J, Movaghar A, et al.

    Movement disorders : official journal of the Movement Disorder Society 2021; (36(10)):2378-2386 doi:10.1002/mds.28683.

    PMID: 34117786
  5. 5

    Fragile X-Associated Tremor/Ataxia Syndrome (FXTAS).

    Zafarullah M, Tassone F

    Methods in molecular biology (Clifton, N.J.) 2019; (1942()):173-189 doi:10.1007/978-1-4939-9080-1_15.

    PMID: 30900185
  6. 6

    Fragile X-associated tremor/ataxia syndrome: An under-recognised cause of tremor and ataxia.

    Kalus S, King J, Lui E, Gaillard F

    Journal of clinical neuroscience : official journal of the Neurosurgical Society of Australasia 2016; (23()):162-164 doi:10.1016/j.jocn.2015.08.010.

    PMID: 26439425
  7. 7

    Presence of Middle Cerebellar Peduncle Sign in FMR1 Premutation Carriers Without Tremor and Ataxia.

    Famula JL, McKenzie F, McLennan YA, et al.

    Frontiers in neurology 2018; (9()):695 doi:10.3389/fneur.2018.00695.

    PMID: 30186228
  8. 8

    FXTAS presenting with cervical dystonia as the initial symptom: Considering FXTAS in the clinical evaluation of cervical dystonia.

    Funasaka H, Kanazawa S, Kamada S

    eNeurologicalSci 2025; (40()):100578 doi:10.1016/j.ensci.2025.100578.

    PMID: 40756593
  9. 9

    The Corpus Callosum Splenium Sign in Fragile X-Associated Tremor Ataxia Syndrome.

    Hall DA, Hermanson M, Dunn E, et al.

    Movement disorders clinical practice 2017; (4(3)):383-388 doi:10.1002/mdc3.12449.

    PMID: 30363360
  10. 10

    Clinical Heterogeneity in a Scandinavian FMR1 Premutation Carrier Cohort and Basal Ganglia Atrophy in FXTAS.

    Berglund S, Hashim F, Laffita-Mesa J, et al.

    Cerebellum (London, England) 2026; (25(1)):19.

    PMID: 41686285
  11. 11

    Tremorography in fragile X-associated tremor/ataxia syndrome, Parkinson's disease and essential tremor.

    Robertson EE, Hall DA, Pal G, et al.

    Clinical parkinsonism & related disorders 2020; (3()):100040 doi:10.1016/j.prdoa.2020.100040.

    PMID: 34316626
  12. 12

    Digital gait markers to potentially distinguish fragile X-associated tremor/ataxia syndrome, Parkinson's disease, and essential tremor.

    Robertson-Dick EE, Timm EC, Pal G, et al.

    Frontiers in neurology 2023; (14()):1308698 doi:10.3389/fneur.2023.1308698.

    PMID: 38162443
  13. 13

    Ultra-high-field 7-Tesla magnetic resonance imaging in fragile X tremor/ataxia syndrome (FXTAS).

    Lakhani DA, Agarwal AK, Middlebrooks EH

    The neuroradiology journal 2024; 19714009241247464 doi:10.1177/19714009241247464.

    PMID: 38644331
  14. 14

    Adult-onset neuronal intranuclear inclusion disease mimicking Fragile X-associated tremor-ataxia syndrome in ethnic Chinese patients.

    Lim SY, Ishiura H, Ramli N, et al.

    Parkinsonism & related disorders 2020; (74()):25-27 doi:10.1016/j.parkreldis.2020.03.025.

    PMID: 32289521
  15. 15

    Trinucleotide CGG Repeat Diseases: An Expanding Field of Polyglycine Proteins?

    Boivin M, Charlet-Berguerand N

    Frontiers in genetics 2022; (13()):843014 doi:10.3389/fgene.2022.843014.

    PMID: 35295941

This page provides educational information about the diagnosis of FXTAS. Always consult a neurologist or genetic counselor for accurate medical evaluation and MRI interpretation.

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