Fragile X-Associated Tremor/Ataxia Syndrome (FXTAS)
Consensus of the FXTAS Task Force and the Fragile X Clinical & Research Consortium
Of note, about 20% of women with the FMR1 premutation develop fragile X-associated primary ovarian insufficiency (FXPOI). Women with FXPOI do not have an increased risk of FXTAS compared with women who carry premutations and have normal ovarian function. In addition, classic FXTAS phenomenology and imaging abnormalities have been reported in FMR1 gray zone carriers (41-54 CGG repeats)10,11 and in those with a full mutation that is unmethylated or mosaic with a premutation12-14. However, FXTAS cases with repeat sizes outside of the premutation range are rare.
Table 1 outlines the clinical diagnostic criteria on which FXTAS is based. Three levels are used to indicate the confidence of a diagnosis given symptom manifestations at the time of evaluation.
Table 1. FXTAS Diagnostic Criteria in Carriers of a FMR1 Premutation
|Level of confidence|
|Definite||Presence of 1 major radiological sign plus 1 major clinical symptom|
|Probable||Presence of either 1 major radiological sign plus 1 minor clinical symptom or has the 2 major clinical symptoms.|
|Possible||Presence of 1 minor radiological sign plus 1 major clinical symptom|
|Major||MRI white matter lesions in MCPs or CCS and/or brain stem|
|Minor||MRI white matter lesions in cerebral white matter|
|Minor||Moderate to severe generalized atrophy|
|Minor||MRI white matter lesions in the splenium of the corpus callosum|
|Minor||Moderate to severe short-term memory deficiency|
|Minor||Executive function deficit|
|Minor||Neuropathy in lower extremities|
|Major||FXTAS intranuclear eosinophilic inclusions that are ubiquitin positive|
Adapted from Berry-Kravis et al, 200715
Testing for FXTAS
A diagnosis of FXTAS is confirmed by testing for a premutation-sized CGG repeat expansion in FMR1 DNA in patients with a suggestive constellation of symptoms. Findings from a brain imaging study (primarily magnetic resonance imaging (MRI)) can aid in the diagnosis. Table 2 outlines who should be tested for an FMR1 premutation given their presentation of neurological symptoms.
Table 2. Guidelines for Whom to Test for FXTAS
|Cerebellar ataxia||If is 50 years or older and the cause is unknown|
|Action tremor||If is 50 years or older and the cause is unknown; AND if also has cerebellar ataxia, parkinsonism, or dementia|
|Dementia||If is 50 years or older and the cause is unknown; AND if also has cerebellar ataxia, parkinsonism, or action tremor|
|Multiple system atrophy cerebellar subtype||Especially if a prolonged course|
|Some FXTAS signs + family history of fragile X-associated disorders or related symptoms||Patient who has symptoms of FXTAS (e.g., action tremor, cerebellar ataxia) AND has a family history of ovarian insufficiency (including infertility) OR congenital intellectual disability or Autism Spectrum Disorder; family history of individuals diagnosed with fragile X syndrome, FXPOI, or FXTAS; family members who have been diagnosed with an FMR1 mutation.|
Adapted from Berry-Kravis et al, 200715
Current Treatment Guidelines
The goal of therapy for FXTAS is to reduce symptoms and eventually to slow the progression of disease. Management of FXTAS is complex and involves appropriate follow-up by an adult neurologist. It is also important to evaluate other potential causes of dementia such as vitamin B12 deficiency, folate deficiency, and depression. Treatable causes of cerebellar ataxia should be considered in cases with significant gait symptoms. This typically includes testing liver and renal function, vitamin E, copper, thyroid function, autoimmune (SSA/SSB, ANA, Gad-65, Celiac), and paraneoplastic disorders16. Reversible causes of neuropathy should also be considered, including diabetes, monoclonal proteins, and vitamin B12 deficiency. Additionally, individualized care regarding possible adverse events from medications is essential. Referral to physical therapy and/or rehabilitative medicine, urology, genetic counseling, and social work should be considered.
Currently, intervention is limited to symptomatic therapy as there have been no effective medications based on controlled clinical trials. Treatment recommendations are based on anecdotal reports and knowledge of other disorders that are similar to FXTAS4,9. For example, action tremor and parkinsonism in FXTAS may respond to medications used for essential tremor and Parkinson disease, respectively. Action tremor may respond to B-blockers, primidone, and topiramate. Deep brain stimulator surgery can be considered for tremor. Unilateral surgery with non-traditional targets may be less likely to worsen ataxia or cognition after surgery. Medications for cerebellar dysfunction can be considered, such as amantadine, buspirone, varenicline, riluzole, or ampyra, although none have proven efficacy in FXTAS or other inherited ataxias. Treatment of psychiatric symptoms with selective serotonin inhibitors may be effective, although patients need to be monitored for worsening of balance.
It is important to note that treatments for FXTAS should be individualized as symptoms vary in every individual. Treatments should also be approached globally utilizing medications, psychological counseling, rehabilitative interventions such as speech, occupational and physical therapy, and gait training. Consideration should also be given to supportive services and counseling for the family. Specialty fields helpful in the care of individuals with FXTAS include neurology, psychiatry, psychology, rehabilitation, urology, cardiology, and movement disorders neurology.
Genetic counseling for individuals with FXTAS and their family members is recommended, due to the inheritance of the X-linked FMR1 expansion mutation. All daughters of men diagnosed with FXTAS (i.e., confirmed to have a premutation sized CGG repeat) are obligate FMR1 premutation carriers. For women with FXTAS (again, with confirmed premutation sized CGG repeat expansions), each child will have a 50% chance of receiving the FMR1 mutation, with the potential of their premutation expanding to a full mutation (<200 repeats). The full mutation leads to Fragile X syndrome, the most common inherited form of intellectual and developmental disabilities and the most common known single-gene cause of autism spectrum disorder (ASD). The expansion to the full mutation depends on the size and number of AGG interruptions in the premutation allele carried by the mother17.
How can I find a physician who is knowledgeable about FXTAS?
Fragile X Clinical and Research Consortium clinics can provide information or referral to a neurologist or other physician with experience in caring for patients with FXTAS. The National Fragile X Foundation can also provide information at 800-688-8765 or firstname.lastname@example.org.
Author note: This guideline document was written and reviewed by members of the Fragile X Clinical & Research Consortium (FXCRC) and by members of the International FXTAS consortium. It has been approved by and represents the current consensus of this group of clinical and research experts.
The Fragile X Clinical & Research Consortium was founded in 2006 and exists to improve the delivery of clinical services to families impacted by fragile X syndrome and to develop a research infrastructure for advancing the development and implementation of new and improved treatments. Members of the International FXTAS consortium (IFA) also contributed to this report. Please contact the National Fragile X Foundation for more information. (800-688-8765 or fragilex.org)
- Hagerman, R. J. et al. Intention tremor, parkinsonism, and generalized brain atrophy in male carriers of fragile X. Neurology 57, 127-130 (2001).
- Hunter, J. et al. Epidemiology of fragile X syndrome: a systematic review and meta-analysis. American journal of medical genetics. Part A 164A, 1648-1658, doi:10.1002/ajmg.a.36511 (2014).
- Tassone, F. et al. FMR1 CGG allele size and prevalence ascertained through newborn screening in the United States. Genome medicine 4, 100, doi:10.1186/gm401 (2012).
- Hagerman, R. J. & Hagerman, P. Fragile X-associated tremor/ataxia syndrome – features, mechanisms and management. Nature reviews. Neurology 12, 403-412, doi:10.1038/nrneurol.2016.82 (2016).
- Jacquemont, S. et al. Penetrance of the fragile X-associated tremor/ataxia syndrome in a premutation carrier population. Jama 291, 460-469, doi:10.1001/jama.291.4.460 (2004).
- Jacquemont, S., Leehey, M. A., Hagerman, R. J., Beckett, L. A. & Hagerman, P. J. Size bias of fragile X premutation alleles in late-onset movement disorders. Journal of medical genetics 43, 804-809, doi:10.1136/jmg.2006.042374 (2006).
- Plenge, R. M., Stevenson, R. A., Lubs, H. A., Schwartz, C. E. & Willard, H. F. Skewed X-chromosome inactivation is a common feature of X-linked mental retardation disorders. American journal of human genetics 71, 168-173, doi:10.1086/341123 (2002).
- Hall, D. A. et al. Update on the Clinical, Radiographic, and Neurobehavioral Manifestations in FXTAS and FMR1 Premutation Carriers. Cerebellum 15, 578-586, doi:10.1007/s12311-016-0799-4 (2016).
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- Liu, Y., Winarni, T. I., Zhang, L., Tassone, F. & Hagerman, R. J. Fragile X-associated tremor/ataxia syndrome (FXTAS) in grey zone carriers. Clinical genetics 84, 74-77, doi:10.1111/cge.12026 (2013).
- Pretto, D. I. et al. Intranuclear inclusions in a fragile X mosaic male. Translational neurodegeneration 2, 10, doi:10.1186/2047-9158-2-10 (2013).
- Loesch, D. Z. et al. Fragile X-associated tremor/ataxia phenotype in a male carrier of unmethylated full mutation in the FMR1 gene. Clinical genetics 82, 88-92, doi:10.1111/j.1399-0004.2011.01675.x (2012).
- Santa Maria, L. et al. FXTAS in an unmethylated mosaic male with fragile X syndrome from Chile. Clinical genetics 86, 378-382, doi:10.1111/cge.12278 (2014).
- Berry-Kravis, E. et al. Fragile X-associated tremor/ataxia syndrome: clinical features, genetics, and testing guidelines. Movement disorders : official journal of the Movement Disorder Society 22, 2018-2030, quiz 2140, doi:10.1002/mds.21493 (2007).
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- Nolin, S. L. et al. Fragile X full mutation expansions are inhibited by one or more AGG interruptions in premutation carriers. Genetics in medicine : official journal of the American College of Medical Genetics 17, 358-364, doi:10.1038/gim.2014.106 (2015).
Tremor: A quivering or shaking movement that happens when you are not trying to do it (involuntary). Action tremor occurs when you’re actively trying to do something. Rest tremor occurs when the muscles are at rest, and you are not trying to move.
Ataxia: Loss of control or incoordination of body movements
- Cerebellar ataxia: A loss of body control caused by differences in the cerebellum, the part of the brain that coordinates movement. The first signs that someone has cerebellar ataxia might be bad balance and walking, and uncoordinated eye movements. It can cause poor articulation when speaking or slurred speech, which is called dysarthria.
Appendicular ataxia: A form of cerebellar ataxia that lowers coordination mostly in the arms, hands, legs, and feet
Parkinsonism: A combination of symptoms including tremor, slow movements, rigidity or muscles being tensed, and unsteadiness
Autonomic dysfunction : Changes to the autonomic nervous system. The autonomic nervous system controls things like heart rate, body temperature, breathing rate, and sensation or feeling. Dysfunction or changes in the autonomic nervous system can lead to very high or low heart rates, sweating too much or too little, weakness, and other symptoms.
Peripheral neuropathy: Caused by damage to the peripheral nerves, which are the nerves that send information from you brain and spinal cord to the rest of your body. This often feels like stabbing, burning, or tingling, especially in the hands and feet.
- Sensory neuropathy: Caused by damage to the sensory nerves (these are the nerves that sense pain or temperature). It may feel similar to peripheral neuropathy, and people may also have reduced ability to sense pain or very hot or cold temperatures.
Tandem gait: Often done as part of a neurologic examination, or during an exam with a Neurologist. Walking so that with each step, the toes of the back foot touch the heels of the front foot.
Cerebellar dysarthric “scanning” speech: Words are broken into separate syllables, often with a pause between the syllables, and with each syllable spoken at different volumes.
Oculomotor: Having to do with eye movement.
Executive functioning: Executive functioning is an umbrella term for the skills requiring mental control and self-regulation. Executive functioning skills include inhibition (the ability to stop your behavior at the appropriate time), the ability to shift easily from one situation to another, the ability to regulate your emotional responses, and others. Impairment in executive function occurs when a person has difficulties with one or more of the executive function skills.
Temporal sequencing : A sequence of events happening in a period of time. Remembering the order of events is important to our everyday lives.