Recent studies have implicated glutamatergic targets of FMRP in hereditary cerebellar ataxias including the main cerebellar excitatory amino acid (Eaa1) transporter and a subtype of metabotropic glutamate receptor (Grm5).
Together with fragile X-associated tremor and ataxia (FXTAS) and fragile X-associated premature ovarian failure (POF)/primary ovarian insufficiency (POI), FXS depends on dysfunctional expression of the FMR1 gene on Xq27.3.
Fragile X mental retardation type 1 (FMR1) gene premutation is the first single-gene cause of primary ovarian failure (Fragile X-associated primary ovarian insufficiency [FXPOI]) and one of the most common causes of ataxia (fragile X-associated tremor/ataxia syndrome [FXTAS]), multiple additional phenotypes such as fibromyalgia, hypothyroidism, migraine headaches, sleep disturbances, sleep apnea, restless legs syndrome, central pain syndrome, neuropathy and neuropsychiatric alterations has been described.
In summary, the clinician should consider a FXTAS diagnosis and testing for the Fragile X mental retardation 1 (FMR1) gene premutation if a patient over the age of 50 (1) presents with cerebellar ataxia and/or intention tremor with mild parkinsonism, (2) has the middle cerebellar peduncle (MCP) sign, global cerebellar and cerebral atrophy, and/or subcortical white matter lesions on MRI, or (3) has a family history of fragile X related disorders, intellectual disability, autism, premature ovarian failure and has neurological signs consistent with FXTAS.
We performed quantitative gait and mobility analysis in seven FMR1 PM carriers with FXTAS and ataxia, six PM carriers without FXTAS, and 18 age-matched controls.
The frequency of FMR1 premutations was 1.9% (1/54) in our group of patients with ataxia as the primary clinical feature, and 1.2% (1/86) in the larger movement disorders group.
Following the discovery of two disorders associated with premutation alleles of the fragile X mental retardation gene (FMR1), primary ovarian insufficiency [fragile X-associated primary ovarian insufficiency (FXPOI)] and a tremor/ataxia syndrome [fragile X-associated tremor/ataxia disorder (FXTAS)], numerous studies have examined other potential co-morbid conditions, including neuropsychological deficits.
Premutation carriers of repeat expansions in the fragile X mental retardation (FMR1) gene develop kinetic tremor and ataxia or the 'fragile X associated tremor/ataxia syndrome' (FXTAS).
Fragile X-associated tremor/ataxia (FXTAS) is a late onset disorder caused by a premutation in the FMR1 gene, in which neurological symptoms are associated with white matter (wm) changes, especially within the middle cerebellar peduncles (MCP sign), seen on magnetic resonance images (MRIs).
Because of the high prevalence of FMR1 premutation in the general population, the description and characterization of the FXTAS syndrome is of great interest as it may represent one of the more common monogenic causes of ataxia, tremor, and dementia.
Expanded FMR1 alleles contribute to cases of late-onset sporadic cerebellar ataxia, suggesting that FMR1 genetic testing should be carried out in such cases.
FMR1 premutation alleles with a repeat number greater than 55 were detected in 3 probands (2.1%) from a total of 142 male subjects initially referred to our university medical center for evaluation of sporadic ataxia.
Two patients carried FMR1 premutations of 110 and 135 repeats: a man with a familial form of cerebellar ataxia and a woman diagnosed as having MSA-cerebellar type.
Screening of movement disorder patients with other clinical features of FXTAS (e.g., ataxia and parkinsonism) may be more likely to yield expanded FMR1 alleles.
We describe five female carriers of the FMR1 premutation who presented with symptoms of tremor and ataxia and who received a diagnosis of definite or probable fragile-X-associated tremor/ataxia syndrome (FXTAS).
Finally, since this syndrome may represent one of the more common single-gene causes of tremor, ataxia, and dementia among older males, FMR1 DNA testing should be considered when evaluating adult patients with tremor/ataxia.