FMRpolyG-positive inclusions in CNS and non-CNS organs of a fragile X premutation carrier with fragile X-associated tremor/ataxia syndrome

Fragile X-associated Tremor/Ataxia syndrome (FXTAS), a late-onset monogenetic neurodegenerative disorder, is caused by a CGG-repeat expansion (55-200) in the 5′ UTR of the fragile-X mental retardation 1 gene (FMR1) on the X-chromosome [1]. The prevalence of the FMR1 premutation (PM) is about 1:855 in males and 1:291 in females [2]. Approximately 45.5% of male and 16.5% of female PM carriers older than 50 years will develop signs of FXTAS [3]. In addition to the core features of tremor and gait ataxia, unexplained medical co-morbidities have been reported, including thyroid disease, cardiac arrhythmias, hypertension, migraine, impotence, and neuropathy [4]. PM carriers have increased levels of FMR1 mRNA (2 to 8 fold in leucocytes) and normal to slightly reduced FMR1 protein (FMRP) levels [5]. The current hypothesis is that FXTAS is caused by an RNA gain-of-function mechanism. Ubiquitin-positive intranuclear inclusions, are found in both brain and non-central nervous system (CNS) organs of patients with FXTAS [6,7]. So far, it is not clear whether these inclusions are protective or toxic. Recently, it has been hypothesized that repeat-associated non-AUG (RAN) translation plays a role in disease process and inclusion formation. Todd et al. [8] demonstrated that through initiation at a near-ATG codon located in the 5′UTR of the FMR1 gene a polyGlycinecontaining protein, FMRpolyG, is expressed. This protein accumulates in ubiquitin-positive inclusions in Drosophila, cell culture, mouse disease models and brain from FXTAS patients. To investigate the link between FMRpolyG