Prevalence and characterisation of FMR1 gene's premutation carriers amongst older males presenting with tremor/ataxia

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The study concerns a novel form of progressive neurological disorder associated with tremor and body imbalance occurring in older males and caused by a small expansion of the trinucleotide (CGG) repeat in a fragile X (FMR1) gene. This expansion is termed 'premutation', in contrast with the full mutation, where a large expansion of the CGG repeat in this gene causes Fragile X Syndrome, a common form of intellectual disability. While brain anomaly in the full mutation is caused by a deficit of the FMR1 specific protein product (FMRP), the pathways from premutation to a neurological disorder are unknown. In this disorder, neurological dysfunction is associated with brain atrophy visible in magnetic resonance (MRI) images. Molecular studies showed increased levels of 'messenger' RNA (mRNA), which indicates overexpression of FMR1 gene . Our own study showed significantly increased (41.7%) prevalence of neurological involvement in male premutation carriers aged >50, compared with age-matched norms. Moreover, a screening of patients with two neurological disorders associated with tremor showed a significant increase of premutation carriers (5%- 22%). The aim of this study is to test hypotheses about the association of late-onset neurological disorders of unknown cause presenting tremor and imbalance, with a fragile X premutation in males, by screening for the presence of this premutation; and then conducting a full assessment of the identified premutation carriers, including detailed neurological, neuropsychological and MRI tests, to establish the spectrum of neurological involvement. This involvement will be correlated with the molecular (DNA, mRNA, FMRP) findings. The results will contribute to understanding the mechanisms of neurological involvement caused by this premutation. Moreover, estimation of the prevalence of this premutation in relevant neurological disorders will impact on standard diagnostic, and possibly future treatment approaches in neurology clinics.