RESUMEN
The biallelic pathogenic repeat (AAGGG)400-2000 intronic expansion in the RFC1 gene has been recently described as the cause of cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS) and as a major cause of late-onset ataxia. Since then, many heterozygous carriers have been identified, with an estimated allele frequency of 0.7% to 4% in the healthy population. Here, we describe in two affected CANVAS sisters the presence of the nonsense c.724C > T p.(Arg242*) variant in compound heterozygosity with the pathogenic repeat expansion in the RFC1 gene. Further RNA analysis demonstrated a reduced expression of the p.Arg242* allele in patients confirming an efficient nonsense-mediated mRNA decay. We also highlight the importance of considering the sequencing of the RFC1 gene for the diagnosis, especially in patients with CANVAS diagnosis carriers of the AAGGG repeat expansion.
Asunto(s)
Vestibulopatía Bilateral , Ataxia Cerebelosa , Enfermedades del Sistema Nervioso Periférico , Proteína de Replicación C , Neuronitis Vestibular , Humanos , Ataxia/genética , Vestibulopatía Bilateral/genética , Ataxia Cerebelosa/genética , Ataxia Cerebelosa/diagnóstico , Enfermedades del Sistema Nervioso Periférico/diagnóstico , Enfermedades del Sistema Nervioso Periférico/genética , Síndrome , Enfermedades Vestibulares/genética , Neuronitis Vestibular/genética , Proteína de Replicación C/genéticaRESUMEN
A method to precisely calibrate the oscillation amplitude in dynamic scanning force microscopy is described. It is shown that the typical electronics used to process the dynamic motion of the cantilever can be adjusted to transfer the thermal noise of the cantilever motion from its resonance frequency to a much lower frequency within the typical bandwidth of the corresponding data acquisition electronics of a scanning force microscopy system. Based on this concept, two procedures for the calibration of the oscillation amplitude are proposed. One is based on a simple calculation of the root mean square deviation measured at the outputs of the electronics used to process the dynamic motion of the cantilever, and the second one is based on analysis of the corresponding spectrum and the calculation of the quality factor, the resonance frequency and the signal strength.We show that the proposed scheme for amplitude calibration using thermal noise is experimentally and theoretically robust, with soft as well as with hard cantilevers. Moreover, it is directly related to well-defined quantities such as the force constant and thermal energy, in contrast to the calibration using amplitude versus distance curves, which requires non-trivial a priori assumptions regarding the amplitude versus distance relation.