The neurofilament light chain (NF-L) is a major constituent of intermediate filaments and plays a pivotal function in the assembly and maintenance of axonal cytoskeleton. Mutations in the NF-L gene (NEFL) cause autosomal dominant neuropathies that are classified either as axonal Charcot-Marie-Tooth (CMT) type 2E (CMT2E) or demyelinating CMT type 1F (CMT1F). The pathophysiological bases of the disorder(s) are elusive. We performed a mutational analysis of NEFL in a series of 177 index cases with CMT and without mutations in the genes for peripheral myelin protein zero (MPZ), peripheral myelin protein 22 (PMP22) and connexin 32 (GJB1); the motor nerve conduction velocity (MNCV) at the median nerve was below 38 m/s in 76 cases and above 38 m/s in 101. We identified five new pedigrees with four mutations in the head and rod domains of NF-L, including a novel Leu268Pro substitution and a novel del322Cys_326Asn deletion. Several examined affected members exhibited marked variability in the severity of disease and age at onset. Nerve conduction alterations were consistent with an axonal neuropathy often associated with demyelinating features, such as prolonged distal latencies (DL). Pathological examination of sural nerve biopsies in the probands detected in four cases a chronic axonal neuropathy dominated by focal accumulations of NF with axonal swellings (giant axons) and significant secondary demyelination; in the fifth case no NFs accumulations were evident but many myelinated fibres consisted exclusively of microtubules with few or absent NF. The pathological phenotype correlated with the pattern of nerve conduction alterations and indicated that NEFL mutations cause a profound alteration of the cytoskeleton possibly related to defective targeting of NF.

The axonal type 2 Charcot-Marie-Tooth disease (CMT2) is phenotypically poorly characterized. Here the authors report a family with a Pro22Ser mutation in the neurofilament-light gene (NF-L; CMT2E) manifesting electrophysiologically as the demyelinating type 1 CMT (CMT1) and pathologically as an axonopathy with giant axons and accumulation of disorganized NF. NF-L should be investigated in CMT2 as well as in CMT1 not associated with the usual genes PMP22, Cx32, and P0.

BackgroundEvaluation of cystic fibrosis transmembrane conductance regulator (CFTR) functional activity to assess new therapies and define diagnosis of cystic fibrosis (CF) is cumbersome. It is known that leukocytes express detectable levels of CFTR but the molecule has not been characterized in these cells. In this study we aim at setting up and validating a blood test to evaluate CFTR expression and function in leukocytes.DescriptionWestern blot, PCR, immunofluorescence and cell membrane depolarization analysis by single-cell fluorescence imaging, using the potential-sensitive DiSBAC2(3) probe were utilized. Expression of PKA phosphorylated, cell membrane-localized CFTR was detected in non-CF monocytes, being undetectable or present in truncated form in monocytes derived from CF patients presenting with nonsense mutations. CFTR agonist administration induced membrane depolarization in monocytes isolated from non-CF donors (31 subjects) and, to a lesser extent, obligate CFTR heterozygous carriers (HTZ: 15 subjects), but it failed in monocytes from CF patients (44 subjects). We propose an index, which values in CF patients are significantly (p<0.001) lower than in the other two groups. Nasal Potential Difference, measured in selected subjects had concordant results with monocytes assay (Kappa statistic 0.93, 95%CI: 0.80–1.00).Results and SignificanceCFTR is detectable and is functional in human monocytes. We also showed that CFTR-associated activity can be evaluated in 5 ml of peripheral blood and devise an index potentially applicable for diagnostic purposes and both basic and translational research: from drug development to evaluation of functional outcomes in clinical trials.