ObjectiveDevelopment of biomarkers for Charcot‐Marie‐Tooth (CMT) disease is critical for implementing effective clinical trials. The most common form of CMT, type 1A, is caused by a genomic duplication surrounding the PMP22 gene. A recent report (Neurology 2018;90:e518–3524) showed elevation of neurofilament light (NfL) in plasma of CMT1A disease patients, which correlated with disease severity. However, no plasma/serum biomarker has been identified that is specific to Schwann cells, the most directly affected cells in CMT1A.MethodsWe used the Olink immuno PCR platform to profile CMT1A patient (n = 47, 2 cohorts) and normal control plasma (n = 41, two cohorts) on five different Olink panels to screen 398 unique proteins.ResultsThe TMPRSS5 protein (Transmembrane protease serine 5) was elevated 2.07‐fold (P = <0.0001) in two independent cohorts of CMT1A samples relative to controls. TMPRSS5 is most highly expressed in Schwann cells of peripheral nerve. Consistent with early myelination deficits in CMT1A, TMPRSS5 was not significantly correlated with disease score (CMTES‐R, CMTNS‐R), nerve conduction velocities (Ulnar CMAP, Ulnar MNCV), or with age. TMPRSS5 was not significantly elevated in smaller sample sets from patients with CMT2A, CMT2E, CMT1B, or CMT1X. The Olink immuno PCR assays confirmed elevated levels of NfL (average 1.58‐fold, P < 0.0001), which correlated with CMT1A patient disease score.InterpretationThese data identify the first Schwann cell‐specific protein that is elevated in plasma of CMT1A patients, and may provide a disease marker and a potentially treatment‐responsive biomarker with good disease specificity for clinical trials.

Objective:To determine if microRNA’s (miR) are elevated in the plasma of individuals affected by the inherited peripheral neuropathy Charcot-Marie-Tooth Disease, type 1A (CMT1A), miR profiling was employed to compare control and CMT1A plasma.Methods:We performed a screen of CMT1A and control plasma samples to identify miRs that are elevated in CMT1A using next generation sequencing, followed by validation of selected miRs by quantitative PCR, and correlation with protein biomarkers and clinical data: Rash-modified CMT Examination and Neuropathy Scores (CMTES-R and CMTNS-R), ulnar compound muscle action potentials (CMAP), and motor nerve conduction velocities (MNCV).Results:After an initial pilot screen, a broader screen confirmed elevated levels of several muscle-associated miRNAs (miR1, -133a, -133b, and -206, known as myomiRs) along with a set of miRs that are highly expressed in Schwann cells of peripheral nerve. Comparison to other candidate biomarkers for CMT1A (e.g. Neurofilament L, NfL) measured on the same sample set shows a comparable elevation of several miRs (e.g. miR133a, -206, -223) and ability to discriminate cases from controls. NfL levels were most highly correlated with miR133a. In addition, the putative Schwann cell miRs (e.g. miR223, -199a, -328, -409, and -431) correlate with the recently described TMPRSS5 protein biomarker that is most highly expressed in Schwann cells and also elevated in CMT1A plasma.Conclusions:These studies identify a set of miRs that are candidate biomarkers for clinical trials in CMT1A. Some of the miRs may reflect Schwann cell processes that underlie the pathogenesis of the disease.Classification of Evidence:This study provides Class III evidence that a set of plasma miRs are elevated in patients with CMT1A.