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Peripheral myelin protein 22 (PMP22) related neuropathies account for over 50% of inherited peripheral neuropathies. A gene copy variation results in CMT1A (duplication) and hereditary neuropathy with liability to pressure palsies (HNPP; single deletion). Point mutations comprise both phenotypes. The underlying pathological mechanisms are incompletely understood and biallelic mutations of PMP22 are very rare. We describe a 9‐year‐old girl who presented before the age of 1 year with severe locomotor delay. She now requires support for standing and walking in view of her severe sensory ataxia. Strikingly, her muscle power and bulk are close to normal in all segments. Nerve conduction studies showed sensory‐motor velocities below 5 m/s. Genetic analysis revealed a homozygous sequence change in the PMP22 gene causing the loss of termination codon (c.483A > G; p.[*161Trpext*10]), extending the protein by 9 amino acids. Both heterozygous parents have neurophysiological abnormalities consistent with HNPP, consistent with this being a loss‐of‐function mutation. PMP22‐deficient human models are rare but important to decipher the physiological function of the PMP22 protein in vivo. The predominance of large fiber sensory involvement in this and other rare similar cases suggests a pivotal role played by PMP22 in the embryogenesis of dorsal root ganglia in humans. [ABSTRACT FROM AUTHOR]

Introduction: Charcot-Marie-Tooth (CMT) disease type 1A is the most common form of CMT. The main clinical features are distal weakness, sensory loss, and skeletal deformities. Although pain is a frequent complaint, small fiber involvement in CMT1A has not been studied extensively. Methods: We assessed pain and small fiber involvement in 49 CMT1A patients using a variety of pain scales, pain questionnaires, and thermal thresholds. Results: Forty-three of 49 patients (88%) complained of pain. The pain was localized to the feet in 61% of patients. Only 18% of patients had neuropathic pain. Cold and warm detection thresholds were elevated in 53% and 12% of patients, respectively. Conclusions: Our findings confirm that CMT1A patients have significant pain, which is more likely to be multifactorial in origin and suggests that a proportion of patients have small fiber dysfunction affecting mainly thinly myelinated Aδ fibers. [ABSTRACT FROM AUTHOR]