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We aimed to investigate the relationship between neurological compromise, respiratory parameters in wakefulness and in sleep, physiology, and morphology of phrenic nerves in patients with Charcot-Marie-Tooth disease type 1A (CMT1A). Sixteen patients with CMT1A were evaluated by spirometry, maximal expiratory and maximal inspiratory pressures (MEP, MIP), polysomnography, phrenic nerve compound muscle action potential (CMAP), and ultrasonography (roots C3,C4,C5 and phrenic nerves). Clinical disability was measured with Charcot-Marie-Tooth neuropathy score (CMT-NS; range 0-36). Two control groups, comprising 30 individuals matched for age, sex, and body mass index, were used for comparison. Ten patients were female (62%), mean age was 37.88 years (range 24-76); and CMT-NS range was 7-34. MIP was reduced in five (31%) and MEP in 12 patients (75%), although only one had restrictive respiratory dysfunction in spirometry. Apnoea-hypopnea index (AHI) was significantly higher in patients (12.01 ± 11.57/h × 5.89 ± 8.36/h; p value = 0.05) and increased in REM sleep compared with NREM (9.94 ± 10.96/h × 19.13 ± 19.93/h; p value = 0.01). There were significant correlations between CMT-NS and AHI (Pearson = 0.69; p value = 0.03); CMT-NS and MIP (Pearson = -0.691, p value = 0.003); and CMT-NS and MEP (Pearson = -0.603, p value = 0.013). Also, AHI showed negative correlation with MIP (Pearson = -0.52, p value = 0.036) and MEP (Pearson = -0.55, p value = 0.026). Phrenic nerves were enlarged in ultrasonography in all patients and presented significant correlations with CMAPs (right: Pearson = -0.554, p value = 0.026; left: Pearson = -0.558, p value = 0.025). We suggest that axonal degeneration of nerves directed to muscles of respiration might explain the high prevalence of respiratory weakness in patients with CMT1A. Clinical manifestations are frequent during sleep, where the diaphragm alone can only partially surpass the overload in breathing apparatus.