Neurotoxicity is a common side effect of vincristine (VCR) treatment. Severe exacerbations of neuropathy have been reported in patients with Charcot-Marie-tooth disease (CMT) 1A with duplication of the peripheral myelin protein 22 (PMP22) gene. However, whether or not VCR exacerbates neuropathies through mutations in other CMT-associated genes besides PMP22 duplication has not been well studied. The purpose of this study was to identify mutations in any CMT-associated genes in a patient with hypersensitivity to VCR. We performed clinical, electrophysiological, and genetic examinations of a 23-year-old woman, who was hypersensitive to low-dose VCR, and her healthy mother. DNA analysis was performed using our specially designed resequencing array that simultaneously screens for 28 CMT-associated genes. Electrophysiological studies revealed that the patient and her healthy mother had demyelinating polyneuropathy. Furthermore, they showed the same novel mutation in the early growth response 2 (EGR2) gene. Recognizing pre-existing asymptomatic CMT by electrophysiological studies and genetic analysis before VCR treatment allowed us to prevent severe VCR-induced neuropathy.