Similar clinical, pathological, and genetic features in Chinese patients with autosomal recessive and dominant Charcot–Marie–Tooth disease type 2K

Mutations in the ganglioside-induced differentiation-associated protein 1 gene (GDAP1) cause rare subtypes of Charcot–Marie–Tooth disease (CMT2K and CMT4A). CMT2K is an axonal neuropathy while CMT4A is a demyelinating type. In a series of 169 Chinese CMT patients (79 CMT1, 52 CMT2 and 38 unclassified), four unrelated patients (2.37%) were identified with GDAP1 mutations, including two with autosomal recessive CMT2K (AR-CMT2K) and two dominant CMT2K (AD-CMT2K). All patients had disease onset before 5 years of age, and presented with muscle weakness, atrophy, and mild sensory disturbance in distal limbs. Motor nerve conduction velocities of the median nerve were within normal ranges, and compound muscle action potential ranged from 1.5 to 3.8 mV. Sural nerve biopsy revealed loss of large myelinated fibers with regeneration clusters and a few onion bulbs. Electron microscopy showed mitochondrial aggregation in both axons and Schwann cells, and neurofilament accumulation in giant unmyelinated fibers. The p.H256R mutation was found in all patients with GDAP1 compound heterozygous mutations, suggesting that it might be a common mutation in Chinese patients. This study observed no difference in the disease onset, phenotype severity, electrophysiological findings, or pathological changes between AR-CMT2K and AD-CMT2K patients.