Background
Distal hereditary motor neuropathy (dHMN) is a heterogeneous group of diseases characterized by exclusive degeneration of peripheral motor nerves, while only 20.0-47.8% of dHMN patients are genetically identified. Recently, GGC expansion in the 5'UTR of NOTCH2NLC has been associated with dHMN. Accordingly, short tandem repeat (STR) should be further explored in genetically unsolved patients with dHMN.
Methods
A total of 128 patients from 90 unrelated families were clinically diagnosed as dHMN, and underwent a comprehensively genetic screening. Skin biopsies were conducted with routine protocols.
Results
Most patients showed chronic distal weakness of lower limbs (121/128), while 20 patients initially had asymmetrical involvements, 14 had subclinical sensory abnormalities, 11 had pyramidal impairments, five had cerebellar disturbance, and four had hyperCKmia. The rate of genetic detection was achieved in 36.7% (33/90), and the rate increased to 46.7% (42/90) if patients with variants uncertain significance were included. The most common causative genes included chaperone-related genes (8/33, 24.2%), tRNA synthetase genes (4/33, 12.1%), and cytoskeleton-related genes (4/33, 12.1%). Additionally, two dominant inherited families were attributed to abnormal expansion of GGC repeats in the 5'UTR of NOTCH2NLC; and a patient with dHMN and cerebellar symptoms had CAG repeat expansion in the ATXN2 gene. Skin biopsy from patients with GGC expansion in NOTCH2NLC revealed typical intranuclear inclusions on histological and ultrastructural examinations. Interpretations: This study further extends the genetic heterogeneity of dHMN. Given some dHMN patients may be associated with nucleotides repeat expansion, STR screening is necessary to perform in genetically unsolved patients.