Phenotypic spectrum and incidence of TRPV4 mutations in patients with inherited axonal neuropathy

Objective: To clarify the phenotypic spectrum and incidence of TRPV4 mutations in patients with inherited axonal neuropathies. Methods: We screened for TRPV4 mutations in 169 French unrelated patients with inherited axonal peripheral neuropathy. Ninety-five patients had dominant Charcot-Marie-Tooth type 2 (CMT2) disease, and 74 patients, including 39 patients with distal hereditary motor neuropathy, 14 with congenital spinal muscular atrophy and arthrogryposis, 13 with CMT2, and 8 with scapuloperoneal spinal muscular atrophy, presented with additional vocal cord paralysis and/or skeletal dysplasia. Results: No deleterious TRPV4 mutation was identified in the 95 patients with "pure" CMT2 (0/95). In contrast, 12 of 74 patients (16%) with neuropathy and vocal cord paralysis and/or skeletal dysplasia presented pathogenic TRPV4 mutations, including 7 patients with distal hereditary motor neuropathy, 2 with scapuloperoneal spinal muscular atrophy, 2 with congenital spinal muscular atrophy and arthrogryposis, and one with CMT2. Investigation of affected relatives allowed us to study 17 patients. All patients had childhood-onset motor neuropathy and showed a variety of associated findings, including foot deformities (100% of cases), kyphoscoliosis (100%), elevated serum creatine kinase levels (100%), vocal cord paralysis (94%), scapular winging (53%), respiratory insufficiency (29%), hearing loss (24%), skeletal dysplasia (18%), and arthrogryposis (12%). Eight missense mutations were observed in these 12 families, including 2 previously unreported. Six mutations were de novo events, and 2 asymptomatic carriers were identified. Conclusion: With 16% of patients affected in our series, this study demonstrates that TRPV4 mutations are a major cause of inherited axonal neuropathy associated with a large spectrum of additional features.