Currently only 25-30% of patients with axonal forms of Charcot-Marie-Tooth disease (CMT) receive a genetic diagnosis.
A team of clinicians aimed to identify the causative gene of CMT type 2 in 8 non-related French families with a distinct clinical phenotype. They collected clinical, electrophysiological, and laboratory findings and performed genetic analyses in four different French laboratories. Seventy-two patients with autosomal dominant inheritance were identified. The disease usually started in the fourth decade and the clinical picture was dominated by sensory ataxia (80%), neuropathic pain (38%), and length-dependent sensory loss to all modalities. Electrophysiological studies showed a primarily axonal neuropathy, with possible isolated sensory involvement in milder phenotypes. Disease severity varied greatly but the clinical course was generally mild. Clinicians identified 2 novel variants in LRSAM1 gene: a deletion of 4 amino acids, p.(Gln698_Gln701del), was found in 7 families and a duplication of a neighboring region of 10 amino acids, p.(Pro702_Gln711dup), in the remaining family. A common haplotype of ~450 kb suggesting a founder effect was noted around LRSAM1 in 4 families carrying the first variant. LRSAM1 gene encodes for an E3 ubiquitin ligase important for neural functioning.
These results confirm the localization of variants in its catalytic C-terminal RING domain and broaden the phenotypic spectrum of LRSAM1-related neuropathies, including painful and predominantly sensory ataxic forms.
LRSAM1 variants and founder effect in French families with ataxic form of Charcot-Marie-Tooth type 2. Peretti A, Perie M, Vincent D, Bouhour F, Dieterich K, Mallaret M, Duval F, Goizet C, Juntas-Morales R, Magy L, Solé G, Nollet S, Not A, Léonard-Louis S, Francou B, Leguern E, Lia AS, Magdelaine C, Latour P, Stojkovic T. Eur J Hum Genet. 2019 Apr 17. doi: 10.1038/s41431-019-0403-8. [Epub ahead of print]