The neuropathy-causing GARS1∆ETAQ mutation drives pathology in subsets of motor and sensory neurons in mice

Charcot-Marie-Tooth disease type 2D (CMT2D) results from gain-of-function mutations in GARS1 , which encodes glycyl-tRNA synthetase (GlyRS), the enzyme responsible for charging transfer RNA (tRNA) with glycine. There are several CMT2D mouse models, but Gars ∆ETAQ/+ is the only one that bears a patient-sourced mutation. Created using CRISPR/Cas9 to model a 12-nucleotide de novo GARS1 deletion identified in an unusually severe CMT2D patient, Gars ∆ETAQ/+ mice have previously been shown to display several neuromuscular phenotypes: motor axon loss, denervated neuromuscular junctions (NMJs) and reduced muscle function. Here, we extend these analyses to provide a more comprehensive understanding of both motor and sensory nerve deficits across hind- and fore-limbs. At 3 months, Gars ∆ETAQ/+ mice possess sex-independent alterations in the levels of neuropathy biomarkers – including decreased NfL and increased periaxin – alongside reduced muscle endurance and strength, and impairments in the sensory modalities of mechanosensation, proprioception and nociception. Underpinning these dysfunctions, we identified site-specific defects comprising altered sensory neuron populations, muscle spindle loss, reduced motor neuron size, disrupted NMJ innervation and maturation, and reduced axonal transport of signalling endosomes in vivo . Together, these experiments show that Gars ∆ETAQ/+ mice display robust and selective peripheral nerve pathology that manifests in a general length-dependent fashion, priming this CMT2D allele for testing treatments and evaluating mechanisms underlying peripheral nerve vulnerability.