Expanding the phenotype of SLC12A6-associated sensorimotor neuropathy.

Hereditary motor and sensory neuropathy with agenesis of the corpus callosum (HMSN/ACC) is a rare autosomal recessive condition characterised by early-onset severe progressive neuropathy, variable degrees of ACC and cognitive impairment. Mutations in SLC12A6 (solute carrier family 12, member 6) encoding the K+-Cl- transporter KCC3 have been identified as the genetic cause of HMSN/ACC. We describe fraternal twins with compound heterozygous mutations in SLC12A6 and much milder phenotype than usually described. Neither of our patients requires assistance to walk. The female twin is still running and has a normal intellect. Charcot-Marie-Tooth Examination Score 2 was 8/28 in the brother and 5/28 in the sister. Neurophysiology demonstrated a length-dependent sensorimotor neuropathy. MRI brain showed normal corpus callosum. Genetic analysis revealed compound heterozygous mutations in SLC12A6, including a whole gene deletion. These cases expand the clinical and genetic phenotype of this rare condition and highlight the importance of careful clinical phenotyping.

Genotype/phenotype correlations in AARS-related neuropathy in a cohort of patients from the United Kingdom and Ireland.

Charcot-Marie-Tooth disease (CMT) is the most common inherited neuropathy with heterogeneous clinical presentation and genetic background. The axonal form (CMT2) is characterised by decreased action potentials indicating primary axonal damage. The underlying pathology involves axonal degeneration which is supposed to be related to axonal protein dysfunction caused by various gene mutations. The overlapping clinical manifestation of CMT2 with distal hereditary motor neuropathy (dHMN) and intermediate CMT causes further diagnostic difficulties. Aminoacyl-tRNA synthetases have been implicated in the pathomechanism of CMT2. They have an essential role in protein translation by attaching amino acids to their cognate tRNAs. To date six families have been reported worldwide with dominant missense alanyl-tRNA synthetase (AARS) mutations leading to clinically heterogeneous axonal neuropathies. The pathomechanism of some variants could be explained by impaired amino acylation activity while other variants implicating an editing defect need to be further investigated. Here, we report a cohort of six additional families originating from the United Kingdom and Ireland with dominant AARS-related neuropathies. The phenotypic manifestation was distal lower limb predominant sensorimotor neuropathy but upper limb impairment with split hand deformity occasionally associated. Nerve conduction studies revealed significant demyelination accompanying the axonal lesion in motor and sensory nerves. Five families have the c.986G>A, p.(Arg329His) variant, further supporting that this is a recurrent loss of function variant. The sixth family, of Irish origin, had a novel missense variant, c.2063A>G, p.(Glu688Gly). We discuss our findings and the associated phenotypic heterogeneity in these families, which expands the clinical spectrum of AARS-related neuropathies.