Introduction

Sensory neuronopathy or ganglionopathy is a type of peripheral neuropathy characterised by primary and selective destruction of the dorsal root ganglia leading to degeneration of both central and peripheral neurites of sensory neurons.1

There is a narrow differential diagnosis for a sensory ganglionopathy which includes paraneoplastic (anti-Hu antibodies), autoimmune (Sjogren syndrome,), toxic (cisplatin, pyridoxine) and genetic (Friedreich’s ataxia and mitochondrial disease due to POLG1 mutations) causes.2 More recently biallelic AAGGG expansion in replication factor complex subunit 1 have been identified as a major cause of sensory ataxia neuropathy, often with cerebellar and vestibular involvement (CANVAS).3 4 However, a significant fraction of patients with a sensory ganglionopathy remain genetically undiagnosed.

In 2004 Valdamanis et al identified a heterozygous p.Arg199Cys mutation in ring finger protein 170 (RNF170) responsible for a rare form of sensory ataxia in two families from eastern Canada sharing a founder haplotype.5–7 Affected cases showed progressive sensory loss and ataxia due to degeneration of the posterior columns, but normal sensory nerve conduction.

By exome-sequencing we have identified the same p.Arg199Cys RNF170 mutation in an Ecuadorian family affected by an autosomal dominant late-onset progressive sensory ganglionopathy. Unlike the previously reported cases from Eastern Canada, affected members showed evidence of ganglionic/postganglionic involvement of the sensory peripheral nerves. Also, bilateral vestibular areflexia was identified in the index case, mimicking CANVAS.