Canine RNF170 Single Base Deletion in a Naturally Occurring Model for Human Neuroaxonal Dystrophy

Background Neuroaxonal dystrophy (NAD) is a group of inherited neurodegenerative disorders characterized primarily by the presence of spheroids (swollen axons) throughout the central nervous system. In humans, NAD is heterogeneous, both clinically and genetically. NAD has also been described to naturally occur in large animal models, such as dogs. A newly recognized disorder in Miniature American Shepherd dogs (MAS), consisting of a slowly progressive neurodegenerative syndrome, was diagnosed as NAD via histopathology. Objectives To describe the clinical and pathological phenotype together with the identification of the underlying genetic cause. Methods Clinical and postmortem evaluations, together with a genome‐wide association study and autozygosity mapping approach, followed by whole‐genome sequencing. Results Affected dogs were typically young adults and displayed an abnormal gait characterized by pelvic limb weakness and ataxia. The underlying genetic cause was identified as a 1‐bp (base pair) deletion in RNF170 encoding ring finger protein 170, which perfectly segregates in an autosomal recessive pattern. This deletion is predicted to create a frameshift (XM_038559916.1:c.367delG) and early truncation of the RNF170 protein (XP_038415844.1:(p.Ala123Glnfs*11)). The age of this canine RNF170 variant was estimated at ~30 years, before the reproductive isolation of the MAS breed. Conclusions RNF170 variants were previously identified in human patients with autosomal recessive spastic paraplegia‐85 (SPG85); this clinical phenotype shows similarities to the dogs described herein. We therefore propose that this novel MAS NAD could serve as an excellent large animal model for equivalent human diseases, particularly since affected dogs demonstrate a relatively long lifespan, which represents an opportunity for therapeutic trials. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society. We describe a new adult‐onset neurodegenerative disease in dogs, clinically exhibiting slowly progressive ataxia and histopathologically characterized as neuroaxonal dystrophy. Genetic analyses identified a 1‐bp (base pair) deletion in RNF170 revealing that these dogs represent a naturally occurring model for autosomal recessive spastic paraplegia 85 and autosomal dominant sensory ataxia 1.