Characterisation of canine KCNIP4: A novel gene for cerebellar ataxia identified by whole-genome sequencing two affected Norwegian Buhund dogs.

Christopher A Jenkins,Lajos Kalmar,Sally L Ricketts,Hannes Lohi,Cathryn S Mellersh,Lorenzo Mari,Kaspar Matiasek,Kaisa Kyöstilä,Luisa De Risio,Ellen C Schofield

doi:10.1371/journal.pgen.1008527

Abstract

A form of hereditary cerebellar ataxia has recently been described in the Norwegian Buhund dog breed. This study aimed to identify the genetic cause of the disease. Whole-genome sequencing of two Norwegian Buhund siblings diagnosed with progressive cerebellar ataxia was carried out, and sequences compared with 405 whole genome sequences of dogs of other breeds to filter benign common variants. Nine variants predicted to be deleterious segregated among the genomes in concordance with an autosomal recessive mode of inheritance, only one of which segregated within the breed when genotyped in additional Norwegian Buhunds. In total this variant was assessed in 802 whole genome sequences, and genotyped in an additional 505 unaffected dogs (including 146 Buhunds), and only four affected Norwegian Buhunds were homozygous for the variant. The variant identified, a T to C single nucleotide polymorphism (SNP) (NC_006585.3:g.88890674T>C), is predicted to cause a tryptophan to arginine substitution in a highly conserved region of the potassium voltage-gated channel interacting protein KCNIP4. This gene has not been implicated previously in hereditary ataxia in any species. Evaluation of KCNIP4 protein expression through western blot and immunohistochemical analysis using cerebellum tissue of affected and control dogs demonstrated that the mutation causes a dramatic reduction of KCNIP4 protein expression. The expression of alternative KCNIP4 transcripts within the canine cerebellum, and regional differences in KCNIP4 protein expression, were characterised through RT-PCR and immunohistochemistry respectively. The voltage-gated potassium channel protein KCND3 has previously been implicated in spinocerebellar ataxia, and our findings suggest that the Kv4 channel complex KCNIP accessory subunits also have an essential role in voltage-gated potassium channel function in the cerebellum and should be investigated as potential candidate genes for cerebellar ataxia in future studies in other species.

Highlights

Hereditary ataxias are a group of movement disorders, typified by incoordination of gait, limbs, or eyes, primarily caused by inherited dysfunction of the cerebellum and/or its afferent or efferent pathways [1]
Hereditary ataxias, which are a group of disorders characterised by incoordination of movement, are typically incurable and there are often no disease-modifying treatments available
Canine hereditary ataxias are a notable group of movement disorders in dogs, and represent well characterised naturally occurring disease models of ataxia that can help improve our understanding of the underlying biology of the disorder in both dogs and humans

Summary

Introduction

Hereditary ataxias are a group of movement disorders, typified by incoordination of gait, limbs, or eyes, primarily caused by inherited dysfunction of the cerebellum and/or its afferent or efferent pathways [1]. In humans autosomal recessive and dominant forms of hereditary ataxia have been reported, in addition to mitochondrial, and, in the case of fragile X tremorataxia, X-linked forms. The specific diseases are often rare, and the genetic mutations can be breed-specific, hereditary ataxia is a key cause of movement disorders in dogs. Canine hereditary ataxia is typically inherited in an autosomal recessive manner, and disease-causing variants have been identified for some breeds [3,4,5,6,7,8,9,10,11,12]. Canine hereditary ataxia is a naturally occurring disease model and research into the genetics of ataxia in purebred dogs can help improve the understanding of the underlying molecular mechanisms of human disease

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