Hereditary ataxia in four related Norwegian Buhunds

A FAM8A1 frameshift variant is associated with REM sleep behavior disorder, urinary retention, and mydriasis in Russian Blue cats

REM sleep behavior disorder (RBD) is a disease characterized by the loss of lower motor neuron inhibition responsible for skeletal muscle atonia during REM sleep. It has been reported in humans, dogs and cats, and can be idiopathic or secondary to a neurodegenerative disease. Five young adult Russian Blue cats from two related families were presented for progressively worsening RBD episodes frequently associated with urinary loss. Three of these cats also suffered urinary retention with overflow incontinence between RBD episodes. Neurological examination revealed a large bladder in three cats and a bilateral mydriasis with absent pupillary light reflexes in two cats; further examinations were unremarkable. Treatment attempts were unsatisfactory, with four cats being euthanized. Histopathology of the brain did not reveal any abnormalities. A disease-associated 23-bp deletion in exon 1 of FAM8A1 (NC_058372.1:g.11622168_11622190del), introducing a frameshift at codon 162 and a premature stop codon at codon 276 (XM_019831563.3:c.485_507del p.(Gln162Profs*115)), was identified by whole genome sequencing. The variant segregated in the affected families with a recessive mode of inheritance, showed an allele frequency of 1.5% in West-European Russian Blue cats (N = 68) and was not present in 276 cats belonging to 32 other breeds (including the closely related Nebelung breed). The variant FAM8A1 isoform is predicted to affect the assembly and activity of the endoplasmic reticulum-associated protein degradation pathway, which plays an important role in cell homeostasis. RBD and urinary retention syndrome is a hereditary encephalopathy affecting Russian Blue cats. A genetic test now allows diagnosis and prevention of this debilitating disease.

An Overview of Canine Inherited Neurological Disorders with Known Causal Variants

Hereditary neurological conditions documented in dogs encompass congenital, neonatal, and late-onset disorders, along with both progressive and non-progressive forms. In order to identify the causal variant of a disease, the main two approaches are genome-wide investigations and candidate gene investigation. Online Mendelian Inheritance in Animals currently lists 418 Mendelian disorders specific to dogs, of which 355 have their likely causal genetic variant identified. This review aims to summarize the current knowledge on the canine nervous system phenes and their genetic causal variant. It has been noted that the majority of these diseases have an autosomal recessive pattern of inheritance. Additionally, the dog breeds that are more prone to develop such diseases are the Golden Retriever, in which six inherited neurological disorders with a known causal variant have been documented, and the Belgian Shepherd, in which five such disorders have been documented. DNA tests can play a vital role in effectively managing and ultimately eradicating inherited diseases.

Phenotypic and genetic aspects of hereditary ataxia in dogs

Hereditary ataxias are a large group of neurodegenerative diseases that have cerebellar or spinocerebellar dysfunction as core feature, occurring as an isolated sign or as part of a syndrome. Based on neuropathology, this group of diseases has so far been classified into cerebellar cortical degenerations, spinocerebellar degenerations, cerebellar ataxias without substantial neurodegeneration, canine multiple system degeneration, and episodic ataxia. Several new hereditary ataxia syndromes are described, but most of these diseases have similar clinical signs and unspecific diagnostic findings, wherefore achieving a definitive diagnosis in these dogs is challenging. Eighteen new genetic variants associated with these diseases have been discovered in the last decade, allowing clinicians to reach a definitive diagnosis for most of these conditions, and allowing breeding schemes to adapt to prevent breeding of affected puppies. This review summarizes the current knowledge about hereditary ataxias in dogs, and proposes to add a "multifocal degenerations with predominant (spino)cerebellar component" category regrouping canine multiple system degeneration, new hereditary ataxia syndromes that do not fit in 1 of the previous categories, as well as specific neuroaxonal dystrophies and lysosomal storage diseases that cause major (spino)cerebellar dysfunction.

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

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.