Evaluation of the dynactin 1 gene in Leonbergers and Labrador Retrievers with laryngeal paralysis

A RAPGEF6 variant constitutes a major risk factor for laryngeal paralysis in dogs

Laryngeal paralysis (LP) is the inability to abduct the arytenoid cartilages during inspiration, resulting in a partial to complete airway obstruction and consequent respiratory distress. Different forms of LP with varying age of onset exist in dogs. Hereditary early onset forms were reported in several dog breeds. In most breeds, hereditary LP is associated with other neurologic pathologies. Using a genome-wide association study and haplotype analyses, we mapped a major genetic risk factor for an early onset LP in Miniature Bull Terriers to a ~1.3 Mb interval on chromosome 11. Whole genome sequencing of an affected Miniature Bull Terrier and comparison to 598 control genomes revealed a 36 bp insertion into exon 15 of the RAPGEF6 gene (c.1793_1794ins36). The imperfect genotype-phenotype correlation suggested a complex mode of inheritance with a major genetic risk factor involving a recessive risk allele. Homozygosity for the insertion was associated with a 10- to 17-fold increased risk for LP. The insertion allele was only found in Miniature Bull Terriers and Bull Terriers. It was absent from >1000 control dogs of other dog breeds. The insertion sequence contains a splice acceptor motif leading to aberrant splicing in transcripts originating from the mutant allele (r.1732_1780del). This leads to a frameshift and a premature stop codon, p.(Ile587ProfsTer5), removing 64% of the open reading frame. Our results suggest an important role of RAPGEF6 in laryngeal nerve function and provide new clues to its physiological significance.

Laryngeal paralysis (LP) leads to respiratory distress in affected dogs and can be fatal in severe cases. Many different forms of LP with different etiologies exist. Striking breed predispositions suggest that genetic factors contribute to some forms of LP. During the last years, dog breeders noticed an increased prevalence of an early onset LP in Miniature Bull Terriers. We mapped a major risk locus for this specific form of LP to a ~1.3 Mb interval on dog chromosome 11. Whole genome sequence analysis of an affected dog and comparison to 598 control genomes revealed a single protein-changing genetic variant in the critical interval. This variant, a 36 bp insertion into a coding exon of the RAPGEF6 gene, creates a cryptic splice site and leads to the expression of an aberrantly spliced transcript with a premature stop codon. This suggests that the insertion results in a loss-of-function allele. Dogs that are homozygous for the insertion have a 10- to 17-fold increased risk to develop LP. The genotype-phenotype association is not perfect, suggesting that other genetic and/or environmental factors also contribute to the development of LP. Our results suggest an important role of RAPGEF6 in laryngeal nerve function.