Primary ciliary dyskinesia in two English Cocker Spaniels

NME5 frameshift variant in Alaskan Malamutes with primary ciliary dyskinesia

Primary ciliary dyskinesia (PCD) is a hereditary defect of motile cilia in humans and several domestic animal species. Typical clinical findings are chronic recurrent infections of the respiratory tract and fertility problems. We analyzed an Alaskan Malamute family, in which two out of six puppies were affected by PCD. The parents were unaffected suggesting autosomal recessive inheritance. Linkage and homozygosity mapping defined critical intervals comprising ~118 Mb. Whole genome sequencing of one case and comparison to 601 control genomes identified a disease associated frameshift variant, c.43delA, in the NME5 gene encoding a sparsely characterized protein associated with ciliary function. Nme5^-/- knockout mice exhibit doming of the skull, hydrocephalus and sperm flagellar defects. The genotypes at NME5:c.43delA showed the expected co-segregation with the phenotype in the Alaskan Malamute family. An additional unrelated Alaskan Malamute with PCD and hydrocephalus that became available later in the study was also homozygous mutant at the NME5:c.43delA variant. The mutant allele was not present in more than 1000 control dogs from different breeds. Immunohistochemistry demonstrated absence of the NME5 protein from nasal epithelia of an affected dog. We therefore propose NME5:c.43delA as the most likely candidate causative variant for PCD in Alaskan Malamutes. These findings enable genetic testing to avoid the unintentional breeding of affected dogs in the future. Furthermore, the results of this study identify NME5 as a novel candidate gene for unsolved human PCD and/or hydrocephalus cases.

Motile cilia are required for clearing mucous, infectious agents and inhaled dust from the airways. Primary ciliary dyskinesia (PCD) is a hereditary defect of motile cilia. Clinical findings may include recurrent airway infections, fertility problems, and sometimes hydrocephalus. We analyzed an Alaskan Malamute family, in which two out of six puppies were affected by an autosomal recessive form of PCD. Whole genome sequencing of an affected dog identified a one base pair deletion in the NME5 gene, c.43delA, leading to an early frame-shift and premature stop codon. Later in the study, we became aware of a previously published Alaskan Malamute with PCD involving respiratory infections and hydrocephalus. We observed perfect concordance of the NME5 genotypes with the PCD phenotype in all three affected Alaskan Malamutes and more than 1000 controls. The fact that the third case, which had no documented close relationship to the initial two cases, was homozygous for the same rare mutant NME5 allele, strongly supports our hypothesis that NME5:c.43delA causes the PCD phenotype. We confirmed absence of NME5 protein expression in nasal epithelium of an affected dog. Our results enable genetic testing in dogs and identify NME5 as novel candidate gene for unsolved human PCD cases.

AKNA Frameshift Variant in Three Dogs with Recurrent Inflammatory Pulmonary Disease

We investigated three related Rough Collies with recurrent inflammatory pulmonary disease. The clinical symptoms were similar to primary ciliary dyskinesia (PCD). However, the affected dogs did not carry any known pathogenic PCD variants. Pedigree analysis suggested a recessive mode of inheritance. Combined linkage and homozygosity mapping in three cases and seven non-affected family members delineated 19 critical intervals on 10 chromosomes comprising a total of 99 Mb. The genome of one affected dog was sequenced and compared to 601 control genomes. We detected only a single private homozygous protein-changing variant in the critical intervals. The detected variant was a 4 bp deletion, c.2717_2720delACAG, in the AKNA gene encoding the AT-hook transcription factor. It causes a frame-shift introducing a premature stop codon and truncates 37% of the open reading frame, p.(Asp906Alafs*173). We genotyped 88 Rough Collies consisting of family members and unrelated individuals. All three available cases were homozygous for the mutant allele and all 85 non-affected dogs were either homozygous wildtype (n = 67) or heterozygous (n = 18). AKNA modulates inflammatory immune responses. Akna-/- knockout mice die shortly after birth due to systemic autoimmune inflammatory processes including lung inflammation that is accompanied by enhanced leukocyte infiltration and alveolar destruction. The perfect genotype-phenotype association and the comparative functional data strongly suggest that the detected AKNA:c.2717_2720delACAG variant caused the observed severe airway inflammation in the investigated dogs. Our findings enable genetic testing, which can be used to avoid the unintentional breeding of affected puppies.