Clinical findings and prevalence of the mutation associated with primary ciliary dyskinesia in Old English Sheepdogs

Abstract

Background: Primary ciliary dyskinesia (PCD) is generally a recessively inherited disorder characterized by dysfunction of motile cilia. A mutation in a new causative gene (CCDC39) has been identified in the Old English Sheepdog (OES).

Objectives: To describe the clinical findings and the molecular changes of affected dogs and estimate the worldwide prevalence of the mutation in a large cohort of OES.

Animals: 578 OES, including 28 affected and 550 clinically healthy dogs.

Methods: This retrospective study reviewed the data of OES diagnosed with PCD and OES tested for the mutation. Clinical data including results of physical examination and further investigations were obtained on 11/28 dogs. CCDC39 expression was assessed by qRT-PCR and Western blot analysis in affected dogs and healthy dogs. DNA was extracted on 561/578 dogs and a genetic test by Taqman technology was developed to genotype the CCDC39 mutation in these dogs.

Results: Clinical findings were recurrent nasal discharge and cough, pyrexia, leucocytosis, and bronchopneumonia. Ultrastructural defects were characterized by central microtubular abnormalities and decreased number of inner dynein arms (IDAs). Molecular analysis revealed a reduced expression of CCDC39 RNA and an absence of CCDC39 protein in affected dogs compared to healthy dogs. The mutation was more frequent in nonrandomly selected European OES population with a higher proportion of carriers (19%) compared to non-European dogs (7%).

Conclusion and clinical importance: CCDC39 mutation is dispersed in a worldwide population and is responsible for PCD in this breed. Genetic testing might enable control of this disease.

Keywords: Bronchopneumonia; CCDC39; Ciliary dysfunction; Dog; Genetic.

Figure 1

Spermatozoa from an affected dog after Diff‐quick protocol staining, showing normal morphology (A), shortened flagella (B), and narrowed midpiece (C).

Figure 2

Electron microscopy of respiratory cilia from an affected OES showing the absence of IDAs (1) in all ciliary sections, and axonemal disorganization with mislocalized peripheral doublet and displacement of the central pair (2). Magnification of the axoneme showing a normal ciliary axonema (A), isolated absence of IDAs (B), and axonemal disorganization with mislocalized peripheral doublet and displacement of the central pair (C), suggesting a loss of nexin links and radial spokes.

Figure 3

Pedigree of affected OES including 13 affected litters and 28 dogs with compatible clinical signs. The pedigree analysis was compatible with an autosomal recessive inherited pattern. All affected dogs and all their parents (obligated carriers) were at least linked once with the same common ancestor bitch (circled). Dogs 1–11 are dogs subsequently confirmed with the homozygous mutation in CCDC39.

Figure 4

qRT‐PCR showing marked reduction in CCDC39 expression within bronchial tissue from 2 affected dogs compared to 2 control dogs. Two different amplicons were used.

Figure 5

Western blot showing the presence of the CCDC39 protein in tracheal, bronchial, and testicular samples from healthy patient with the expected size of 110.4 kDa and the absence of the protein in tracheal and bronchial samples (*) from affected dog. (1) Colored Ladder, (2) Bronchi (Affected), (3) Trachea (Affected), (4) Testis (Healthy), (5) Bronchi (Healthy), and (6) Trachea (Healthy).