Exclusion of CXCR4 as the cause of trapped neutrophil syndrome in Border Collies using five microsatellites on canine chromosome 19

Multiorgan neutrophilic inflammation in a Border Collie with "trapped" neutrophil syndrome

Trapped neutrophil syndrome is a rare congenital disease recognized in Border Collies and is characterized by persistent neutropenia with myeloid hyperplasia. The mechanism of neutropenia has not been described. We document the case of a young Border Collie diagnosed with trapped neutrophil syndrome based on clinical features, blood and bone marrow evaluation, and presence of the associated homozygous mutation. Results from flow cytometric and storage studies suggested lower neutrophil survival time. The dog had substantial neutrophilic inflammation in multiple organs, indicating that neutrophils could leave the marrow and enter tissues, making the term "trapped" neutrophil syndrome a misnomer.

A canine model of Cohen syndrome: Trapped Neutrophil Syndrome

BACKGROUND

Trapped Neutrophil Syndrome (TNS) is a common autosomal recessive neutropenia in Border collie dogs.

RESULTS

We used a candidate gene approach and linkage analysis to show that the causative gene for TNS is VPS13B. We chose VPS13B as a candidate because of similarities in clinical signs between TNS and Cohen syndrome, in human, such as neutropenia and a typical facial dysmorphism. Linkage analysis using microsatellites close to VPS13B showed positive linkage of the region to TNS. We sequenced each of the 63 exons of VPS13B in affected and control dogs and found that the causative mutation in Border collies is a 4 bp deletion in exon 19 of the largest transcript that results in premature truncation of the protein. Cohen syndrome patients present with mental retardation in 99% of cases, but learning disabilities featured in less than half of TNS affected dogs. It has been implied that loss of the alternate transcript of VPS13B in the human brain utilising an alternate exon, 28, may cause mental retardation. Mice cannot be used to test this hypothesis as they do not express the alternate exon. We show that dogs do express alternate transcripts in the brain utilising an alternate exon homologous to human exon 28.

CONCLUSION

Dogs can be used as a model organism to explore the function of the alternately spliced transcript of VPS13B in the brain. TNS in Border collies is the first animal model for Cohen syndrome and can be used to study the disease aetiology.

Primary immunodeficiencies of dogs and cats

Primary immunodeficiencies are congenital defects that affect formation or function of the immune system. Congenital immunodeficiency should be considered as a differential diagnosis for repeated infections in a young animal. Defects in the immune system may lead to complete or partial loss of immunity. Some animals with mild immunodeficiency can be managed with long-term antibiotic therapy.

Potential large animal models for gene therapy of human genetic diseases of immune and blood cell systems

Genetic mutations involving the cellular components of the hematopoietic system--red blood cells, white blood cells, and platelets--manifest clinically as anemia, infection, and bleeding. Although gene targeting has recapitulated many of these diseases in mice, these murine homologues are limited as translational models by their small size and brief life span as well as the fact that mutations induced by gene targeting do not always faithfully reflect the clinical manifestations of such mutations in humans. Many of these limitations can be overcome by identifying large animals with genetic diseases of the hematopoietic system corresponding to their human disease counterparts. In this article, we describe human diseases of the cellular components of the hematopoietic system that have counterparts in large animal species, in most cases carrying mutations in the same gene (CD18 in leukocyte adhesion deficiency) or genes in interacting proteins (DNA cross-link repair 1C protein and protein kinase, DNA-activated catalytic polypeptide in radiation-sensitive severe combined immunodeficiency). Furthermore, we describe the potential of these animal models to serve as disease-specific preclinical models for testing the efficacy and safety of clinical interventions such as hematopoietic stem cell transplantation or gene therapy before their use in humans with the corresponding disease.

Characterization of cDNA and genomic sequences encoding a canine chemokine receptor, CXCR4 and its ligand CXCL12

The interaction of chemokine receptor CXCR4 and its functional ligand CXCL12 plays a key role in bone marrow hematopoiesis, neuronal and cardiovascular development, and organization of the immune system. Despite the importance of the CXCL12-CXCR4 axis for regulating hematopoiesis, information on the canine CXCR4 and CXCL12 genes is insufficient. In this present study, we identified the canine counterparts of the CXCR4 and CXCL12 cDNAs and genes. The amino acid sequence encoding canine CXCR4 showed the structural characteristics of seven transmembrane domain G protein-coupled receptors and high homology with those of humans and other animals. Two isoforms, CXCL12 alpha and CXCL12 beta, were identified in dogs, as described in human and other animals. The gene structures for canine CXCR4 and CXCL12 were similar to those of other animals. The canine CXCL12 gene structure indicated that the transcripts of the isoforms arose from alternative mRNA splicing. A single nucleotide polymorphism (SNP) with synonymous substitution was observed in the exon of the canine CXCL12 gene. mRNAs encoding canine CXCR4 and CXCL12 were expressed widely and constitutively. Molecular homology and constitutive expression of CXCR4 and CXCL12 mRNAs in canine normal tissues suggests critical roles in hematopoiesis and trafficking of leukocytes, as shown in other animals.