Association of canine anal furunculosis with TNFA is secondary to linkage disequilibrium with DLA‐DRB1*

Abstract

Anal furunculosis (AF) is a chronic inflammatory disease of perianal tissues that particularly affects German Shepherd dogs (GSD). An immune-mediated aetiopathogenesis is suggested by T-cell infiltration, upregulated cytokine gene expression, clinical response to ciclosporin therapy and a strong genetic association with the DLA-DRB1*00101 allele. Given the close proximity of TNFA and DLA-DRB1 in the canine major histocompatibility complex (MHC), together with the strong linkage disequilibrium (LD) observed across this region, the primary disease association could be with either locus. We have investigated whether there may be an association of AF with TNFA gene polymorphism in GSDs. Cohorts of AF-affected and AF-unaffected GSDs of known dog leucocyte antigen (DLA) class II profile were genotyped for 10 single nucleotide polymorphisms (SNPs) in the canine TNFA locus using Sequenom iPLEX technology. Seven discrete TNFA haplotypes were identified in GSDs for combinations of these SNPs. TNFA haplotype frequencies were compared in cases and controls. The TNFA haplotype 3 (ATCGTTACGG), was at significantly increased frequency in cases (29% vs 15%, OR 2.5, 95% CI 1.4-4.8; P = 0.003). All seven discrete TNFA SNP haplotypes were examined for their association with DLA-DRB1/DQA1/DQB1 established haplotypes. TNFA haplotype 3 was preferentially associated with both DLA-DRB1*00101(3A)- and DLA-DRB1*00102(3B)-positive haplotypes. The DLA-DRB1* 00101/TNFA-3A haplotype was significantly associated with AF (19.3% vs 5.8%; OR 3.7, 95% CI: 1.5-8.9; P = 0.003), whereas the DLA-DRB1*00102/TNFA-3B haplotype was not (P = NS). These findings suggest that susceptibility to AF in GSDs is primarily associated with DLA-DRB1*00101 and any association with the TNFA locus is secondary and is likely to be because of LD.

Expanded dog leukocyte antigen (DLA) single nucleotide polymorphism (SNP) genotyping reveals spurious class II associations

“…A protective allele, DLA-DRB1*01201, was also identified (OR 0.156; 95% CI 0.04–0.52; P = 0.002) (Table 1). These values are as high or higher than previously published class II associations (Kennedy et al, 2007c; Catchpole et al, 2008; Barnes et al, 2009). None of the seven other exon 2 alleles found in the Weimaraner sample set were associated with HOD.…”

“…So far, no mutations that can explain a mechanism for increased susceptibility have been identified in the classic MHC class II genes in humans (Holmdahl, 2000; Coenen and Gregersen, 2009; Ramagopalan and Ebers, 2009) or dogs (Kennedy et al, 2006a and b, 2007c, 2008; Barnes et al, 2009). …”

Necrotizing meningoencephalitis of Pug Dogs associates with dog leukocyte antigen class II and resembles acute variant forms of multiple sclerosis

“…N ME of Pug Dogs is not the first disease of purebred dogs to be associated with DLA class II genes. A Vogt‐Koyanagi‐Harada‐like syndrome of the Akita is associated with DLA class II genes (29), as is autoimmune hemolytic anemia, immune arthritis, and hypothyroidism in several breeds (30–32), type I diabetes mellitus in Samoyed dogs, Cairn, and Tibetan Terriers (33), anal furunculosis of German Shepherd dogs (34), and a systemic lupus erythematosus‐related complex of Nova Scotia Tollers (35). This supports the hypothesis of Svejgaard (36) that many autoimmune disorders of humans, and now dogs, may be major histocompatibility (MHC) associated.…”

Genome-wide association studies for multiple diseases of the German Shepherd Dog

“…DLA-88 is the most highly polymorphic class I locus of the DLA complex. DLA class II loci are associated with several immune-related disorders, including diabetes mellitus, anal furunculosis, hypoadrenocorticism, and necrotizing meningoencephalitis (Barnes et al 2009; Greer et al 2010; Hughes et al 2010; Kennedy et al 2006). Canine systemic lupus erythematosus, a classic autoimmune disease, is also reported to be associated with alleles of the DLA class II loci, and GWAS revealed five additional associated loci (Wilbe et al 2009, 2010).…”