Discovery of a novel pathway for an SLE-related disease complex in the canine breed Nova Scotia duck tolling retriever
Abstract: The dog is an excellent model to study inherited complex diseases, due to its unique population history and haplotype structure. In this thesis, dogs from the breed Nova Scotia duck tolling retriever (NSDTR) have been used as a model for defining the genetic factors controlling a systemic lupus erythematosus (SLE)-related disorder called immune-mediated rheumatic disease (IMRD) and a steroid responsive meningitis-arteritis (SRMA). IMRD is characterized by stiffness, mainly after resting, and pain from several joints of extremities and/or muscle pain. The majority of the affected dogs show anti-nuclear antibody (ANA)-positivity that can be divided either into a speckled (ANAS) or homogenous (ANAH) staining pattern. Dogs affected by SRMA display severe neck pain, fever and stiffness and an increased infiltration of immune cells in cerebrospinal fluid in the acute phase of disease. SRMA dogs show a negative ANA result. We performed a candidate gene study to investigate if dog leukocyte antigen (DLA) class II is associated with the canine SLE-related disease. An increased risk for ANAS dogs was observed for a homozygous risk haplotype and a general homozygosity at DLA class II gives ANAH dogs an increased risk for developing disease. Genome-wide association mapping identified additional susceptibility loci for the SLE-related disease on canine chromosomes (CFA) 3, 8, 11, 24 and 32. Further analysis revealed that most ANAS dogs homozygous for the DLA risk haplotype also have the genetic risk factors at CFA 11 and 32. Re-sequencing of the five associated regions was performed to identify specific genes and genetic variants involved in the disease. Expression studies of the candidate genes for ANAS dogs revealed that the PTPN3 (CFA 11) gene is downregulated and that DDIT4L and BANK1 (CFA 32) is upregulated in dogs with the risk haplotype. The identified genes may be important in T-cells, B-cells and possibly macrophages. This thesis describes the first successful mapping of a complex trait in the dog and shows that MHC class II together with two other identified genetic risk factors contribute to development of systemic autoimmune disease.
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