Dogs suffer from many serious and sometimes life threatening genetic diseases of unknown genetic cause. This thesis investigated the genetic cause/s of two inherited diseases in dogs. Bull Terrier Polycystic Kidney Disease (BTPKD) is an autosomal dominant renal disease with an unknown genetic cause. Primary Lens Luxation (PLL) is an inherited ocular disease affecting many breeds of dogs, with a recently identified causative mutation, primarily found in Terrier breeds, in the canine ADAMTS17 orthologue. However, the inheritance of PLL, especially in breeds such as Miniature Bull Terriers (MBTs) and Tenterfield Terriers (TTs) is not completely understood, and other genetic loci or environmental factors may contribute to the development of clinical PLL in these breeds. Thus, there are 2 aims of this study: firstly, to investigate the genetic cause of BTPKD, how this mutation/s causes disease, and to develop a molecular diagnostic test. The thesis also had a second aim: to investigate the mode of inheritance and penetrance of PLL in MBTs and TTs, and the possible involvement of multiple genetic loci and environmental factors in this disease development.
A key finding of this thesis was to demonstrate that BTPKD is associated with a non-synonymous G>A transition mutation in exon 29 of canine Pkd1 orthologue. A TaqMan® SNP Genotyping Assay was designed to detect this mutation. Diagnosis test utilizing this mutation specific assay could reduce disease transmission within the breed by allowing diagnosis of disease in young animals prior to breeding. Protein expression studies to investigate the effects of the mutation on the structure and function of the encoded protein were unsuccessful. The primary reason may have been due to the toxicity of the protein for the E. coli strain used to clone the gene, thus preventing expression of the protein. Despite several strategies to overcome this problem no protein could be produced for further analysis. The mechanism causing toxicity for the bacterium is unclear.
This thesis also found that the PLL associated ADAMTS17 mutation was an old mutation which had a dose and age dependent effect on the risk of PLL in MBTs and TTs, and best fitted an additive inheritance model. The ADAMTS17 mutation was also found to be associated with abnormal foot and nail shape and pedal hyperkeratosis, and persistent papillary membranes in the population of MBTs. A genome wide association study to investigate possible involvement of other loci in the PLL phenotype in populations of MBTs showed that two loci with potentially enhancing effects on the ADAMST17 mutation were associated with PLL. Besides that associated with the ADAMTS17 mutation (P = 2.2e-05), the highest association peaks were at locus 62.2 Mb on chromosome 15 (P = 7.8e-05) and the region between 30 Mb and 32.5 Mb on chromosome 1 (P =9.3e-05). Candidate genes in the two regions of interest included CPE on chromosome 15 and CTGF on chromosome 1.
In conclusion, this study found a BTPKD associated mutation, and a diagnostic test was developed to identify BTPKD affected animals prior to sale or breeding which in turn can reduce the incidence of the disease. This study also contributed towards increased understanding of inheritance and genetic causes of PLL in MBTs and TTs. Hence, the findings from this study have led to a better understanding of the pathogenesis of these diseases. These findings may also be useful for understanding homologous genetic diseases in other species, including humans.