P. A. J. Leegwater

Dilated cardiomyopathy (DCM) is a disease of the myocardium, which causes heart failure and premature death. It has been described in humans and several domestic animals. In the Newfoundland dog, DCM is an autosomal dominant disease with late onset and reduced penetrance. We analyzed 15 candidate genes for their involvement in DCM in the Newfoundland dog. Polymorphic microsatellite markers and single Nucleotide Polymorphisms were genotyped in 4 families of Newfoundland dogs segregating dilated cardiomyopathy for the genes encoding a-cardiac actin (ACTC ), caveolin (CAVI ), cysteine-rich protein 3 (CSRP3 ), LIM-domain binding factor 3 (LDB3 ), desmin (DES ), lamin A/C (LMNA ), myosin heavy polypeptide 7 (MYH7 ), delta-sarcoglycan (SGCD ), troponin I (TNNTI3 ), troponin T (TNNT2 ), alpha-tropomyosin (TPMI ), titin (TTN ) and vinculin (VCL ). A Logarithm of the odds (LOD) score of less than � 2.0 in 2-point linkage analysis indicated exclusion of all but 2 genes, encoding CSRP3 and DES. A (LOD) score between � 1.5 and � 2.0 for CSRP3 and DES makes these genes unlikely causes of DCM in this dog breed. For the phospholamban (PLN ) and titin cap (TTN ) genes, a direct mutation screening approach was used. DNA sequence analysis of all exons showed no evidence that these genes are involved in DCM in the Newfoundland dog.

New techniques allow fast genotyping of large numbers of single-nucleotide polymorphisms (SNPs) of the genome. These techniques are used to map disorders with complex inheritance patterns and require large study groups. Linkage analysis of monogenetic traits exploits close family relationships between relatively small numbers of cases and controls. Linkage studies are typically performed with a set of microsatellite markers spaced at 10 cM. We were interested to test whether SNP typing could be applied in genome-wide linkage analysis because of the speed of the procedure. White spotting in Boxer dogs was chosen as a model because it is a semidominant trait, allowing the assignment of locus genotypes to each phenotyped dog. A set of just more than 1500 SNPs were typed in 5 families with heterozygous parents and offspring that included 11 white, 6 brown, and 19 spotted dogs. Multipoint linkage analysis was performed and a LOD score of 12.1 was obtained on canine chromosome 20. The CFA20 region was the only region with a positive LOD score. The gene MITF, coding for a transcription factor implicated in Waardenburg syndrome in humans, is located in the region close to a SNP that is in apparent linkage disequilibrium with the white spotting locus. Thus, MITF is a likely candidate for involvement in white spotting in boxers. We conclude that SNPs, spaced at an average distance of 1.6 Mb, are highly informative in linkage analysis of monogenic traits and are a powerful alternative to microsatellite markers.