Assignation of highly polymorphic markers on a canine purebred pedigree

Long- and short-haired Weimaraner dogs represent two populations of one breed

Weimaraners represent an old breed of hunting dogs. Today, two coat types are commonly distinguished, the more common short-hair (SH) and the long-hair (LH) variety, the latter having arisen from the SH Weimaraners. In order to analyze genetic variation in the coat varieties, we genotyped nine single nucleotide polymorphisms (SNPs) of the ABCA4 gene locus as well as six highly variable microsatellites scattered over the canine genome in the SH and LH populations. Three out of nine SNPs showed two alleles, allelic frequencies at two of these polymorphic sites differed significantly between SH and LH Weimaraners. Haplotype diversities for the three informative SNPs revealed higher estimates for the SH (0.515) than for the LH variety (0.364). In addition, two of six microsatellite markers showed significant differences in allelic frequencies between SH and LH Weimaraners. Unexpectedly, genetic diversities for all but one microsatellite were greater in LH than in SH Weimaraners. Similarly, the mean intra-individual genetic distance based on microsatellite markers was more pronounced in the LH population (0.62 for SH vs. 0.65 for LH) suggesting again closer genetic relationships among SH than LH Weimaraners. Taken together, the results of SNP analysis can be interpreted as reflections of early breed development whereas microsatellites mirror rather recent breeding strategies in the Weimaraner populations.

The keeshond defect in cardiac conotruncal development is oligogenic1

Earlier studies in the keeshond breed of dogs established that isolated conotruncal defects (CTDs) are a group of genetically and embryologically related cardiac malformations, including sub-clinical defects of the conal septum, conal ventricular septal defects, tetralogy of Fallot, and persistent truncus arteriosus. The same spectrum occurs in some human families. In both species, inheritance of non-syndromic CTDs is usually complex and multifactorial inheritance has been assumed. Previous studies in the keeshond suggested that susceptibility to CTD is an autosomal recessive trait, with alleles at modifying loci affecting severity. Here we report results of a genome-wide scan for CTD linked loci in a keeshond x beagle F1 backcross pedigree in which 46 of 101 offspring had CTDs. Two-point linkage analysis identified regions of suggestive linkage on each of three chromosomes CFA2, CFA9, and CFA15. No single locus accounted for segregation of CTDs in the pedigree, ruling out a single autosomal susceptibility locus. Multipoint analysis with Genehunter resulted in a corrected LOD score of 3.7 at the locus on CFA9 and supported linkage to the loci on CFA2 and CFA15 (LOD scores of 2.71 and 3.03). Genehunter Twolocus analysis suggested that CTD-predisposing alleles of these three loci are necessary, at least in pairs, to produce CTD. The canine CTD-linked chromosome regions are orthologous to human regions HSA5q11-13, HSA5q31, HSA17q11-24, and HSA4q31. We excluded from the linked regions in the dog, a number of genes known to have a role in the etiology of CTDs and predict that continuing studies will identify CTD-predisposing genes not previously recognized.

A proposed nomenclature for 15 canine-specific polymorphic STR loci for forensic purposes

We performed a population study on 15 polymorphic STR loci (FH2010, FH2079, PEZ2, VWF.X, FH2054, FH2087Ub, FH2611, WILMS-TF, PEZ12, PEZ15, PEZ6, FH2087Ua, ZUBECA4, ZUBECA6, FH2132) on 131 randomly selected dogs. Alleles were identified and grouped according to their estimated fragment length using fixed allelic bins encompassing one base-pair. The allele assignment was confirmed by sequence analysis of homozygote and cloned heterozygote alleles. In order to develop a uniform repeat-based nomenclature, extensive sequence analysis was performed on a selection of alleles from each STR locus. The proposed nomenclature refers to the internationally recognised recommendations for human-specific STR loci in forensic applications. The 15 canine-specific STR loci were grouped into 3 classes (simple STRs, compound STRs and complex/hypervariable STRs) according to their complexity and variability within the repeat structure. Finally, we evaluated the precision of fragment size estimation on a capillary electrophoresis platform and demonstrated reproducibility of fragment length estimation for single base-pair intermediate alleles.

The cnm locus, a canine homologue of human autosomal forms of centronuclear myopathy, maps to chromosome 2

Myotubular/centronuclear myopathies are a nosological group of hereditary disorders characterised by severe architectural and metabolic remodelling of skeletal muscle fibres. In most myofibres, nuclei are found at an abnormal central position within a halo devoid of myofibrillar proteins. The X-linked form (myotubular myopathy) is the most prevalent and severe form in human, leading to death during early postnatal life. Maturation of fibres is not completed and fibres resemble myotubes. Linkage analysis in human has helped to identify MTM1 as the morbid gene. MTM1 encodes myotubularin, a dual protein phosphatase. In families in which myotubular myopathy segregates, detected mutations in MTM1 abolish the specific phosphatase activity targeting the second messenger phosphatidylinositol 3-phosphate. Autosomal forms (centronuclear) have a later onset and are often compatible with life. At birth, fibres are normally constituted but progressively follow remodelling with a secondary centralisation of nuclei. Their prevalence is low; hence, no linkage data can be performed and no molecular aetiology is known. In the Labrador Retriever, a spontaneous disorder strikingly mimics the clinical evolution of the human centronuclear myopathy. We have established a canine pedigree and show that the disorder segregates as an autosomal recessive trait in that pedigree. We have further mapped the dog locus to a region on chromosome 2 that is orthologous to human chromosome 10p. To date, no human MTM1 gene member has been mapped to this genetic region. This report thus describes the first spontaneous mammalian model of centronuclear myopathy and defines a new locus for this group of diseases.

Linkage mapping of the primary disease locus for collie eye anomaly

Collie eye anomaly (cea) is a hereditary ocular disorder affecting development of the choroid and sclera segregating in several breeds of dog, including rough, smooth, and Border collies and Australian shepherds. The disease is reminiscent of the choroidal hypoplasia phenotype observed in humans in conjunction with craniofacial or renal abnormalities. In dogs, however, the clinical phenotype can vary significantly; many dogs exhibit no obvious clinical consequences and retain apparently normal vision throughout life, while severely affected animals develop secondary retinal detachment, intraocular hemorrhage, and blindness. We report genetic studies establishing that the primary cea phenotype, choroidal hypoplasia, segregates as an autosomal recessive trait with nearly 100% penetrance. We further report linkage mapping of the primary cea locus to a 3.9-cM region of canine chromosome 37 (LOD = 22.17 at theta = 0.076), in a region corresponding to human chromosome 2q35. These results suggest the presence of a developmental regulatory gene important in ocular embryogenesis, with potential implications for other disorders of ocular vascularization.