The canine sarcoglycan delta gene: BAC clone contig assembly, chromosome assignment and interrogation as a candidate gene for dilated cardiomyopathy in Dobermann dogs

Functional Consequences of PDK4 Deficiency in Doberman Pinscher Fibroblasts

A splice site mutation in the canine pyruvate dehydrogenase kinase 4 (PDK4) gene has been shown to be associated with the development of dilated cardiomyopathy (DCM) in Doberman Pinchers (DPs). Subsequent studies have successfully demonstrated the use of dermal fibroblasts isolated from DPs as models for PDK4 deficiency and have shown activation of the intrinsic (mitochondrial mediated) apoptosis pathway in these cells under starvation conditions. For this study, we sought to further explore the functional consequences of PDK4 deficiency in DP fibroblasts representing PDK4^wt/wt, PDK4^wt/del, and PDK4^del/del genotypes. Our results show that starvation conditions cause increased perinuclear localization of mitochondria and decreased cell proliferation, altered expression levels of pyruvate dehydrogenase phosphatase (PDP) and pyruvate dehydrogenase (PDH), dramatically increased PDH activity, and an impaired response to mitochondrial stress in affected cells. In sum, these results show the broad impact of PDK4 deficiency and reveal mechanistic pathways used by these cells in an attempt to compensate for the condition. Our data help to elucidate the mechanisms at play in this extremely prevalent DP disorder and provide further support demonstrating the general importance of metabolic flexibility in cell health.

Genetics of Human and Canine Dilated Cardiomyopathy

Cardiovascular disease is a leading cause of death in both humans and dogs. Dilated cardiomyopathy (DCM) accounts for a large number of these cases, reported to be the third most common form of cardiac disease in humans and the second most common in dogs. In human studies of DCM there are more than 50 genetic loci associated with the disease. Despite canine DCM having similar disease progression to human DCM studies into the genetic basis of canine DCM lag far behind those of human DCM. In this review the aetiology, epidemiology, and clinical characteristics of canine DCM are examined, along with highlighting possible different subtypes of canine DCM and their potential relevance to human DCM. Finally the current position of genetic research into canine and human DCM, including the genetic loci, is identified and the reasons many studies may have failed to find a genetic association with canine DCM are reviewed.

Muscular dystrophy due to a sarcoglycan deficiency in a female Dobermann dog

A four-month-old female Dobermann presented with myalgia, dysphagia, progressive weakness and loss of body condition. Diagnostic evaluation at nine months of age revealed markedly elevated serum creatine kinase activity, electromyographic abnormalities and histological evidence of chronic-active muscle necrosis. Imaging confirmed dysphagia and aspiration pneumonia. Muscular dystrophy was suspected and immunohistochemical staining of muscle cryosections demonstrated reduced sarcoglycans. Treatment consisted of gastrostomy, and over the next 5 months the dog gained weight, despite continued loss of muscle mass. The dog died at 14 months of age after developing clinical signs of aspiration pneumonia. To the authors' knowledge, this is the first report of muscular dystrophy in a Dobermann and only the second detailed report of a canine sarcoglycanopathy. Supportive care resulted in an acceptable quality of life for 10 months after clinical signs were first observed.

White blood cell transcriptome correlates with renal function in acute heart failure

It is notoriously difficult to classify patients with acute heart failure (AHF) because of variations in clinical presentation, different etiologies, the impact of comorbidities, and variable prognoses. In this study, we used DNA whole-genome microarrays to classify 24 patients with AHF based on the transcriptome of their peripheral blood nuclear cells. The main purpose was to verify whether any transcriptomic sub-clusters had clinical correlations. We identified two distinct groups of transcriptomic profiles that correlated with normal (1.125 mg/dL) and increased (1.783 mg/dL) mean blood creatinine concentrations. These two subgroups of patients (n = 12) differed in the expression of more than 6000 genes and 108 signaling pathways. The most significant regulated signaling pathway was the aldosterone-regulated sodium reabsorption pathway and the most significant regulated genes included the angiotensin-converting enzyme gene. This suggests that kidney impairment in patients with AHF is related to dysregulation of the renin-angiotensin-aldosterone system. The interesting findings of our study were the significant differences in expression of genes belonging to the aldosterone-regulated signaling pathway: Na⁺/K⁺ transporting ATPase and NEDD4L (neuronal precursor cell expressed developmentally down-regulated 4-like) between patients with and without renal dysfunction. Future studies of blood-cell transcriptomic profiles in patients with AHF will provide further insights into the molecular pathogenesis of this cardiorenal disorder.

Multiple Loci are associated with dilated cardiomyopathy in Irish wolfhounds

Dilated cardiomyopathy (DCM) is a highly prevalent and often lethal disease in Irish wolfhounds. Complex segregation analysis indicated different loci involved in pathogenesis. Linear fixed and mixed models were used for the genome-wide association study. Using 106 DCM cases and 84 controls we identified one SNP significantly associated with DCM on CFA37 and five SNPs suggestively associated with DCM on CFA1, 10, 15, 21 and 17. On CFA37 MOGAT1 and ACSL3 two enzymes of the lipid metabolism were located near the identified SNP.

A splice site mutation in a gene encoding for PDK4, a mitochondrial protein, is associated with the development of dilated cardiomyopathy in the Doberman pinscher

Familial dilated cardiomyopathy is a primary myocardial disease that can result in the development of congestive heart failure and sudden cardiac death. Spontaneous animal models of familial dilated cardiomyopathy exist and the Doberman pinscher dog is one of the most commonly reported canine breeds. The objective of this study was to evaluate familial dilated cardiomyopathy in the Doberman pinscher dog using a genome-wide association study for a genetic alteration(s) associated with the development of this disease in this canine model. Genome-wide association analysis identified an area of statistical significance on canine chromosome 14 (p(raw) = 9.999e-05 corrected for genome-wide significance), fine-mapping of additional SNPs flanking this region localized a signal to 23,774,190-23,781,919 (p = 0.001) and DNA sequencing identified a 16-base pair deletion in the 5' donor splice site of intron 10 of the pyruvate dehydrogenase kinase 4 gene in affected dogs (p < 0.0001). Electron microscopy of myocardium from affected dogs demonstrated disorganization of the Z line, mild to moderate T tubule and sarcoplasmic reticulum dilation, marked pleomorphic mitochondrial alterations with megamitochondria, scattered mitochondria with whorling and vacuolization and mild aggregates of lipofuscin granules. In conclusion, we report the identification of a splice site deletion in the PDK4 gene that is associated with the development of familial dilated cardiomyopathy in the Doberman pinscher dog.

Genomic and genetic aspects of heart failure in dogs - a review

The most common causes of heart failure in dogs are valvular disease, predominantly endocardiosis, and myocardial disease, predominantly dilated cardiomyopathy. They are related to changes in the expression of several genes in the heart muscle and in peripheral blood nuclear cells which could be considered as prognostic or diagnostic markers of heart disease in dogs. Since many human genetic markers of heart failure have turned out to be useless in dogs, the screening for genomic markers of canine heart failure could give more insight into the molecular pathology of these diseases and aid the development of new treatment strategies.

A contracted DNA repeat in LHX3 intron 5 is associated with aberrant splicing and pituitary dwarfism in German shepherd dogs

Dwarfism in German shepherd dogs is due to combined pituitary hormone deficiency of unknown genetic cause. We localized the recessively inherited defect by a genome wide approach to a region on chromosome 9 with a lod score of 9.8. The region contains LHX3, which codes for a transcription factor essential for pituitary development. Dwarfs have a deletion of one of six 7 bp repeats in intron 5 of LHX3, reducing the intron size to 68 bp. One dwarf was compound heterozygous for the deletion and an insertion of an asparagine residue in the DNA-binding homeodomain of LHX3, suggesting involvement of the gene in the disorder. An exon trapping assay indicated that the shortened intron is not spliced efficiently, probably because it is too small. We applied bisulfite conversion of cytosine to uracil in RNA followed by RT-PCR to analyze the splicing products. The aberrantly spliced RNA molecules resulted from either skipping of exon 5 or retention of intron 5. The same splicing defects were observed in cDNA derived from the pituitary of dwarfs. A survey of similarly mutated introns suggests that there is a minimal distance requirement between the splice donor and branch site of 50 nucleotides. In conclusion, a contraction of a DNA repeat in intron 5 of canine LHX3 leads to deficient splicing and is associated with pituitary dwarfism.

Evaluation of 10 genes encoding cardiac proteins in Doberman Pinschers with dilated cardiomyopathy

OBJECTIVE

To identify a causative mutation for dilated cardiomyopathy (DCM) in Doberman Pinschers by sequencing the coding regions of 10 cardiac genes known to be associated with familial DCM in humans.

ANIMALS

5 Doberman Pinschers with DCM and congestive heart failure and 5 control mixed-breed dogs that were euthanized or died.

PROCEDURES

RNA was extracted from frozen ventricular myocardial samples from each dog, and first-strand cDNA was synthesized via reverse transcription, followed by PCR amplification with gene-specific primers. Ten cardiac genes were analyzed: cardiac actin, α-actinin, α-tropomyosin, β-myosin heavy chain, metavinculin, muscle LIM protein, myosinbinding protein C, tafazzin, titin-cap (telethonin), and troponin T. Sequences for DCM-affected and control dogs and the published canine genome were compared.

RESULTS

None of the coding sequences yielded a common causative mutation among all Doberman Pinscher samples. However, 3 variants were identified in the α-actinin gene in the DCM-affected Doberman Pinschers. One of these variants, identified in 2 of the 5 Doberman Pinschers, resulted in an amino acid change in the rod-forming triple coiled-coil domain.

CONCLUSIONS AND CLINICAL RELEVANCE

Mutations in the coding regions of several genes associated with DCM in humans did not appear to consistently account for DCM in Doberman Pinschers. However, an α-actinin variant was detected in some Doberman Pinschers that may contribute to the development of DCM given its potential effect on the structure of this protein. Investigation of additional candidate gene coding and noncoding regions and further evaluation of the role of α-actinin in development of DCM in Doberman Pinschers are warranted.

A locus on chromosome 5 is associated with dilated cardiomyopathy in Doberman Pinschers

Dilated cardiomyopathy (DCM) is a heterogeneous group of heart diseases with a strong genetic background. Currently, many human DCM cases exist where no causative mutation can be identified. DCM also occurs with high prevalence in several large dog breeds. In the Doberman Pinscher a specific DCM form characterized by arrhythmias and/or echocardiographic changes has been intensively studied by veterinary cardiologists. We performed a genome-wide association study in Doberman Pinschers. Using 71 cases and 70 controls collected in Germany we identified a genome-wide significant association to DCM on chromosome 5. We validated the association in an independent cohort collected in the United Kingdom. There is no known DCM candidate gene under the association signal. Therefore, DCM in Doberman Pinschers offers the chance of identifying a novel DCM gene that might also be relevant for human health.

Evaluation of the titin-cap gene (TCAP) as candidate for dilated cardiomyopathy in Irish wolfhounds

Dilated cardiomyopathy (DCM) is a myocardial disorder characterized by left ventricular dilatation and impaired systolic contraction. Irish wolfhounds (IW) and other large breed dogs are most commonly disposed to DCM. We analyzed the titin-cap (TCAP, telethonin) gene as candidate for DCM. Genomic DNA was analyzed in eight DCM affected and five DCM-free IWs. cDNA was sequenced in one DCM-affected IW and two unaffected dogs, one Tibetan terrier and one Dachshund. Compared to the Boxer reference sequence, one sequence difference was identified in the 3'UTR and two in the intron sequence. In the IWs the sequences were monomorphic. In order to rule out a breed-specific haplotype that predisposes to DCM, the polymorphisms were genotyped in 24 Elo dogs, a breed mix established from nine different breeds. The analysis showed that the mutations were not restricted to IW. Moreover, 80% of the Elos were homozygous for the IW haplotype. We conclude that TCAP can most likely be eliminated as cause for DCM in IWs.

Canine cytogenetics--from band to basepair

Humans and dogs have coexisted for thousands of years, during which time we have developed a unique bond, centered on companionship. Along the way, we have developed purebred dog breeds in a manner that has resulted unfortunately in many of them being affected by serious genetic disorders, including cancers. With serendipity and irony the unique genetic architecture of the 21st century genome of Man's best friend may ultimately provide many of the keys to unlock some of nature's most intriguing biological puzzles. Canine cytogenetics has advanced significantly over the past 10 years, spurred on largely by the surge of interest in the dog as a biomedical model for genetic disease and the availability of advanced genomics resources. As such the role of canine cytogenetics has moved rapidly from one that served initially to define the gross genomic organization of the canine genome and provide a reliable means to determine the chromosomal location of individual genes, to one that enabled the assembled sequence of the canine genome to be anchored to the karyotype. Canine cytogenetics now presents the biomedical research community with a means to assist in our search for a greater understanding of how genome architectures altered during speciation and in our search for genes associated with cancers that affect both dogs and humans. The cytogenetics 'toolbox' for the dog is now loaded. This review aims to provide a summary of some of the recent advancements in canine cytogenetics.

Canine candidate genes for dilated cardiomyopathy: annotation of and polymorphic markers for 14 genes

Background

Dilated cardiomyopathy is a myocardial disease occurring in humans and domestic animals and is characterized by dilatation of the left ventricle, reduced systolic function and increased sphericity of the left ventricle. Dilated cardiomyopathy has been observed in several, mostly large and giant, dog breeds, such as the Dobermann and the Great Dane. A number of genes have been identified, which are associated with dilated cardiomyopathy in the human, mouse and hamster. These genes mainly encode structural proteins of the cardiac myocyte.

Results

We present the annotation of, and marker development for, 14 of these genes of the dog genome, i.e. α-cardiac actin, caveolin 1, cysteine-rich protein 3, desmin, lamin A/C, LIM-domain binding factor 3, myosin heavy polypeptide 7, phospholamban, sarcoglycan δ, titin cap, α-tropomyosin, troponin I, troponin T and vinculin. A total of 33 Single Nucleotide Polymorphisms were identified for these canine genes and 11 polymorphic microsatellite repeats were developed.

Conclusion

The presented polymorphisms provide a tool to investigate the role of the corresponding genes in canine Dilated Cardiomyopathy by linkage analysis or association studies.

Finding cardiovascular disease genes in the dog

Recent advances in canine genomics are changing the landscape of veterinary biology, and by default, veterinary medicine. No longer are clinicians locked into traditional methods of diagnoses and therapy. Rather, major advances in canine genetics and genomics from the past five years are now changing the way the veterinarian of the 21st century practices medicine. First, the availability of a dense genome map gives canine genetics a much-needed foothold in comparative medicine, allowing advances made in human and mouse genetics to be applied to companion animals. Second, the recently released 7.5x whole genome sequence of the dog is facilitating the identification of hereditary disease genes. Finally, development of genetic tools for rapid screening of families and populations at risk for inherited disease means that the cost of identifying and testing for disease loci will significantly decrease in coming years. Out of these advances will come major changes in companion animal diagnostics and therapy. Clinicians will be able to offer their clients genetic testing and counseling for a myriad of disorders. In this review we summarize recent findings in canine genomics and discuss their application to the study of canine cardiac health.