Severity of Mitral Valve Degeneration Is Associated with Chromosome 15 Loci in Whippet Dogs

Mitral valve transcriptome analysis in thirty-four age-matched Cavalier King Charles Spaniels with or without congestive heart failure caused by myxomatous mitral valve disease

We here report the results of a mitral valve transcriptome study designed to identify genes and molecular pathways involved in development of congestive heart failure (CHF) following myxomatous mitral valve disease (MMVD) in dogs. The study is focused on a cohort of elderly age-matched dogs (n = 34, age ~ 10 years) from a single breed-Cavalier King Charles Spaniels (CKCS)-with a high incidence of MMVD. The cohort comprises 19 dogs (10♀, 9♂) without MMVD-associated CHF, and 15 dogs (6♀, 9♂) with CHF caused by MMVD; i.e., we compare gene expression in breed and age-matched groups of dogs, which only differ with respect to CHF status. We identify 56 genes, which are differentially expressed between the two groups. In this list of genes, we confirm an enrichment of genes related to the TNFβ-signaling pathway, extracellular matrix organization, vascular development, and endothelium damage, which also have been identified in previous studies. However, the genes with the greatest difference in expression between the two groups are CNTN3 and MYH1. Both genes encode proteins, which are predicted to have an effect on the contractile activity of myocardial cells, which in turn may have an effect on valvular performance and hemodynamics across the mitral valve. This may result in shear forces with impact on MMVD progression.

Echocardiographic values for normal conditioned and unconditioned North American whippets

BACKGROUND

Echocardiographic reference intervals have not been reported for North American whippets, or for whippets that have undergone pet-level athletic training.

OBJECTIVES

To develop normal echocardiographic reference intervals for North American whippets and investigate differences in echocardiographic parameters based on athletic conditioning in pet whippets engaged in competitive sports.

ANIMALS

One-hundred healthy North American whippets.

METHODS

Dogs were examined at national shows between 2005 and 2009. Echocardiographic reference intervals were constructed and the effect of athletic conditioning on parameters of structure and function was assessed.

RESULTS

Two dimensional, M-mode, Doppler and tissue Doppler reference ranges for healthy North American whippets are presented. Measures of left ventricular (LV) chamber diameter were larger in conditioned whippets (N = 25) and remained significantly larger than in unconditioned whippets (N = 16) when normalized for weight using allometric equations. Calculated LV mass was higher in conditioned dogs than in unconditioned dogs, and this difference persisted when LV mass was normalized by weight. Mitral E velocity was higher in conditioned dogs than in unconditioned dogs, whereas E/A and measures related to systolic function were not different.

CONCLUSIONS AND CLINICAL IMPORTANCE

Pet whippets in peak athletic condition have larger hearts than do less conditioned whippets, but measures of systolic function are similar. Whippet pet athletes may show eccentric LV hypertrophy at peak condition. Normal values for cardiac size and function in North American whippets might be considered abnormal if population-specific whippet reference intervals are not used in analysis.

Follistatin-like 1 and its paralogs in heart development and cardiovascular disease

Cardiovascular diseases (CVDs) are a group of disorders affecting the heart and blood vessels and a leading cause of death worldwide. Thus, there is a need to identify new cardiokines that may protect the heart from damage as reported in GBD 2017 Causes of Death Collaborators (2018) (The Lancet 392:1736-1788). Follistatin-like 1 (FSTL1) is a cardiokine that is highly expressed in the heart and released to the serum after cardiac injury where it is associated with CVD and predicts poor outcome. The action of FSTL1 likely depends not only on the tissue source but also post-translation modifications that are target tissue- and cell-specific. Animal studies examining the effect of FSTL1 in various models of heart disease have exploded over the past 15 years and primarily report a protective effect spanning from inhibiting inflammation via transforming growth factor, preventing remodeling and fibrosis to promoting angiogenesis and hypertrophy. A better understanding of FSTL1 and its homologs is needed to determine whether this protein could be a useful novel biomarker to predict poor outcome and death and whether it has therapeutic potential. The aim of this review is to provide a comprehensive description of the literature for this family of proteins in order to better understand their role in normal physiology and CVD.

Validation of a Chromosome 14 Risk Haplotype for Idiopathic Epilepsy in the Belgian Shepherd Dog Found to Be Associated with an Insertion in the RAPGEF5 Gene

An idiopathic epilepsy (IE) risk haplotype on canine chromosome (CFA) 14 has been reported to interact with the CFA37 common risk haplotype in the Belgian shepherd (BS). Additional IE cases and control dogs were genotyped for the risk haplotypes to validate these previous findings. In the new cohort, the interaction between the two regions significantly elevated IE risk. When the haplotypes were analyzed individually, particular haplotypes on both CFA14 (ACTG) and 37 (GG) were associated with elevated IE risk, though only the CFA37 AA was significantly associated (p < 0.003) with reduced risk in the new cohort. However, the CFA14 ACTG risk was statistically significant when the new and previous cohort data were combined. The frequency of the ACTG haplotype was four-fold higher in BS dogs than in other breeds. Whole genome sequence analysis revealed that a 3-base pair predicted disruptive insertion in the RAPGEF5 gene, which is adjacent to the CFA14 risk haplotype. RAPGEF5 is involved in the Wnt-β-catenin signaling pathway that is crucial for normal brain function. Although this risk variant does not fully predict the likelihood of a BS developing IE, the association with a variant in a candidate gene may provide insight into the genetic control of canine IE.

Influence of Morphometry on Echocardiographic Measurements in Cavalier King Charles Spaniels: An Inverse Probability Weighting Analysis

The development and progression of myxomatous mitral valve disease (MMVD) in Cavalier King Charles Spaniels (CKCS) are difficult to predict. Thus, the identification of dogs with a morphotype associated with more severe mitral disease at a young age is desirable. The aims of this study were to: (1) describe the physical, morphometric, and echocardiographic features of class B1 MMVD-affected Cavalier King Charles Spaniels (CKCS) according to the American College of Veterinary Internal Medicine (ACVIM) guidelines; (2) evaluate the influence of morphometric physical measurements on murmur intensity, mitral valve prolapse (MVP), regurgitant jet size, and indexed mitral valve and annulus measurements. Fifty-two MMVD-affected CKCS were included in the ACVIM class B1. This is a prospective clinical cross-sectional study. Morphometric measurements, which included the body, thorax, and head sizes of each dog, were investigated to establish the association with heart murmur intensity, valvular and annular echocardiographic measurements, MVP, and regurgitant jet size, using inverse probability weighting (IPW) analyses to adjust for confounding. The IPW analyses showed that when the head length and nose length decreased, dogs had a more severe regurgitant jet size. Furthermore, subjects with a more pronounced head stop angle had thicker anterior mitral valve leaflets. A brachycephalic morphotype, as seen in dogs similar to the King Charles Spaniel breed in terms of cephalic morphology, is associated with a more severe regurgitant jet size and with valvular characteristics that are related to the most severe forms of MMVD.

Genetics of canine myxomatous mitral valve disease

Myxomatous mitral valve disease (MMVD) is the most common heart disease and cause of cardiac death in domestic dogs. MMVD is characterised by slow progressive myxomatous degeneration from the tips of the mitral valves onwards with subsequent mitral valve regurgitation, and left atrial and ventricular dilatation. Although the disease usually has a long asymptomatic period, in dogs with severe disease, mortality is typically secondary to left-sided congestive heart failure. Although it is not uncommon for dogs to survive long enough in the asymptomatic period to die from unrelated causes; a proportion of dogs rapidly advance into congestive heart failure. Heightened prevalence in certain breeds, such as the Cavalier King Charles Spaniel, has indicated that MMVD is under a genetic influence. The genetic characterisation of the factors that underlie the difference in progression of disease is of strong interest to those concerned with dog longevity and welfare. Advanced genomic technologies have the potential to provide information that may impact treatment, prevalence, or severity of MMVD through the elucidation of pathogenic mechanisms and the detection of predisposing genetic loci of major effect. Here we describe briefly the clinical nature of the disorder and consider the physiological mechanisms that might impact its occurrence in the domestic dog. Using results from comparative genomics we suggest possible genetic approaches for identifying genetic risk factors within breeds. The Cavalier King Charles Spaniel breed represents a robust resource for uncovering the genetic basis of MMVD.

A Genomic Study of Myxomatous Mitral Valve Disease in Cavalier King Charles Spaniels

Cavalier King Charles spaniels (CKCSs) show the earliest onset and the highest incidence of myxomatous mitral valve disease (MMVD). Previous studies have suggested a polygenic inheritance of the disease in this breed and revealed an association with regions on canine chromosomes 13 and 14. Following clinical and echocardiographic examinations, 33 not-directly-related CKCSs were selected and classified as cases (n = 16) if MMVD was present before 5 years of age or as controls (n = 17) if no or very mild MMVD was present after 5 years of age. DNA was extracted from whole blood and genotyped with a Canine 230K SNP BeadChip instrument. Cases and controls were compared with three complementary genomic analyses (Wright's fixation index-F_ST, cross-population extended haplotype homozygosity-XP-EHH, and runs of homozygosity-ROH) to identify differences in terms of heterozygosity and regions of homozygosity. The top 1% single-nucleotide polymorphisms (SNPs) were selected and mapped, and the genes were thoroughly investigated. Ten consensus genes were found localized on chromosomes 3-11-14-19, partially confirming previous studies. The HEPACAM2, CDK6, and FAH genes, related to the transforming growth factor β (TGF-β) pathway and heart development, also emerged in the ROH analysis. In conclusion, this work expands the knowledge of the genetic basis of MMVD by identifying genes involved in the early onset of MMVD in CKCSs.

Disease Severity-Associated Gene Expression in Canine Myxomatous Mitral Valve Disease Is Dominated by TGFβ Signaling

Myxomatous mitral valve disease (MMVD) is the most common acquired canine cardiovascular disease and shares many similarities with human mitral valvulopathies. While transcriptomic datasets are available for the end-stage disease in both species, there is no information on how gene expression changes as the disease progresses, such that it cannot be stated with certainty if the changes seen in end-stage disease are casual or consequential. In contrast to humans, the disease in dogs can be more readily examined as it progresses, and this allows an opportunity for insight into disease pathogenesis relevant to both species. The aim of this study was to identify changes in valve gene expression as canine MMVD advances over an entire life-time, from normal (grade 0) to severely affected (grade 4), and differences in gene expression comparing normal and disease areas of the same valve. Transcriptomic profiling identified 1002 differentially expressed genes (DEGs) across all four disease grades when compared with normal valves with the greatest number of DEGs in grade 3 (673) and grade 4 (507). DEGs were associated with a large number of gene families, including genes encoding cytoskeletal filaments, peptidases, extra-cellular matrix (ECM) proteins, chemokines and integrins. Gene enrichment analysis identified significant grade-dependent changes in gene clustering, with clusters trending both up and down as disease progressed. Significant grade-dependent changes in hallmark disease gene expression intensity were identified, including ACTA2, HTR2B, MMP12, and CDKN2A. Gene Ontology terms were dominated by terms for ECM and inflammation with TGFβ1, TNF, IFGN identified as the top up-stream regulators in both whole and dissected diseased valve samples. These data show that while disease progression in MMVD is associated with increasing numbers of DEGs, TGFβ appears to be the dominant signaling pathway controlling pathogenesis irrespective of disease severity.

Genome-wide association study of degenerative mitral valve disease in Maltese dogs

Genome-wide association study (GWAS) is a powerful tool for identifying the genetic causes of various diseases. This study was conducted to identify genomic variation in Maltese dog genomes associated with degenerative mitral valve disease (DMVD) development and to evaluate the association of each biological condition with DMVD in Maltese dogs. DNA was extracted from blood samples obtained from 48 Maltese dogs (32 with DMVD and 16 controls). Genome-wide single nucleotide polymorphism (SNP) genotyping was performed. The top 30 SNPs from each association of various conditions and genetic variations were mapped to their gene locations. A total of 173,662 loci were successfully genotyped, with an overall genotype completion rate of 99.41%. Quality control analysis excluded 46,610 of these SNPs. Manhattan plots were produced using allelic tests with various candidate clinical conditions. A significant peak of association was observed between mitral valve prolapse (MVP) and SNPs on chromosome 17. The present study revealed significant SNPs in several genes associated with cardiac function, including PDZ2, Armadillo repeat protein detected in velo-cardio-facial syndrome, catenin (cadherin-associated protein) alpha 3, low-density lipoprotein receptor class A domain containing protein 4, and sterile alpha motif domain containing protein 3. To our knowledge, this is the first study of a genetic predisposition to DMVD in Maltese dogs. Although only a limited number of cases were analyzed, these data could be the basis for further research on the genetic predisposition to MVP and DMVD in Maltese dogs.

Genetics of syndromic and non-syndromic mitral valve prolapse

Mitral valve prolapse (MVP) is a common condition that affects 2%-3% of the general population. MVP is thought to include syndromic forms such as Marfan syndrome and non-syndromic MVP, which is the most frequent form. Myxomatous degeneration and fibroelastic deficiency (FED) are regarded as two different forms of non-syndromic MVP. While FED is still considered a degenerative disease associated with ageing, frequent familial clustering has been demonstrated for myxomatous MVP. Familial and genetic studies led to the recognition of reduced penetrance and large phenotypic variability, and to the identification of prodromal or atypical forms as a part of the complex spectrum of the disease. Whereas autosomal dominant mode is the common inheritance pattern, an X linked form of non-syndromic MVP was recognised initially, related to Filamin-A gene, encoding for a cytoskeleton protein involved in mechanotransduction. This identification allowed a comprehensive description of a new subtype of MVP with a unique association of leaflet prolapse and paradoxical restricted motion in diastole. In autosomal dominant forms, three loci have been mapped to chromosomes 16p11-p12, 11p15.4 and 13q31-32. Although deciphering the underlying genetic defects is still a work in progress, DCHS1 mutations have been identified (11p15.4) in typical myxomatous disease, highlighting new molecular pathways and pathophysiological mechanisms leading to the development of MVP. Finally, a large international genome-wide association study demonstrated the implication of frequent variants in MVP development and opened new directions for future research. Hence, this review focuses on phenotypic, genetic and pathophysiological aspects of MVP.

Evaluation of genes associated with human myxomatous mitral valve disease in dogs with familial myxomatous mitral valve degeneration

Myxomatous mitral valve disease (MMVD) is the most common heart disease in the dog. It is believed to be heritable in Cavalier King Charles spaniels (CKCS) and Dachshunds. Myxomatous mitral valve disease is a familial disease in human beings as well and genetic mutations have been associated with its development. We hypothesized that a genetic mutation associated with the development of the human form of MMVD was associated with the development of canine MMVD. DNA was isolated from blood samples from 10 CKCS and 10 Dachshunds diagnosed with MMVD, and whole genome sequences from each animal were obtained. Variant calling from whole genome sequencing data was performed using a standardized bioinformatics pipeline for all samples. After filtering, the canine genes orthologous to the human genes known to be associated with MMVD were identified and variants were assessed for likely pathogenic implications. No variant was found in any of the genes evaluated that was present in least eight of 10 affected CKCS or Dachshunds. Although mitral valve disease in the CKCS and Dachshund is a familial disease, we did not identify genetic cause in the genes responsible for the human disease in the dogs studied here.