The occurrence and suspected mode of inheritance of congenital subaortic stenosis and tricuspid valve dysplasia in Dogue de Bordeaux dogs

Molecular Pathways and Animal Models of Ebstein's Anomaly

Ebstein's anomaly is a congenital malformation of the tricuspid valve characterized by abnormal attachment of the valve leaflets, resulting in varying degrees of valve dysfunction. The anatomic hallmarks of this entity are the downward displacement of the attachment of the septal and posterior leaflets of the tricuspid valve. Additional intracardiac malformations are common. From an embryological point of view, the cavity of the future right atrium does not have a direct orifice connected to the developing right ventricle. This chapter provides an overview of current insight into how this connection is formed and how malformations of the tricuspid valve arise from dysregulation of molecular and morphological events involved in this process. Furthermore, mouse models that show features of Ebstein's anomaly and the naturally occurring model of canine tricuspid valve malformation are described and compared to the human model. Although Ebstein's anomaly remains one of the least understood cardiac malformations to date, the studies summarized here provide, in aggregate, evidence for monogenic and oligogenic factors driving pathogenesis.

Cardiac Disease and Screening in Breeding Dogs

Acquired and congenital heart diseases are relatively common in dogs, particularly in certain breeds. Modes of inheritance and genetic causes have been established for several cardiac diseases within various breeds. Breed screening is used to try and reduce the prevalence of certain canine cardiac diseases. Although breed screening seems to help reduce the prevalence of canine heart disease, the outcomes of specific breeding programs are variable and depend on multiple factors.

Natural history of subaortic stenosis in 166 dogs (1999-2011)

INTRODUCTION

Subaortic stenosis (SAS) is one of the most common congenital cardiac diseases in dogs. The objective of this study was to provide survival times on a large population of dogs with SAS and to propose a redefined pressure gradient (PG) scale to include a mild, moderate, severe and very severe disease group.

ANIMALS, MATERIALS AND METHODS

Dogs were divided into four groups based on the Doppler-derived PG across the stenosis. Disease severity was defined as follows: mild = PG < 50 mmHg; moderate = PG range 50-80 mmHg; severe = PG range 80-130 mmHg; and very severe = PG > 130 mmHg. Over the study period (1999-2011), 166 client-owned dogs were diagnosed with SAS of which 129 had follow-up information available.

RESULTS

Unadjusted median survival time for severity groups were as follows: mild 10.6 years; moderate 9.9 years; severe 7.3 years; and very severe 3.0 years. Univariable analysis examining the effect of the PG, age at diagnosis and sex found only the PG and age at diagnosis had a significant effect on survival. Adjusted survival curves showed that the survival time in the very severe group was decreased compared with all other groups.

CONCLUSION

Based on the results of this study, a revised SAS classification system with four PG groups is appropriate. Dogs with a PG > 130 mmHg were identified as those with the lowest median survival time.

Identification and Clinical Significance of Heart Murmurs in Puppies Involved in Puppy Trade

The detection of a congenital heart defect at purchase is an important step in early detection from a clinical and legal standpoint. Indeed, some cardiac abnormalities may be corrected with surgery, and very often, treatment needs to be performed early before congestive heart failure or irreversible heart damage can occur. From a legal viewpoint, if the defect is revealed in a newly purchased puppy, the buyer may be required to return it and receive compensation. Puppies affected with congenital heart defects are likely to die prematurely, causing emotional suffering to the owner. Furthermore, by considering breed predisposition, early recognition allows breeders to avoid breeding from particular dogs with genetic defects and prevent the continuation of genetic defects in breeding lines. Given gaps in the literature about the recognition of murmurs in the puppy trade, the present article describes how to identify a heart murmur in a puppy during a pre-purchase examination and its significance from a clinical and legal viewpoint. In the canine population, the prevalence of cardiac defects ranges between 0.13 and 1.6%. Pulmonic stenosis is the most common defect found in puppies, followed by patent ductus arteriosus, subaortic stenosis, and ventricular septal defect. On the basis of the above considerations, the veterinarian should recognize and identify the murmur following a protocol for routine examination of puppies involved in trade.

Genetics of canine subvalvular aortic stenosis (SAS)

Subvalvular aortic stenosis (SAS) is one of the most common congenital heart defects of dogs. The disease is characterized by obstruction of the left ventricular outflow tract, resulting in pressure overload on the left ventricle. The etiology of obstruction is a fibromuscular nodule, ridge, or ring of tissue that increases aortic outflow tract velocity. This review is focused on the prevalence, inheritance pattern, and current genetic insights of canine SAS. The prevalence of this disease was reported at 4.7 % in a large veterinary referral hospital. The mode of inheritance for this disease has also been described in breeds with a high disease prevalence such as the Bullmastiff, Bouvier des Flandres, Dogue de Bordeaux, Golden Retriever, Newfoundland, and Rottweiler. Genetic investigations seeking to identify causative mutations for SAS are lacking with only a single published variant associated with SAS in Newfoundlands.

Epidemiological study of congenital heart diseases in dogs: Prevalence, popularity, and volatility throughout twenty years of clinical practice

The epidemiology of Congenital Heart Diseases (CHDs) has changed over the past twenty years. This study aimed to evaluate the prevalence of CHDs in the population of dogs recruited in a single referral center (RC); compare the epidemiological features of CHDs in screened breeds (Boxers) versus non-screened (French and English Bulldogs, German Shepherds); investigate the association of breeds with the prevalence of CHDs; determine the popularity and volatility of breeds over a 20-year period; analysed the trends of the most popular breeds in the overall population of new-born dogs registered in the Italian Kennel Club (IKC) from 1st January 1997 to 31st December 2017. The RC's cardiological database was analysed, and 1,779 clinical records were included in a retrospective observation study. Descriptive statistics and frequencies regarding the most representative breeds and CHDs were generated. A logistic regression model was used to analyse the trends of the most common CHDs found in single and in cluster of breeds. The relationship between breed popularity and presence of CHDs was studied. The most common CHDs were Pulmonic Stenosis, Patent Ductus Arteriosus, Subaortic Stenosis, Ventricular Septal Defect, Aortic Stenosis, Tricuspid Dysplasia, Atrial Septal Defect, Double Chamber Right Ventricle, Mitral Dysplasia, and others less frequent. The most represented pure breeds were Boxer, German Shepherd, French Bulldog, English Bulldog, Maltese, Newfoundland, Rottweiler, Golden Retriever, Chihuahua, and others in lower percentage. Chihuahuas, American Staffordshire Terriers, Border Collies, French Bulldogs, and Cavalier King Charles Spaniel were the most appreciated all of which showed a high value of volatility. This study found evidence for the value of the screening program implemented in Boxers; fashions and trends influence dog owners' choices more than the worries of health problems in a breed. Effective breeding programs are needed in order to control the diffusion of CHDs without impoverishing the genetic pool.

Membranous subaortic stenosis coexisting with hypertrophic cardiomyopathy: A case report

Subaortic stenosis (SAS) is a congenital heart disease, and its association with hypertrophic cardiomyopathy is very rare and clinically underappreciated. We report here a case of a 45-year-old female who was admitted to our hospital with chest tightness and shortness of breath. Both transthoracic and transesophageal echocardiography revealed asymmetric left ventricular hypertrophy and a membrane-like echo below the level of the aortic valve. This patient was diagnosed with membranous SAS with hypertrophic cardiomyopathy. Screening of her immediate family members revealed that her son also had hypertrophic cardiomyopathy. The patient chose conservative treatments and has been closely followed-up after discharge.

Phenotypic description of cardiac findings in a population of Dogue de Bordeaux with an emphasis on atrial fibrillation

The aim of this study was to describe the clinical phenotype of Dogue de Bordeaux (DdB) referred for cardiac investigation, with particular reference to the prevalence of atrial fibrillation and associated features. Review of canine medical records of two United Kingdom veterinary referral hospitals identified 64 DdB with available echocardiographic and electrocardiographic (ECG)/Holter data. Atrial fibrillation was documented in 25 (39%) dogs and supraventricular tachycardia was recorded in five (7.8%) dogs. In a subset of 34 dogs, excluding congenital heart disease (n=17), presence of a cardiac mass (n=7) and non-cardiac neoplasia (n=6), 19 (56%) dogs had atrial fibrillation, with a median heart rate of 200 beats per min (bpm) on presentation. Atrial fibrillation was inconsistently associated with cardiac chamber remodelling, but was frequently associated with systolic dysfunction (13/19, 68.4%) and right sided atrial or ventricular dilatation (14/19, 73.7%) in dogs with atrial fibrillation in this subset. No dogs in this subset had right sided atrial or ventricular dilatation in the absence of supraventricular arrhythmia or systolic dysfunction. The absence of structural heart disease in some dogs with supraventricular arrhythmias suggests that an underlying primary arrhythmic process might be responsible for initiating remodelling, although a primary cardiomyopathy cannot be ruled out.

An online health survey of Dogue de Bordeaux owners and breeders with special emphasis on cardiac disease

A questionnaire-based study was undertaken to assess health problems affecting the Dogue de Bordeaux breed of dog and, in particular, the potential impact of cardiac disease. An online survey tool was used to design a questionnaire for Dogue de Bordeaux owners and breeders. After 1year of response time, information was collected on 278 dogs owned by 215 individuals, mostly based in the United Kingdom. Of the 278 dogs, veterinary attention had been sought for chronic skin disease in 63 (22.7%), lameness in 43 (15.5%), gastrointestinal signs in 37 (13.3%) and neoplasia in 28 (10.1%). Cardiac disease was reported in 13/278 dogs (4.7%). At the time of completion of the survey, 55 (19.8%) dogs were dead, 17 (31%) of which were reported to have died suddenly and unexpectedly. Respondents expressed interest in a formal cardiac health screening scheme in the Dogue de Bordeaux breed, but would be reluctant to volunteer for such a scheme if information on disease detected during screening was open access. The incidence of sudden unexpected death was high; although there was no corroboration that the sudden deaths were related to cardiac disease, a possible connection should be explored further.

Tricuspid valve dysplasia: A retrospective study of clinical features and outcome in dogs in the UK

The objective of this study was to determine the demographic, clinical and survival characteristics and to identify risk factors for mortality due to tricuspid valve dysplasia in UK dogs. Records of client-owned dogs diagnosed with tricuspid valve dysplasia at a referral centre were retrospectively reviewed. Only dogs diagnosed with tricuspid valve dysplasia based on the presence of a right-sided heart murmur identified prior to one year of age, and confirmed with Doppler echocardiography, were included. Dogs with concomitant cardiac diseases, pulmonary hypertension and/or trivial tricuspid regurgitation were excluded. Analysed data included signalment, reason for presentation, clinical signs, electrocardiographic and echocardiographic features, survival status and cause of death. Survival times and risk factors for mortality were evaluated using Kaplan-Meier curves and Cox regression. Eighteen dogs met inclusion criteria. Border collies were over-represented (p= 0.014). Dogs were most frequently referred for investigation of heart murmur. The most common arrhythmia was atrial fibrillation (n=3). Median survival time from diagnosis of tricuspid valve dysplasia was 2775 days (range 1-3696 days; 95% CI 1542.41-4007.59) and from onset of right-sided congestive heart failure was 181 days (range 1-2130 days; 95% CI 0-455.59). Syncope was the sole risk factor for cardiac death. In this population of UK dogs, tricuspid valve dysplasia was uncommon but, when severe, frequently led to right-sided congestive heart failure. Prognosis was favourable for mild and moderate tricuspid dysplasia. Survival time was reduced with right-sided congestive heart failure but varied widely. Risk of cardiac death was significantly increased if syncope had occurred.

Combined double chambered right ventricle, tricuspid valve dysplasia, ventricular septal defect, and subaortic stenosis in a dog

BACKGROUND

Double chambered right ventricle (DCRV) is a congenital heart anomaly where the right ventricle is divided into two chambers. We describe, for the first time, an unusual combination of DCRV combined with some other congenital heart defects.

CASE PRESENTATION

A 1.2-year-old Golden Retriever was presented with lethargy, exercise intolerance and ascites. Physical examination revealed an irregularly irregular pulse and a grade V/VI, systolic, right cranial murmur. Electrocardiography revealed widened and splintered QRS complexes with a right bundle-branch block pattern. Radiography demonstrated right-sided cardiomegaly. Two-dimensional echocardiography identified a DCRV with tricuspid valve dysplasia. The patient died despite abdominocentesis and 4 days of oral pharmacotherapy, and necropsy revealed an anomalous fibromuscular structure that divided the right ventricle into two compartments. Another finding was tricuspid valve dysplasia with hypoplasia of the posterior and septal leaflets. The anterior leaflet was prominent, being part of the anomalous structure that divided the right ventricle. Necropsy also identified a perimembranous ventricular septal defect and mild subaortic stenosis. Histopathological examination of the fibromuscular band that separated the right ventricle identified longitudinally oriented layers of dense fibrous connective tissue and myocardial cells arranged in a plexiform pattern. The muscular component was well represented at the ventral area of the fibromuscular band, and was absent in the central zone. Superficially, the endocardium presented areas of nodular hyperplasia covering mainly the fibrous part of the abnormal structure. The nodules were sharply demarcated and were composed by loosely arranged connective tissue with myxoid appearance, covered by discrete hyperplastic endocardium.

CONCLUSIONS

Concomitant cardiac malformations involving DCRV, tricuspid valve dysplasia, perimembranous ventricular septal defect and mild subaortic stenosis have not been previously described in veterinary medicine, and are reported here for the first time. Moreover, this is the first report of a canine patient with tricuspid valve dysplasia (TVD) and DCRV where the anterior leaflet is part of an anomalous structure dividing the right ventricle (RV) into two separate compartments.

Ten inherited disorders in purebred dogs by functional breed groupings

Background

Analysis of 88,635 dogs seen at the University of California, Davis Veterinary Medical Teaching Hospital from 1995 to 2010 identified ten inherited conditions having greater prevalence within the purebred dog population as compared to the mixed-breed dog population: aortic stenosis, atopy/allergic dermatitis, gastric dilatation volvulus (GDV), early onset cataracts, dilated cardiomyopathy, elbow dysplasia, epilepsy, hypothyroidism, intervertebral disk disease (IVDD), and hepatic portosystemic shunt. The objective of the present study was to ascertain if disorders with higher prevalence in purebreds were restricted to particular breed group classifications within the purebred population, specifically the American Kennel Club breed grouping or groups with genomic similarities based upon allele sharing. For each disorder, healthy controls seen at the hospital during that same time period were matched for age, weight, and sex to each affected dog to determine risk of disease presentation in the purebred group as compared to that of the mixed-breed population. To enhance reliability of the analyses, sampling of matched healthy to affected dogs was repeated 50 times. For each comparison, the purebred subgroups to mixed-breed odds ratio was determined as was the mean P value used to test this ratio.

Results

For aortic stenosis, GDV, early onset cataracts, dilated cardiomyopathy, elbow dysplasia, epilepsy, and portosystemic shunt, most purebred groups were not statistically distinct from the mixed-breed population with higher prevalence in purebreds restricted to distinct subsets of purebred dogs. The conditions of atopy/allergic dermatitis, hypothyroidism, and IVDD were more pervasive across the purebred population with many groups having higher prevalence than the mixed-breed population. The prevalence of IVDD in purebred terrier groups was statistically lower than that observed for mixed-breed dogs.

Conclusions

The results offer an assessment of the distribution of inherited disorders within purebred dogs and illustrate how mixed-breed and subpopulations of purebred dogs do not differ statistically in prevalence for certain disorders. Some disorders appear linked to common ancestors providing insight into disease allele origin whereas others may be due to selection for common structural morphology. Knowledge of the origin of a condition may aid in reducing its prevalence in the dog population as a whole.

Electronic supplementary material

The online version of this article (doi:10.1186/s40575-015-0021-x) contains supplementary material, which is available to authorized users.

Insights into morphology and disease from the dog genome project

Although most modern dog breeds are less than 200 years old, the symbiosis between man and dog is ancient. Since prehistoric times, repeated selection events have transformed the wolf into man's guardians, laborers, athletes, and companions. The rapid transformation from pack predator to loyal companion is a feat that is arguably unique among domesticated animals. How this transformation came to pass remained a biological mystery until recently: Within the past decade, the deployment of genomic approaches to study population structure, detect signatures of selection, and identify genetic variants that underlie canine phenotypes is ushering into focus novel biological mechanisms that make dogs remarkable. Ironically, the very practices responsible for breed formation also spurned morbidity; today, many diseases are correlated with breed identity. In this review, we discuss man's best friend in the context of a genetic model to understand paradigms of heritable phenotypes, both desirable and disadvantageous.