Proliferative, lymphocytic, infundibular mural folliculitis and dermatitis with prominent follicular apoptosis and parakeratotic casts in a Labrador retriever: Clinical, histopathological and dermoscopic features and co-morbidities

Proliferative, lymphocytic, infundibular mural folliculitis and dermatitis have been reported in six female Labrador retrievers from North America. This is the first report of the disease outside North America, describing the clinical and histopathological diagnosis and dermoscopic aspect of the verrucous plaques, treatment and co-morbidities in a female Labrador retriever dog.

No evidence that long runs of homozygosity tend to harbor risk variants for polygenic obesity in Labrador retriever dogs

Canine polygenic obesity can be influenced by relatively recent mutations with large effects. We determined whether, as with monogenic diseases, long autozygous tracts may be disproportionately likely to harbor detrimental variants for additive polygenic obesity in Labrador retriever dogs. Both our detection of runs of homozygosity (ROH) and our preliminary association study were based on whole-genome sequencing of 28 obese and 22 healthy dogs. We detected and analyzed the distribution of 19,655 ROH. We observed 237 and 98 ROH-harboring genotypes associated with obesity and increased body mass, respectively. We found no evidence that long ROH tend to harbor genotypes linked to obesity or increased body weight, and we concluded that data on ROH overlapping GWAS signals for canine obesity are unlikely to help prioritize candidate genes for validation studies.

Genotype frequency of ATP7A and ATP7B mutation-related copper-associated hepatitis in a Japanese guide dog Labrador retriever population

The incidence of copper-associated hepatitis in Labrador retriever in Japan has not been examined. This study examined the genotype frequencies of ATP7B:c.4358G>A, a mutation responsible for copper-associated hepatitis, and ATP7A:c.980C>T, a modifier of this disease, in Labrador retrievers of guide dog associations in Japan. Genetic material was collected by buccal swabs from 253 Labrador retrievers and genotyping was performed for the ATP7B and ATP7A mutations. The gene frequency was 0.107 for ATP7B:c.4358A. For ATP7A:c.980C, the gene frequencies were 0.703 in females and 0.368 in males. In this study, we established genotyping methods for the ATP7B:c.4358G>A and ATP7A:c.980C>T mutations. Based on the genotyping results, the risk of copper-associated hepatitis in the study population was 0.80% in males and 1.05% in females.

A CNTNAP1 Missense Variant Is Associated with Canine Laryngeal Paralysis and Polyneuropathy

Laryngeal paralysis associated with a generalized polyneuropathy (LPPN) most commonly exists in geriatric dogs from a variety of large and giant breeds. The purpose of this study was to discover the underlying genetic and molecular mechanisms in a younger-onset form of this neurodegenerative disease seen in two closely related giant dog breeds, the Leonberger and Saint Bernard. Neuropathology of an affected dog from each breed showed variable nerve fiber loss and scattered inappropriately thin myelinated fibers. Using across-breed genome-wide association, haplotype analysis, and whole-genome sequencing, we identified a missense variant in the CNTNAP1 gene (c.2810G>A; p.Gly937Glu) in which homozygotes in both studied breeds are affected. CNTNAP1 encodes a contactin-associated protein important for organization of myelinated axons. The herein described likely pathogenic CNTNAP1 variant occurs in unrelated breeds at variable frequencies. Individual homozygous mutant LPPN-affected Labrador retrievers that were on average four years younger than dogs affected by geriatric onset laryngeal paralysis polyneuropathy could be explained by this variant. Pathologic changes in a Labrador retriever nerve biopsy from a homozygous mutant dog were similar to those of the Leonberger and Saint Bernard. The impact of this variant on health in English bulldogs and Irish terriers, two breeds with higher CNTNAP1 variant allele frequencies, remains unclear. Pathogenic variants in CNTNAP1 have previously been reported in human patients with lethal congenital contracture syndrome and hypomyelinating neuropathy, including vocal cord palsy and severe respiratory distress. This is the first report of contactin-associated LPPN in dogs characterized by a deleterious variant that most likely predates modern breed establishment.

Investigation of Genetic Modifiers of Copper Toxicosis in Labrador Retrievers

Copper toxicosis is a complex genetic disorder in Labrador retrievers characterized by hepatic copper accumulation eventually leading to liver cirrhosis. The variation of hepatic copper levels in Labrador retrievers has been partly explained by mutations in ATP7A c.980C>T and ATP7B c.4358G>A. To further elucidate the genetic background of this disease, we used targeted Next Generation Sequencing (NGS) in a cohort of 95 Labrador retrievers to analyze 72 potential modifier genes for variations associated with hepatic copper levels. Variants associated with copper levels were subsequently evaluated in a replication cohort of 144 Labrador retrievers. A total of 44 variants in 25 different genes were identified, of which four showed significant association with copper levels. Of the four variants found associated with hepatic copper levels in the NGS cohort, one was validated in the replication cohort. The non-reference allele of the variant NC_006602.3.g.52434480C>T in RETN resulting in amino-acid change p.Leu7Phe was associated with decreased hepatic copper levels. In humans, resistin is associated with severity of non-alcoholic fatty liver disease, fibrosis, cirrhosis and mitochondrial dysfunction in hepatocytes. Further studies are needed to investigate the biological function of RETN p.Leu7Phe in the development of copper toxicosis in Labrador retrievers.

Variation in breeding practices and geographic isolation drive subpopulation differentiation, contributing to the loss of genetic diversity within dog breed lineages

Background

Discrete breed ideals are not restricted to delimiting dog breeds from another, but also are key drivers of subpopulation differentiation. As genetic differentiation due to population fragmentation results in increased rates of inbreeding and loss of genetic diversity, detecting and alleviating the reasons of population fragmentation can provide effective tools for the maintenance of healthy dog breeds.

Results

Using a genome-wide SNP array, we detected genetic differentiation to subpopulations in six breeds, Belgian Shepherd, English Greyhound, Finnish Lapphund, Italian Greyhound, Labrador Retriever and Shetland Sheepdog, either due to geographical isolation or as a result of differential breeding strategies. The subpopulation differentiation was strongest in show dog lineages.

Conclusions

Besides geographical differentiation caused by founder effect and lack of gene flow, selection on champion looks or restricted pedigrees is a strong driver of population fragmentation. Artificial barriers for gene flow between the different subpopulations should be recognized, their necessity evaluated critically and perhaps abolished in order to maintain genetic diversity within a breed. Subpopulation differentiation might also result in false positive signals in genome-wide association studies of different traits.

Lay summary

Purebred dogs are, by definition, reproductively isolated from other breeds. However, similar isolation can also occur within a breed due to conflicting breeder ideals and geographic distances between the dog populations. We show here that both of these examples can contribute to breed division, with subsequent loss of genetic variation in the resulting breed lineages. Breeders should avoid creating unnecessary boundaries between breed lineages and facilitate the exchange of dogs between countries.

Heritabilities for the puppy weight at birth in Labrador retrievers

Background

Weight at birth is an important predictor of neonatal mortality and morbidity in dogs. In addition, the birthweight of the puppies in a litter influences the decision to perform a cesarean section. The goal of the present study was to estimate heritabilities for the puppy birth weight in Labrador retrievers.

Results

Of the 1138 Labrador retriever litters whelped at the Guiding Eye for the Blind between September 2001 and February 2018, 1013 were included in the analyses after data editing. Puppy weight at birth was the target trait, measured on a continuous scale in pounds, and converted to grams. Linear mixed models were used to identify factors influencing puppy weight at birth. The analyses showed that the sex of the puppy, litter size, length of gestation, adult weight of the dam, parity, year of birth and inbreeding coefficient of the puppies and dams contributed to the variance of the puppy birth weight. Dam and litter effects were included as random effects. A multiple trait derivative free restricted maximum likelihood approach was used to estimate variance components and genetic parameters with two animal models, one without covariates (Model 1) and one with covariates (Model 2). Sex of the puppy and litter size had moderate effects, whereas gestation length, adult weight of the dam, parity, year of birth and inbreeding coefficients of the dam and the puppies had minor effects. Estimates for Model 1 and Model 2 were 0.21 and 0.17 for the direct heritabilities, 0.22 and 0.22 for the maternal additive genetic heritabilities, 0.07 and 0.07 for the maternal permanent environmental proportions, and 0.14 and 0.08 for the environmental proportion of the litter.

Conclusions

In order to estimate reliable breeding values for puppy weight at birth, sex of puppy, litter size, length of gestation and the adult weight of the dam should be included. Estimates could benefit from weighing the dams prior to each mating.

Quantification of the health-status of the Dutch Labrador retriever population

Health issues in purebred dogs are currently considered one of the biggest problems in companion animal health. The Labrador retriever (LR) is one of the most popular dog breeds. The aim of this study was to quantify LR breed health in comparison with mixed-breed dogs (MB), by using four different data sources: a veterinary practice management system (appr. 35,000 unique individuals LR + MB), data from two animal insurance companies (appr. 15,500 and 4500 individuals respectively), and a histopathological laboratory (appr. 4000 individuals). After extensive recoding of the data, health parameters utilised to quantify breed health were longevity, frequency of practice visits and insurance expense claims, and diagnostic codes. A Kaplan-Meier univariate and multivariable Cox proportional hazard model were used to evaluate longevity. A negative binomial model was used to analyse the frequency of visits, claims, and diagnostic codes in both sets of insurance data. Logistic regression was used to look into the categorical diagnostic codes in the laboratory data. The median lifespan of the LR was similar (12 years, practice data) or longer (10 versus 8 years, insurance data) than MB for individuals with a known birth and death date. When including censored individuals, survival time in the LR was comparable to MB individuals up to 10 years of age. Above 10 years of age, the LR lived a similar length as MB with a medium to large body size, but shorter than all MB. The LR visited the veterinary practice more often (risk ratio (RR) 1.2, 95% confidence interval 1.2-1.3), and also showed a higher frequency of insurance expense claims (RR 2.2 (2.1-2.3) and RR 1.2 (1.1-1.3) respectively for the two insurance data sets). The largest difference in organ systems between the LR and MB in insurance claims was related to ears (RR 5.3 (4.8-5.8) and RR 2.6 (2.3-3.1)), followed by airways (RR 2.6 (2.4-2.8)), tendons & muscles (RR 2.4 (2.2-2.6) and RR 1.4 (1.1-1.7)), and joints (RR 1.7 (1.3-2.1)), without a difference in median age at diagnosis. The data from the histopathological laboratory suggested a higher disease burden related to oncology for the LR compared to MB (OR 1.2, 95% CI 1.0-1.3). Oncological diagnoses were made at a younger age in the LR (8.8 versus 9.4 years). The disease burden was significantly higher for the LR than MB, but these results may suffer from substantial bias such as selection bias towards the database, and different behaviour of LR versus MB owners with regards to veterinary care. In the future, longer term population data can corroborate these results.

Factors contributing to the decision to perform a cesarean section in Labrador retrievers

BACKGROUND

In the past 10 years, the frequency of unplanned cesarean sections in the Labrador Retriever breeding colony at Guiding Eyes for the Blind stayed around 10% (range 5% to 28%). To reduce the number of cesarean sections, factors influencing the occurrence of a cesarean section need to be known. The goal of this study was to identify factors that contribute to the decision to perform a cesarean section.

RESULTS

Of the 688 Labrador Retriever litters whelped between 2003 and 2016, 667 litters had sufficient data and remained in the analysis. The target trait was ordinal with the three levels "normal whelping", "assisted whelping" and "cesarean section". A general ordinal logistic regression approach was used to analyze the data. Model selection with possible predictors resulted in a final model including weight of the dam, the weight of the heaviest puppy of a litter, the number of fetuses malpositioned and the quality of uterine contractions. Weight and size of a litter, parity, maternal inbreeding coefficient, whelping season, dam and sire were dropped from the model because they were not significant. The risk of a cesarean section was influenced by the combination of the weight of the dam and the weight of the heaviest puppy in the litter, as well as by the number of malpositioned fetuses and the quality of the contractions. Larger puppies increased the risk of cesarean section especially when the dam had a lighter weight. For dams weighing 23.6 kg and 32.8 kg the predicted probability of a cesarean section was low, with 0.06 and 0.02, respectively, when the heaviest puppy in a litter was light (0.42 kg), contractions were normal and no fetus was malpositioned. However, the probability of a cesarean section was much higher, ranging from 0.24 to 0.08, when the heaviest puppy in a litter was heavy (0.66 kg).

CONCLUSIONS

Means to reduce the cesarean section frequency in this Labrador Retriever breeding colony should include genetic selection for ideal puppy weight. In addition, dams with an adult body weight substantially below average should not be selected as breeders in this colony.

Canine Copper-Associated Hepatitis

Copper-associated hepatitis is recognized with increasing frequency in dogs. The disease is characterized by centrolobular hepatic copper accumulation, leading to hepatitis and eventually cirrhosis. The only way to establish the diagnosis is by histologic assessment of copper distribution and copper quantification in a liver biopsy. Treatment with the copper chelator d-penicillamine is the most commonly used treatment. In addition, a low-copper/high-zinc diet can help prevent accumulation or reaccumulation of hepatic copper. Mutations in the copper metabolism genes COMMD1 or ATP7A and ATP7B have been associated with hepatic copper concentrations in Bedlington terriers and Labrador retrievers respectively. In the Labrador retriever, dietary copper intake contributes strongly to the disease phenotype.

Similar recent selection criteria associated with different behavioural effects in two dog breeds

Selection during the last decades has split some established dog breeds into morphologically and behaviourally divergent types. These breed splits are interesting models for behaviour genetics since selection has often been for few and well-defined behavioural traits. The aim of this study was to explore behavioural differences between selection lines in golden and Labrador retriever, in both of which a split between a common type (pet and conformation) and a field type (hunting) has occurred. We hypothesized that the behavioural profiles of the types would be similar in both breeds. Pedigree data and results from a standardized behavioural test from 902 goldens (698 common and 204 field) and 1672 Labradors (1023 and 649) were analysed. Principal component analysis revealed six behavioural components: curiosity, play interest, chase proneness, social curiosity, social greeting and threat display. Breed and type affected all components, but interestingly there was an interaction between breed and type for most components. For example, in Labradors the common type had higher curiosity than the field type (F_1,1668 = 18.359; P < 0.001), while the opposite was found in goldens (F_1,897 = 65.201; P < 0.001). Heritability estimates showed considerable genetic contributions to the behavioural variations in both breeds, but different heritabilities between the types within breeds was also found, suggesting different selection pressures. In conclusion, in spite of similar genetic origin and similar recent selection criteria, types behave differently in the breeds. This suggests that the genetic architecture related to behaviour differs between the breeds.

Protein expression and genetic variability of canine Can f 1 in golden and Labrador retriever service dogs

BACKGROUND

Valued for trainability in diverse tasks, dogs are the primary service animal used to assist individuals with disabilities. Despite their utility, many people in need of service dogs are sensitive to the primary dog allergen, Can f 1, encoded by the Lipocalin 1 gene (LCN1). Several organizations specifically breed service dogs to meet special needs and would like to reduce allergenic potential if possible. In this study, we evaluated the expression of Can f 1 protein and the inherent variability of LCN1 in two breeds used extensively as service dogs. Saliva samples from equal numbers of male and female Labrador retrievers (n = 12), golden retrievers (n = 12), and Labrador-golden crosses (n = 12) were collected 1 h after the morning meal. Can f 1 protein concentrations in the saliva were measured by ELISA, and the LCN1 5' and 3' UTRs and exons sequenced.

RESULTS

There was no sex effect (p > 0.2) nor time-of-day effect; however, Can f 1 protein levels varied by breed with Labrador retrievers being lower than golden retrievers (3.18 ± 0.51 and 5.35 ± 0.52 μg/ml, respectively, p < 0.0075), and the Labrador-golden crosses having intermediate levels (3.77 ± 0.48 μg/ml). Although several novel SNPs were identified in LCN1, there were no significant breed-specific sequence differences in the gene and no association of LCN1 genotypes with Can f 1 expression.

CONCLUSIONS

As service dogs, Labrador retrievers likely have lower allergenic potential and, though there were no DNA sequence differences identified, classical genetic selection on the estimated breeding values associated with salivary Can f 1 expression may further reduce that potential.

Noninvasive Assessment of Neuromuscular Disease in Dogs: Use of the 6-minute Walk Test to Assess Submaximal Exercise Tolerance in Dogs with Centronuclear Myopathy

Background

Noninvasive methods of quantitating exercise tolerance in dogs with neuromuscular disease are needed both for clinical and research use. The 6‐minute walk test (6MWT) has been validated as a reliable test of exercise tolerance in dogs with pulmonary and cardiac disease, but not in dogs with neuromuscular disease.

Hypothesis/Objectives

Distance walked and number of steps taken during 6MWT will differ between Labrador retriever dogs with centronuclear myopathy (CNM) and control (ie, healthy) littermates.

Animals

Eight purebred Labrador retrievers were drawn from a purpose‐bred research colony (status: 3 clear, 2 carrier, and 3 homozygous mutants for the protein tyrosine phosphatase‐like A (PTPLA) gene mutation associated with CNM).

Methods

Pilot, prospective, Case–controlled study. Researchers were blinded to disease status. Each dog was leash‐trained and acclimatized to the testing area (length, 12.8 m). At the start of testing, each animal was fitted with a pedometer, a timer was started, and dogs were allowed to walk at their own pace for 6 minutes. Distance walked and pedometer readings were recorded.

Results

Degree of paresis varied among affected dogs, and was reflected by significant differences in distance walked between CNM‐affected dogs and those with clear and carrier genotypes (P = .048). Pedometer readings did not vary according to genotype (P = .86).

Conclusions

The 6MWT appears to differentiate between the ambulatory capacity of normal and CNM‐affected dogs. Additional studies are needed to confirm this relationship in a larger number of dogs, and to evaluate the ability of the 6MWT to differentiate between dogs with variable severity of neuromuscular disease‐associated exercise intolerance.

Canine Models for Copper Homeostasis Disorders

Copper is an essential trace nutrient metal involved in a multitude of cellular processes. Hereditary defects in copper metabolism result in disorders with a severe clinical course such as Wilson disease and Menkes disease. In Wilson disease, copper accumulation leads to liver cirrhosis and neurological impairments. A lack in genotype-phenotype correlation in Wilson disease points toward the influence of environmental factors or modifying genes. In a number of Non-Wilsonian forms of copper metabolism, the underlying genetic defects remain elusive. Several pure bred dog populations are affected with copper-associated hepatitis showing similarities to human copper metabolism disorders. Gene-mapping studies in these populations offer the opportunity to discover new genes involved in copper metabolism. Furthermore, due to the relatively large body size and long life-span of dogs they are excellent models for development of new treatment strategies. One example is the recent use of canine organoids for disease modeling and gene therapy of copper storage disease. This review addresses the opportunities offered by canine genetics for discovery of genes involved in copper metabolism disorders. Further, possibilities for the use of dogs in development of new treatment modalities for copper storage disorders, including gene repair in patient-derived hepatic organoids, are highlighted.

Normal clinical electroretinography parameters for poodle, Labrador retriever, Thai ridgeback, and Thai Bangkaew

The purpose of the present study was to establish normal electroretinogram (ERG) parameters using 56 normal eyes of four dog breeds common in Thailand: poodle, Labrador retriever, Thai ridgeback, and Thai Bangkaew. Standard ERG findings were bilaterally recorded using a handheld multi-species ERG unit with an ERG-jet lens electrode for 28 dogs under preanesthesia with diazepam, anesthesia with propofol, and anesthesia maintenance with isoflurane. There were significant differences in the mean values of ERG amplitudes and implicit times among the four dog breeds (p < 0.05) except for the b-wave implicit time of the photopic 30 Hz flicker response with 3 cd.s/m(2) (p = 0.610). Out of the four breeds, Thai Bangkaew had the longest implicit time (p < 0.001) of scotopic low intensity responses, b-wave of scotopic standard intensity responses (3 cd.s/m(2)), a-wave of the higher intensity response (10 cd.s/m(2)), and a-wave of the photopic single flash response (3 cd.s/m(2)). For the b/a ratio, only the ratio of the Cone response was significantly different among the different breeds. In this summary, normal ERG parameters for four dog breeds were reported. Data from the investigation supported the hypothesis that determination of breed-specific limits of normality for ERG responses is necessary for individual clinics and laboratories.

Successful management permitting delayed operative revision of cleft palate in a labrador retriever

Congenital palate defects (CP) occur in dogs. Secondary cleft palate (SCP) is a congenital oronasal fistula resulting in incomplete closure of the hard and soft palate. SCP occurs alone or in combination with primary cleft palate involving the lip and premaxilla. CP results from incomplete fusion of the palatine shelves, most critical at 25 to 28 days gestation. Methods to improve survival of puppies with CP are sought by clients. This case report illustrates a successful method to manage nutrition in affected dogs until adult size is attained, facilitating surgical correction.

Peripheral neuroblastomas in dogs: a case series

The peripheral neuroblastic tumours (PNTs) include neuroblastoma, ganglioneuroblastoma and ganglioneuromas. These subtypes reflect a spectrum of differentiation of progenitor cells of the sympathetic nervous system from tumours with predominant undifferentiated neuroblasts to those consisting of neuronal cell bodies that are well differentiated. Peripheral neuroblastoma is a tumour composed of neuroblastic cells with no or limited neuronal differentiation. In dogs, peripheral neuroblastoma is rare. The present report documents nine cases of canine peripheral neuroblastoma, the majority occurring as large masses in the craniodorsal abdominal cavity of young dogs (mean age of 3 years at diagnosis). Microscopically, all of the masses consisted of round to oval cells with a scant cytoplasm and hyperchromatic nuclei. Homer-Wright rosettes and pseudorosettes were evident in three of the nine cases. Neoplastic cells were immunoreactive in varying degrees to S100, neuron-specific enolase, synaptophysin, chromogranin A, tyrosine hydroxylase (one case) and were negative for vimentin, cytokeratin, CD3 and CD79a, indicating a neurogenic nature. Four of the nine cases occurred in Labrador retrievers (44%) and two (22%) in boxers, suggesting a possible breed predisposition.