SLC3A1 and SLC7A9 mutations in autosomal recessive or dominant canine cystinuria: a new classification system

A retrospective study on epidemiology and management of canine cystine uroliths in one part of Norway from 2015 to 2020

BACKGROUND

Urinary tract problems are a common complaint in small animal medicine and urolithiasis is considered to be an important cause of urinary tract disease in dogs. In this study the main aim was to investigate whether the occurrence of cystine urolithiasis increased during a five-year period. A second aim was to evaluate possible risk-factors as breed, age and gender. This study also evaluated how urine specific gravity, pH and level of cystine in urine responded to preventive strategies. Medical records of dogs with urolithiasis presented at nine Norwegian animal clinics and one animal hospital between 2015 and 2020 were retrospectively reviewed.

RESULTS

The incidence of cystine uroliths increased significantly during the five study years (R2 = 0.72, P = 0.0199). Dogs with cystine uroliths were significantly younger (5.0 years (n = 84, 95% CI [4.4-5.6])) when they were diagnosed with cystine uroliths compared to dogs with other types of uroliths (8.1 years (n = 255, 95% CI[7.8-8.5]) P < < 0.0001). Cystine levels in urine were increased in 93% of the dogs with cystine urolithiasis. Cystinuria decreased significantly after neutering (P < 0.0001). Breeds most commonly affected with cystine urolithiasis in this study were Staffordshire bull terrier, Danish Swedish farmdog and Chihuahua.

CONCLUSIONS

The results from this study supports a suggested genetic basis for cystine urolithiasis as described in previous studies. Neutering is considered an important part of preventing reoccurrence since cystine values decreased significantly after neutering.

[Urinalysis in dogs and cats, part 2: Urine sediment analysis]

Examination of the urine sediment is part of a routine urinalysis and is undertaken in order to identify insoluble particles in the urine. This procedure is mainly used in the context of diagnostic evaluation of urinary tract diseases, but may also be useful for the diagnosis of systemic diseases and intoxications. Analysis of fresh urine is recommended as changes in cell morphology, cell lysis and in vitro crystal formation may occur in the course of its storage. Manual urine sediment analysis is still performed in many veterinary practices. Native wet-mount preparations are suitable for the identification and quantification of urine sediment particles. The examination of stained wet-mount preparations or air-dried smears may be necessary to further differentiate cells and to identify bacteria. For several years, automatic urine sediment analyzers have been available in veterinary medicine. These save considerable time and staff resources, however verification of the automatically generated results by an experienced observer remains necessary. Urine sediment particles that are frequently identified and clinically relevant include red blood cells, white blood cells, different types of epithelial cells, crystals, and casts as well as bacteria. Furthermore, parasite eggs, fungal hyphae, lipid droplets, spermatozoa, fibres, hair, mucus, plant parts or environmental contaminations may be found in the urine sediment and result in a complication of the result interpretation.

Genetic prevalence and clinical relevance of canine Mendelian disease variants in over one million dogs

Hundreds of genetic variants implicated in Mendelian disease have been characterized in dogs and commercial screening is being offered for most of them worldwide. There is typically limited information available regarding the broader population frequency of variants and uncertainty regarding their functional and clinical impact in ancestry backgrounds beyond the discovery breed. Genetic panel screening of disease-associated variants, commercially offered directly to the consumer or via a veterinary clinician, provides an opportunity to establish large-scale cohorts with phenotype data available to address open questions related to variant prevalence and relevance. We screened the largest canine cohort examined in a single study to date (1,054,293 representative dogs from our existing cohort of 3.5 million; a total of 811,628 mixed breed dogs and 242,665 purebreds from more than 150 countries) to examine the prevalence and distribution of a total of 250 genetic disease-associated variants in the general population. Electronic medical records from veterinary clinics were available for 43.5% of the genotyped dogs, enabling the clinical impact of variants to be investigated. We provide detailed frequencies for all tested variants across breeds and find that 57% of dogs carry at least one copy of a studied Mendelian disease-associated variant. Focusing on a subset of variants, we provide evidence of full penetrance for 10 variants, and plausible evidence for clinical significance of 22 variants, on diverse breed backgrounds. Specifically, we report that inherited hypocatalasia is a notable oral health condition, confirm that factor VII deficiency presents as subclinical bleeding propensity and verify two genetic causes of reduced leg length. We further assess genome-wide heterozygosity levels in over 100 breeds, and show that a reduction in genome-wide heterozygosity is associated with an increased Mendelian disease variant load. The accumulated knowledge represents a resource to guide discussions on genetic test relevance by breed.

Lipidomics characterization of the lipid metabolism profiles in a cystinuria rat model: Precalculus damage in the kidney of cystinuria

Cystinuria is a genetic disorder of cystine transport, including defective protein b^0,+AT (encoded by SLC7A9), and/or rBAT (encoded by SLC3A1). Patients present hyperexcretion of cystine in the urine, recurrent cystine lithiasis, and progressive decline in kidney function. Moreover, heterodimer transport is defective. To date, little omics data are accessible regarding this metabolic disease caused by membrane proteins. Since membrane function is closely related to changes in the lipidome, we decided to explore the changes in kidney tissue of a self-established cystinuria rat model by performing lipidomic analysis by LC-MS/MS. Our results demonstrated that Slc7a9 deficiency changed the lipid profile of the renal cortex and induced vital modifications in the lipidome, including major alterations in ChE, LPA, and PA. Among those alterations, this lipidomic study highlights the lipid changes that participate in inflammatory responses during cystinuria. As a result, lipid research, perhaps has great potential, for it may lead to the identification of novel therapeutic targets for the prevention and treatment of cystinuria.

Differences in renal cortex transcriptional profiling of wild-type and novel type B cystinuria model rats

Cystinuria is a genetic disorder of cystine transport that accounts for 1–2% of all cases of renal lithiasis. It is characterized by hyperexcretion of cystine in urine and recurrent cystine lithiasis. Defective transport of cystine into epithelial cells of renal tubules occurs because of mutations of the transport heterodimer, including protein b^0,+AT (encoded by SLC7A9) and rBAT (encoded by SLC3A1) linked through a covalent disulfide bond. Study generated a novel type B cystinuria rat model by artificially deleting 7 bp of Slc7a9 gene exon 3 using the CRISPR-Cas9 system, and those Slc7a9-deficient rats were proved to be similar with cystinuria in terms of genome, transcriptome, translation, and biologic phenotypes with no off-target editing. Subsequent comparisons of renal histopathology indicated model rats gained typical secondary changes as medullary fibrosis with no stone formation. A total of 689 DEGs (383 upregulated and 306 downregulated) were differentially expressed in the renal cortex of cystinuria rats. In accordance with the functional annotation of DEGs, the potential role of glutathione metabolism processes in the kidney of cystinuria rat model was proposed, and KEGG analysis results showed that knock-out of Slc7a9 gene triggered more biological changes which has not been studied. In short, for the first time, a rat model and its transcriptional database that mimics the pathogenesis and clinical consequences of human type B cystinuria were generated.

Variation in mineral types of uroliths from ferrets (Mustela putorius furo) submitted for analysis in North America, Europe, or Asia over an 8-year period

OBJECTIVE

To compare mineral types of naturally occurring uroliths in ferrets (Mustela putorius furo) from North America, Europe, and Asia and to identify potential risk factors associated with cystine urolithiasis in ferrets.

SAMPLES

1,054 laboratory submission records of uroliths obtained from ferrets between January 1, 2010, and December 31, 2018.

PROCEDURES

For this cross-sectional study, the medical records databases at 4 diagnostic laboratories were searched for records of submissions of uroliths obtained from ferrets. Data collection included submission date; ferret sex, neuter status, and age; receiving laboratory and continent; and urolith mineral type. Regression analyses were performed to identify variables associated with cystine uroliths.

RESULTS

Of the 1,054 urolith submissions, 1,013 were from North America, with 92.6% (938/1,013; 95% CI, 90.8% to 94.1%) cystine uroliths, and 41 were from Europe and Asia, with only 26.8% (11/41; 95% CI, 15.7% to 41.9%) cystine uroliths. Median age was 2.0 years for ferrets with cystine urolithiasis versus 4.0 years for those with other types of uroliths. Submissions were more likely cystine uroliths for ferrets in North America versus Europe and Asia (adjusted OR [aOR], 59.5; 95% CI, 21.4 to 165.6), for ferrets that were younger (aOR, 0.67; 95% CI, 0.58 to 0.77), or for submissions in 2018 versus 2010 (aOR, 21.1; 95% CI, 5.1 to 87.9).

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that the proportion of submissions that were cystine uroliths dramatically increased in North America between 2010 and 2018. There is an urgent need to determine underlying causes and mitigate cystine urolithiasis in ferrets.

Mastiff breed mortality: A study of owner experience, dog age and longevity

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Mastiffs are a group of large and giant powerful dogs consisting of 19 breeds worldwide.

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The median age of death for the Mastiff group was 8 years with European and North American dogs also dying at this age.

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A higher percentage of dogs died over 8 years when classed as senior within breed standards.

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Cancer was the most common cause of death in the Mastiff group with osteosarcoma the most common specifically in neutered animals.

Despite being ranked 33 in Americas most popular breeds (American Kennel Club, 2020), there is a lack of research addressing longevity and death related health problems of Mastiff dog breeds and specifically commonly kept Bull Mastiffs and English Mastiffs. Likely a result of small founder populations and minimal breeding geographical locations, limited genetic variation is found making it important to determine key health concerns which may reduce longevity. The purpose of this study was to report findings from an online global survey of owners of deceased Mastiffs detailing breed, age at death, and if known, cause of death. Owner information was also collected including location by continent and country and the owners breeding or hobbyist experience. A closed-question survey was used via an online network of global Mastiff clubs and associations totalling a useable sample of 1036 dogs across a range of breeds. Notably, it is reported that age and cause of death varied dependant on breed. Results indicate that the median age of death for all dogs was 8 years with mean age of death in Europe as 7.72 years and 8.17 years in North America. The most common cause of death identified for all dogs was cancer (47%), old age (16%), cardiac problems (8%) and gastric problems including GDV and bloat (7%). The mean age of death for cancer dogs was 7.85 years with 23 types of cancer stated with Osteosarcoma being the most commonly recorded and specifically for neutered animals. As the survey was aimed at hobbyist and registered breeders, study findings contribute to knowledge of Mastiff mortality with the aim of promoting welfare of the breed.

Cystinuria in Dogs and Cats: What Do We Know after Almost 200 Years?

The purpose of this review is to summarize current knowledge on canine and feline cystinuria from available scientific reports. Cystinuria is an inherited metabolic defect characterized by abnormal intestinal and renal amino acid transport in which cystine and the dibasic amino acids ornithine, lysine, and arginine are involved (COLA). At a normal urine pH, ornithine, lysine, and arginine are soluble, but cysteine forms a dimer, cystine, which is relatively insoluble, resulting in crystal precipitation. Mutations in genes coding COLA transporter and the mode of inheritance were identified only in some canine breeds. Cystinuric dogs may form uroliths (mostly in lower urinary tract) which are associated with typical clinical symptoms. The prevalence of cystine urolithiasis is much higher in European countries (up to 14% according to the recent reports) when compared to North America (United States and Canada) where it is approximately 1-3%. Cystinuria may be diagnosed by the detection of cystine urolithiasis, cystine crystalluria, assessment of amino aciduria, or using genetic tests. The management of cystinuria is aimed at urolith removal or dissolution which may be reached by dietary changes or medical treatment. In dogs with androgen-dependent cystinuria, castration will help. In cats, cystinuria occurs less frequently in comparison with dogs.

Urolithiasis in dogs: Evaluation of trends in urolith composition and risk factors (2006-2018)

BACKGROUND

Urolithiasis is a common and often recurrent problem in dogs.

OBJECTIVE

To evaluate trends in urolith composition in dogs and to assess risk factors for urolithiasis, including age, breed, sex, neuter status, urolith location, and bacterial urolith cultures.

SAMPLE POPULATION

A total of 10 444 uroliths and the dogs from which they were obtained.

METHODS

The laboratory database at the UC Davis Gerald V. Ling Urinary Stone Analysis Laboratory was searched for all urolith submissions from dogs between January 2006 and December 2018. Mineral type, age, breed, sex, neuter status, urolith location, and urolith culture were recorded. Trends were evaluated and variables compared to evaluate risk factors.

RESULTS

Calcium oxalate (CaOx) and struvite-containing uroliths comprised the majority of all submissions from dogs, representing 47.0% and 43.6%, respectively. The proportion of CaOx-containing uroliths significantly decreased from 49.5% in 2006 to 41.8% in 2018 (P = .006), with no change in the proportion of struvite-containing urolith submissions. Cystine-containing uroliths comprised 2.7% of all submissions between 2006 and 2018 and a significant nonlinear increase in this mineral type occurred over time (1.4% of all submissions in 2006 to 8.7% in 2018; P < .001). Of all cystine-containing uroliths, 70.3% were from intact male dogs. Age, breed, and sex predispositions for uroliths were similar to those previously identified.

CONCLUSIONS AND CLINICAL IMPORTANCE

Although calcium oxalate- and struvite-containing uroliths continue to be the most common uroliths submitted from dogs, a decrease in the proportion of CaOx-containing uroliths and an increase in the proportion of cystine-containing uroliths occurred during the time period evaluated.

Analysis of 7866 feline and canine uroliths submitted between 2014 and 2020 in the Netherlands

Analysis of large datasets of uroliths is necessary to illustrate the prevalence and risk factors of urolithiasis. Furthermore, it may help to improve treatment and prevention of urolithiasis. In this study, 7866 uroliths (44.5% feline and 55.5% canine) from veterinary practitioners in the Netherlands between 2014 and 2020 were analysed. Between 2014 and 2020 the distribution over the different types of uroliths remained similar over time. Female cats, obese cats, Domestic Shorthair cats, female dogs, and large breed dogs had an increased risk for struvite. Neutered cats, all cat breeds except Domestic Shorthair, neutered dogs, male dogs, intact male dogs, and small breed dogs had an increased risk for calcium oxalate urolithiasis. Cystine and urate were found predominantly in male dogs. Dalmatians were at highest risk for urate urolithiasis. The findings of this study in the Netherlands were similar to findings in previous studies from different countries. However, urate urolithiasis in the English Cocker Spaniel and cystine urolithiasis in the Yorkshire Terrier were new associations. Body condition score, information about recurrence of urolithiasis, medical history, and diet history should be included in submission sheets in the future to explore other possible associations.

Calcium oxalate urolithiasis in juvenile dogs

BACKGROUND

The features of juvenile-onset calcium oxalate urolithiasis in dogs have not been previously reported.

METHODS

Calcium oxalate urolith submissions to the Minnesota Urolith Center between 2012 and 2016 were analyzed to identify those originating from juvenile (≤2 years, n = 510) or mature (7-9 years, n = 39,093) dogs. Breed, sex, urolith salt type and urolith location were compared between groups. Breeds represented in both groups were also compared with respect to sex, urolith salt type and urolith location.

RESULTS

French (odds ratios [OR] = 14.7, p < 0.001) and English (OR = 14.3, p < 0.001) Bulldogs were overrepresented in juvenile submissions. All juvenile French and English Bulldogs were male. Across all breeds, juvenile dogs were more likely to be male (89%, p < 0.001) than mature dogs (79%). Juvenile dogs were also more likely to form dihydrate stones compared to mature dogs (33% versus 14%, respectively; p < 0.001). Breed differences were discovered in sex, urolith salt type and stone location.

CONCLUSIONS

French and English Bulldogs comprise a greater proportion of juvenile calcium oxalate urolith submissions than expected based on their rarity in mature submissions. Inherited risk factors, particularly X chromosome variants, should be investigated due to the strong breed and sex predispositions identified.

Web resource on available DNA variant tests for hereditary diseases and genetic predispositions in dogs and cats: An Update

Vast progress has been made in the clinical diagnosis and molecular basis of hereditary diseases and genetic predisposition in companion animals. The purpose of this report is to provide an update on the availability of DNA testing for hereditary diseases and genetic predispositions in dogs and cats utilizing the WSAVA-PennGen DNA Testing Database web resource (URL: http://research.vet.upenn.edu/WSAVA-LabSearch ). Information on hereditary diseases, DNA tests, genetic testing laboratories and afflicted breeds added to the web-based WSAVA-PennGen DNA Testing Database was gathered. Following verification through original research and clinical studies, searching various databases on hereditary diseases in dogs and cats, and contacting laboratories offering DNA tests, the data were compared to the resource reported on in 2013. The number of molecularly defined Mendelian inherited diseases and variants in companion animals listed in the WSAVA-PennGen DNA Testing Database in 2020 drastically increased by 112% and 141%, respectively. The number of DNA variant tests offered by each laboratory has also doubled for dogs and cats. While the overall number of laboratories has only slightly increased from 43 to 47, the number of larger corporate laboratories increased, while academic laboratories have declined. In addition, there are now several laboratories that are offering breed-specific or all-breed panel tests rather than single-DNA tests for dogs and cats. This unique regularly updated searchable web-based database allows veterinary clinicians, breeders and pet owners to readily find available DNA tests, laboratories performing these DNA tests worldwide, and canine and feline breeds afflicted and also serves as a valuable resource for comparative geneticists.

Animal models of naturally occurring stone disease

The prevalence of urolithiasis in humans is increasing worldwide; however, non-surgical treatment and prevention options remain limited despite decades of investigation. Most existing laboratory animal models for urolithiasis rely on highly artificial methods of stone induction and, as a result, might not be fully applicable to the study of natural stone initiation and growth. Animal models that naturally and spontaneously form uroliths are an underused resource in the study of human stone disease and offer many potential opportunities for improving insight into stone pathogenesis. These models include domestic dogs and cats, as well as a variety of other captive and wild species, such as otters, dolphins and ferrets, that form calcium oxalate, struvite, uric acid, cystine and other stone types. Improved collaboration between urologists, basic scientists and veterinarians is warranted to further our understanding of how stones form and to consider possible new preventive and therapeutic treatment options.

Cystine Urolithiasis in Ferrets

Urolithiasis in captive domestic ferrets has previously been predominantly struvite uroliths, although more recent laboratory submissions show a shift to predominantly cystine uroliths. Genetic mutations for cystinuria have been identified in dogs, and it is suspected that underlying genetic mutations are partly responsible for this disease in ferrets. Currently, surgery remains the only definitive treatment of cystine urolithiasis in ferrets, since dietary dissolution protocols have not been thoroughly explored. Despite this, medical management with dietary and urinary manipulation should be considered for use in ferrets postoperatively based on principles of cystine urolithiasis management in dogs adapted for ferrets.

Cryo-EM structure of the human heteromeric amino acid transporter b0,+AT-rBAT

Heteromeric amino acid transporters (HATs) catalyze the transmembrane movement of amino acids, comprising two subunits, a heavy chain and a light chain, linked by a disulfide bridge. The b^0,+AT (SLC7A9) is a representative light chain of HATs, forming heterodimer with rBAT, a heavy chain which mediates the membrane trafficking of b^0,+AT. The b^0,+AT-rBAT complex is an obligatory exchanger, which mediates the influx of cystine and cationic amino acids and the efflux of neutral amino acids in kidney and small intestine. Here, we report the cryo-EM structure of the human b^0,+AT-rBAT complex alone and in complex with arginine substrate at resolution of 2.7 and 2.3 Å, respectively. The overall structure of b^0,+AT-rBAT exists as a dimer of heterodimer consistent with the previous study. A ligand molecule is bound to the substrate binding pocket, near which an occluded pocket is identified, to which we found that it is important for substrate transport.

Retained laser fiber in the nidus of a recurrent cystine urolith in an intact male English bulldog

A lithotripsy and percutaneous cystolithotomy (PCCL) were performed on a 5-year-old intact male English bulldog. The composition of the uroliths was 100% cystine. When a second PCCL was performed 2 months later, the nidus of the largest urolith was a segment of an optical fiber broken off during laser lithotripsy.

Amino acid transporters revisited: New views in health and disease

Amino acid transporters (AATs) are membrane-bound transport proteins that mediate transfer of amino acids into and out of cells or cellular organelles. AATs have diverse functional roles ranging from neurotransmission to acid-base balance, intracellular energy metabolism, and anabolic and catabolic reactions. In cancer cells and diabetes, dysregulation of AATs leads to metabolic reprogramming, which changes intracellular amino acid levels, contributing to the pathogenesis of cancer, obesity and diabetes. Indeed, the neutral amino acid transporters (NATs) SLC7A5/LAT1 and SLC1A5/ASCT2 are likely involved in several human malignancies. However, a clinical therapy that directly targets AATs has not yet been developed. The purpose of this review is to highlight the structural and functional diversity of AATs, their diverse physiological roles in different tissues and organs, their wide-ranging implications in human diseases and the emerging strategies and tools that will be necessary to target AATs therapeutically.

Frequency and distribution of 152 genetic disease variants in over 100,000 mixed breed and purebred dogs

Knowledge on the genetic epidemiology of disorders in the dog population has implications for both veterinary medicine and sustainable breeding. Limited data on frequencies of genetic disease variants across breeds exists, and the disease heritage of mixed breed dogs remains poorly explored to date. Advances in genetic screening technologies now enable comprehensive investigations of the canine disease heritage, and generate health-related big data that can be turned into action. We pursued population screening of genetic variants implicated in Mendelian disorders in the largest canine study sample examined to date by examining over 83,000 mixed breed and 18,000 purebred dogs representing 330 breeds for 152 known variants using a custom-designed beadchip microarray. We further announce the creation of MyBreedData (www.mybreeddata.com), an online updated inherited disorder prevalence resource with its foundation in the generated data. We identified the most prevalent, and rare, disease susceptibility variants across the general dog population while providing the first extensive snapshot of the mixed breed disease heritage. Approximately two in five dogs carried at least one copy of a tested disease variant. Most disease variants are shared by both mixed breeds and purebreds, while breed- or line-specificity of others is strongly suggested. Mixed breed dogs were more likely to carry a common recessive disease, whereas purebreds were more likely to be genetically affected with one, providing DNA-based evidence for hybrid vigor. We discovered genetic presence of 22 disease variants in at least one additional breed in which they were previously undescribed. Some mutations likely manifest similarly independently of breed background; however, we emphasize the need for follow up investigations in each case and provide a suggested validation protocol for broader consideration. In conclusion, our study provides unique insight into genetic epidemiology of canine disease risk variants, and their relevance for veterinary medicine, breeding programs and animal welfare.

Like any human, dogs may suffer from or pass on a variety of inherited disorders. Knowledge of how likely a typical dog is to carry an inherited disorder in its genome, and which disorders are the most common and relevant ones across dog breeds, is valuable for both veterinary care and breeding of healthy dogs. We have explored the largest global dog study sample collected to date, consisting of more than 100,000 mixed breed and purebred dogs, to advance research on this subject. We found that mixed breed dogs and purebred dogs potentially suffer from many of the same inherited disorders, and that around two in five dogs carried at least one of the conditions that we screened for. A dog carrying an inherited disorder is not a “bad dog”–but we humans responsible for breeding selections do need to make sustainable decisions avoiding inbreeding, i.e. mating of dogs that are close relatives. The disease prevalence information we generated during this study is made available online (www.mybreeddata.com), as a free tool for breed and kennel clubs, breeders, as well as the veterinary and scientific community.

PREVALENCE OF CYSTINURIA IN SERVALS ( LEPTAILURUS SERVAL) IN THE UNITED STATES

Cystinuria is a condition caused by defects in amino acid transport within the kidneys and small intestines. It has been reported in humans, dogs, domestic cats, ferrets, nondomestic canids, and nondomestic felids, including servals ( Leptailurus serval). Genetic mutations have been identified in dogs, humans, and domestic cats. Cystinuria usually follows an autosomal recessive inheritance, although it can be autosomal dominant and sex linked. The primary objective of this study was to screen urine samples dried on filter paper from captive servals in the United States for cystinuria by using the cyanide-nitroprusside screening test. A second objective was to determine whether cystinuria is inheritable in servals. Servals were initially recruited for the study by survey. Owners and institutions interested in participating were sent a second survey and filter paper for collecting urine samples. Samples were collected from 25 servals. One additional serval with confirmed cystine urolithiasis was added for a total sample size of 26 servals. Twenty-seven percent (7/26) were positive, 54% (14/26) were weakly positive, and 19% (5/26) were negative. Sex, reproductive status, and urine collection method had no significant association with test results. This condition is likely underreported in servals and should be ruled out in any serval with nonspecific signs of illness; neurologic signs such as lethargy, ataxia, or seizures; ptyalism; or signs of lower urinary tract disease such as dysuria, hematuria, stranguria, pollakiuria, or urethral obstructions.

Frequency of five disease-causing genetic mutations in a large mixed-breed dog population (2011-2012)

Background

A large and growing number of inherited genetic disease mutations are now known in the dog. Frequencies of these mutations are typically examined within the breed of discovery, possibly in related breeds, but nearly always in purebred dogs. No report to date has examined the frequencies of specific genetic disease mutations in a large population of mixed-breed dogs. Further, veterinarians and dog owners typically dismiss inherited/genetic diseases as possibilities for health problems in mixed-breed dogs, assuming hybrid vigor will guarantee that single-gene disease mutations are not a cause for concern. Therefore, the objective of this study was to screen a large mixed-breed canine population for the presence of mutant alleles associated with five autosomal recessive disorders: hyperuricosuria and hyperuricemia (HUU), cystinuria (CYST), factor VII deficiency (FVIID), myotonia congenita (MYC) and phosphofructokinase deficiency (PKFD). Genetic testing was performed in conjunction with breed determination via the commercially-available Wisdom Panel^TM test.

Results

From a population of nearly 35,000 dogs, homozygous mutant dogs were identified for HUU (n = 57) and FVIID (n = 65). Homozygotes for HUU and FVIID were identified even among dogs with highly mixed breed ancestry. Carriers were identified for all disorders except MYC. HUU and FVIID were of high enough frequency to merit consideration in any mixed-breed dog, while CYST, MYC, and PKFD are vanishingly rare.

Conclusions

The assumption that mixed-breed dogs do not suffer from single-gene genetic disorders is shown here to be false. Within the diseases examined, HUU and FVIID should remain on any practitioner’s rule-out list, when clinically appropriate, for all mixed-breed dogs, and judicious genetic testing should be performed for diagnosis or screening. Future testing of large mixed-breed dog populations that include additional known canine genetic mutations will refine our knowledge of which genetic diseases can strike mixed-breed dogs.

Effects of Lysine deficiency and Lys-Lys dipeptide on cellular apoptosis and amino acids metabolism

SCOPE

Lysine (Lys) is a common limiting amino acids (AA) for humans and animals and plays an important role in cell proliferation and metabolism, while metabolism of Lys deficiency and its dipeptide is still obscure. Thus, this study mainly investigated the effects of Lys deficiency and Lys-Lys dipeptide on apoptosis and AA metabolism in vitro and in vivo models.

METHODS AND RESULTS

Lys deficiency induced cell-cycle arrest and apoptosis and upregulated Lys transporters in vitro and in vivo. SLC7A11, a cystine-glutamate antiporter, was markedly upregulated by Lys deficiency and then further mediated cystine uptake and glutamate release, which was negatively regulated by cystine and glutamate transporters. Meanwhile, Lys deprivation upregulated pept1 expression, which might improve Lys-Lys dipeptide absorption to compensate for the reduced Lys availability. Lys-Lys dipeptide alleviated Lys deficiency induced cell-cycle arrest and apoptosis and influenced AA metabolism. Furthermore, the mammalian target of rapamycin signal might be involved in sensing cellular Lys starvation and Lys-Lys dipeptide.

CONCLUSIONS

Altogether, these studies suggest that Lys deficiency impairs AA metabolism and causes apoptosis. Lys-Lys dipeptide serves as a Lys source and alleviates Lys deficiency induced cellular imbalance.

Association between cystine urolithiasis and neuter status of dogs within the UK

OBJECTIVES

The objectives of the study were to examine the association between diagnosis of cystine urolithiasis and entire versus neutered status in male dogs and whether the strength of association varies among breeds.

MATERIALS AND METHODS

A previously reported canine urolithiasis database was used, documenting all urolith submissions to Hill's Pet Nutrition UK over a 10-year period. Uroliths were classified as cystine or non-cystine, and only male dogs with known neuter status were included in the analysis. Breeds of dog (and an additional crossbreed group), for which there was a minimum of 10 cystine urolith submissions, were analysed individually, with all other breeds combined together to form a reference group. Results were analysed using chi-squared and Fisher's exact tests. Logistic regression was used to assess associations between breed and neuter status and formation of cystine calculi.

RESULTS

In multiple breeds, dogs with cystine uroliths were significantly more likely to be entire than dogs forming other types of urolith. Being an entire male, regardless of breed, was associated with an increased risk of cystine urolithiasis (odds ratio=4·5; 95% confidence interval: 3·22 to 6·37; P<0·001).

CLINICAL SIGNIFICANCE

Increased odds of cystine formation in entire dogs supports further investigation of castration as a method to prevent cystine urolithiasis.

[Cystinuria caused by a SLC7A9 missense mutation in Siamese-crossbred littermates in Germany]

Cystinuria is caused by defective proximal renal tubular reabsorption of the amino acids cystine, ornithine, lysine, and arginine (COLA). The low solubility of cystine in mildly acidic urine may lead to the formation of urinary cystine crystals and uroliths. Much progress has been made recently in the diagnosis and understanding of cystinuria in companion animals. In cats, cystinuria affects equally both genders independent of neutering status and, despite being rare, already more cystinuria-causing mutations have been detected in cats compared to dogs. In this study a litter of Siamese-crossbred cats in Germany was assessed clinically for cystinuria and screened for mutations known to cause cystinuria in cats. An adult male castrated cat was presented with cystine crystalluria and calculi-related urinary obstruction and treated with perineal urethrostomy, cystotomy, and medical management. This cat and a neutered male littermate without evidence of urinary tract disease were found to be positive for cystine by urinary nitroprusside test, to have increased urinary COLA values and to be homozygous for the p.Val294Glu mutation in the SLC7A9 gene coding for b^0,+AT subunit of the b^0,+ renal COLA transporter. Another littermate was non-cystinuric and did not carry this mutation. The same SLC7A9 mutation was previously found in a Maine coon, a Sphinx and a medium-haired cat in North America suggesting a common ancestor and likely first widespread SLC7A9 mutation causing cystinuria in cats. Genetic screening for this mutation may offer a simple and precise mean to diagnose other cats for cystinuria and offer specific management.

Delineation of cystinuria in Saudi Arabia: A case series

BACKGROUND

Cystinuria is an inherited metabolic disease that is caused by defects in two genes, SLC3A1 and SLC7A9, which result in a renal reabsorptive defect of cystine and other dibasic amino acids, including ornithine, arginine, and lysine. Patients usually present with recurrent renal calculi and may develop renal impairment. Medical management includes high fluid intake and chelating agents. To the best of our knowledge, this is the first study describing cystinuria in Saudi Arabia.

METHODS

A retrospective chart review for cystinuria patients from the genetic and nephrology divisions between 2010 to 2015. All patients were investigated, diagnosed and treated at King Abdulaziz Medical City in Saudi Arabia.

RESULTS

Eight patients were identified from five unrelated families. The age of onset ranged from birth to 14 years. The female to male ratio was 1.7:1. Two new variants in the SLC3A1 and SLC9A7 genes were discovered. All of the detected mutations were missense variants in three different exons, such as c.1711 T > A (p.Cys571Ser) (exon 10), c.1166C > T p.Thr389Met (exon 11) and c.1400 T > A p.Met467Lys (exon 8). Additionally, 37.5% of our patients developed arterial hypertension and 25% had urinary tract infection, but none had renal impairment. No significant clinical differences were detected in this study between type A (SLC3A1 variants) and type B cystinuria (SLC7A9 variant). Two cases were diagnosed based on clinical information, biochemical testing and a positive family history as all of the molecular testing for cystinuria was negative.

CONCLUSION

Cystinuria has wide genetic heterogeneity with a poor genotype/phenotype correlation. Negative molecular investigations should not rule out the disease if clinical and biochemical investigations support the diagnosis. A larger data registry is essential to better describe the cystinuria genotype/phenotype in Saudi Arabia.

Analysis of canine urolith submissions to the Canadian Veterinary Urolith Centre, 1998-2014

Understanding urolith trends and risk factors is important for understanding urolithiasis, which is a common problem in dogs. This study evaluated 75 674 canine cystolith submissions to the Canadian Veterinary Urolith Centre between 1998 and 2014. Struvite and calcium oxalate uroliths comprised 80.8% of all uroliths, with calcium oxalate outnumbering struvite. There were significant increases in the proportions of calcium oxalate, mixed and cystine uroliths, and significant decreases in struvite, urate, silica, and calcium phosphate carbonate over the study period. Breeds associated with increased risk of calcium oxalate urolithiasis tended to be small breeds, while those that were at increased risk of struvite urolith formation were larger breeds. Dalmatians were at increased risk of forming both urate and xanthine uroliths while Scottish deerhounds had a remarkably high association with cystine urolithiasis. Males were more likely to form calcium oxalate and metabolic uroliths and females were more likely to develop struvite and mixed uroliths.

ACVIM Small Animal Consensus Recommendations on the Treatment and Prevention of Uroliths in Dogs and Cats

In an age of advancing endoscopic and lithotripsy technologies, the management of urolithiasis poses a unique opportunity to advance compassionate veterinary care, not only for patients with urolithiasis but for those with other urinary diseases as well. The following are consensus-derived, research and experience-supported, patient-centered recommendations for the treatment and prevention of uroliths in dogs and cats utilizing contemporary strategies. Ultimately, we hope that these recommendations will serve as a foundation for ongoing and future clinical research and inspiration for innovative problem solving.

Genetic Panel Screening of Nearly 100 Mutations Reveals New Insights into the Breed Distribution of Risk Variants for Canine Hereditary Disorders

Background

The growing number of identified genetic disease risk variants across dog breeds challenges the current state-of-the-art of population screening, veterinary molecular diagnostics, and genetic counseling. Multiplex screening of such variants is now technologically feasible, but its practical potential as a supportive tool for canine breeding, disease diagnostics, pet care, and genetics research is still unexplored.

Results

To demonstrate the utility of comprehensive genetic panel screening, we tested nearly 7000 dogs representing around 230 breeds for 93 disease-associated variants using a custom-designed genotyping microarray (the MyDogDNA® panel test). In addition to known breed disease-associated mutations, we discovered 15 risk variants in a total of 34 breeds in which their presence was previously undocumented. We followed up on seven of these genetic findings to demonstrate their clinical relevance. We report additional breeds harboring variants causing factor VII deficiency, hyperuricosuria, lens luxation, von Willebrand’s disease, multifocal retinopathy, multidrug resistance, and rod-cone dysplasia. Moreover, we provide plausible molecular explanations for chondrodysplasia in the Chinook, cerebellar ataxia in the Norrbottenspitz, and familiar nephropathy in the Welsh Springer Spaniel.

Conclusions

These practical examples illustrate how genetic panel screening represents a comprehensive, efficient and powerful diagnostic and research discovery tool with a range of applications in veterinary care, disease research, and breeding. We conclude that several known disease alleles are more widespread across different breeds than previously recognized. However, careful follow up studies of any unexpected discoveries are essential to establish genotype-phenotype correlations, as is readiness to provide genetic counseling on their implications for the dog and its breed.

Cystinuria Associated with Different SLC7A9 Gene Variants in the Cat

Cystinuria is a classical inborn error of metabolism characterized by a selective proximal renal tubular defect affecting cystine, ornithine, lysine, and arginine (COLA) reabsorption, which can lead to uroliths and urinary obstruction. In humans, dogs and mice, cystinuria is caused by variants in one of two genes, SLC3A1 and SLC7A9, which encode the rBAT and bo,+AT subunits of the bo,+ basic amino acid transporter system, respectively. In this study, exons and flanking regions of the SLC3A1 and SLC7A9 genes were sequenced from genomic DNA of cats (Felis catus) with COLAuria and cystine calculi. Relative to the Felis catus-6.2 reference genome sequence, DNA sequences from these affected cats revealed 3 unique homozygous SLC7A9 missense variants: one in exon 5 (p.Asp236Asn) from a non-purpose-bred medium-haired cat, one in exon 7 (p.Val294Glu) in a Maine Coon and a Sphinx cat, and one in exon 10 (p.Thr392Met) from a non-purpose-bred long-haired cat. A genotyping assay subsequently identified another cystinuric domestic medium-haired cat that was homozygous for the variant originally identified in the purebred cats. These missense variants result in deleterious amino acid substitutions of highly conserved residues in the bo,+AT protein. A limited population survey supported that the variants found were likely causative. The remaining 2 sequenced domestic short-haired cats had a heterozygous variant at a splice donor site in intron 10 and a homozygous single nucleotide variant at a branchpoint in intron 11 of SLC7A9, respectively. This study identifies the first SLC7A9 variants causing feline cystinuria and reveals that, as in humans and dogs, this disease is genetically heterogeneous in cats.

Canine cystine urolithiasis: A review of 1760 submissions over 35 years (1979-2013)

This study reports a retrospective evaluation of epidemiological data from cystine stones of dogs submitted to the Urinary Stone Analysis Center Bonn, Germany, over a period of 35 years. Of the 20 316 uroliths submitted from 1979 to 2013, 1760 were cystine stones. In total, 109 breeds were affected with 16 breeds having an odds ratio > 1.0. Most of the cystine uroliths were retrieved from male dogs, with only 19 female dogs (1.1%) being affected. Percentage of submitted cystine stones amongst all stones decreased significantly over 35 years from 38.9% to 4.4%.

Feline cystinuria caused by a missense mutation in the SLC3A1 gene

Background

Cystinuria is an inherited metabolic disease that is relatively common in dogs, but rare in cats and is characterized by defective amino acid reabsorption, leading to cystine urolithiasis.

Objectives

The aim of this study was to report on a mutation in a cystinuric cat.

Animals

A male domestic shorthair (DSH) cat with cystine calculi, 11 control cats from Wyoming, and 54 DSH and purebred control cats from elsewhere in the United States.

Methods

Exons of the SLC3A1 gene were sequenced from genomic DNA of the cystinuric cat and a healthy cat. Genetic screening for the discovered polymorphisms was conducted on all cats.

Results

A DSH cat showed stranguria beginning at 2 months of age, and cystine calculi were removed at 4 months of age. The cat was euthanized at 6 months of age because of neurological signs possibly related to arginine deficiency. Twenty‐five SLC3A1 polymorphisms were observed in the sequenced cats when compared to the feline reference sequence. The cystinuric cat was homozygous for 5 exonic and 8 noncoding SLC3A1 polymorphisms, and 1 of them was a unique missense mutation (c.1342C>T). This mutation results in a deleterious amino acid substitution (p.Arg448Trp) of a highly conserved arginine residue in the rBAT protein encoded by the SLC3A1 gene. This mutation was found previously in cystinuric human patients, but was not seen in any other tested cats.

Conclusions and Clinical Importance

This study is the first report of an SLC3A1 mutation causing cystinuria in a cat, and could be used to characterize other cystinuric cats at the molecular level.