Toward the most ideal case-control design with related and unrelated dogs in whole-exome sequencing studies.

With the recent development of whole-exome sequencing enrichment designs for the dog, a novel tool for disease-association studies became available. The aim of disease-association studies is to identify one or a very limited number of putative causal variants or genes from the large pool of genetic variation. To maximize the efficiency of these studies and to provide some directions of what to expect, we evaluated the effect on variant reduction for various combinations of cases and controls for both dominant and recessive types of inheritance assuming variable degrees of penetrance and detectance. In this study, variant data of 14 dogs (13 Labrador Retrievers and one Dogue de Bordeaux), obtained by whole-exome sequencing, were analyzed. In the filtering process, we found that unrelated dogs from the same breed share up to 70% of their variants, which is likely a consequence of the breeding history of the dog. For the designs tested with unrelated dogs, combining two cases and two controls gave the best result. These results were improved further by adding closely related dogs. Reduced penetrance and/or detectance has a drastic effect on the efficiency and is likely to have a profound effect on the sample size needed to elucidate the causal variant. Overall, we demonstrated that sequencing a small number of dogs results in a marked reduction of variants that are likely sufficient to pinpoint causal variants or genes.

Screening of ragdoll cats for kidney disease: a retrospective evaluation.

OBJECTIVES: To assess the prevalence of renal abnormalities in ragdoll cats. Ragdoll breeders often warn clients to watch for future renal problems, mainly due to chronic interstitial nephritis and polycystic kidney disease. Therefore, ragdoll screening by abdominal ultrasonography, measurement of serum creatinine and urea concentrations and genetic testing is often performed without documented scientific evidence of increased risk of renal disease. METHODS: Retrospective evaluation of ragdoll screening for renal disease at one institution over an eight-year period. RESULTS: Renal ultrasonography was performed in 244 healthy ragdoll cats. Seven cats were positive for polycystic kidney disease, 21 were suspected to have chronic kidney disease, 8 had abnormalities of unknown significance and 2 cats had only one visible kidney. Cats suspected to have chronic kidney disease were significantly older and had significantly higher serum urea and creatinine concentrations than cats with normal renal ultrasonography. All 125 genetically tested cats were negative for polycystic kidney disease. However, only one of the seven ultrasonographically positive cats underwent genetic testing for polycystic kidney disease. CLINICAL SIGNIFICANCE: Ultrasonographic findings compatible with chronic kidney disease were observed in almost 10% of cats, and polycystic kidney disease occurred at a low prevalence (<3%) in this ragdoll population. Further studies are required to elucidate if ragdoll cats are predisposed to chronic kidney disease.

Inspiratory stridor secondary to palatolingual myokymia in a Maltese dog.

A nine-year-old male Maltese dog was presented with an eight-month history of inspiratory stridor leading to exertional dyspnoea and cyanosis. Myokymic contractions in the palatolingual muscles were noticed and confirmed by electromyography. Brain computer tomography-scan showed ventricular dilatation. Cerebrospinal fluid analysis revealed a slightly elevated protein level. Treatment with slow-release phenytoin was unsuccessful and symptoms gradually worsened over the next nine months. At post-mortem examination a small pituitary adenoma was found. Apart from a single canine report of facial myokymia, this is the only other description of spontaneous focal myokymia in animals. Palatolingual myokymia has only been reported in one human being. Although the co-occurrence with a pituitary adenoma might be incidental, a paraneoplastic pathogenetic mechanism is proposed. Its unique clinical presentation adds a new, albeit uncommon, syndrome to the differential diagnosis of upper airway complaints in dogs.