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Idiopathic hypocalcemia in Thoroughbred (TB) foals causes tetany and seizures and is invariably fatal. Based upon the similarity of this disease with human familial hypoparathyroidism and occurrence only in the TB breed, we conducted a genetic investigation on two affected TB foals. Familial hypoparathyroidism was identified, and pedigree analysis suggested an autosomal recessive (AR) mode of inheritance. We performed whole-genome sequencing of the two foals, their unaffected dams and four unaffected, unrelated TB horses. Both homozygosity mapping and an association analysis were used to prioritize potential genetic variants. Of the 2,808 variants that significantly associated with the phenotype using an AR mode of inheritance (PA,p.Ser875*) was significantly associated with the hypoparathyroid phenotype (Pallelic = 0.008). Affected foals were homozygous for the variant, with two additional affected foals subsequently confirmed in 2019. Necropsies of all affected foals failed to identify any histologically normal parathyroid glands. Because the nonsense mutation in RAPGEF5 was near the C-terminal end of the protein, the impact on protein function was unclear. Therefore, we tested the variant in our Xenopus overexpression model and demonstrated RAPGEF5 loss-of-function. This RAPGEF5 variant represents the first genetic variant for hypoparathyroidism identified in any domestic animal species.

A letter to the editor is presented regarding a one-year old Quarter Horse colt with a six-month history of nasal discharge and respiratory noise.

Objective:  The aim of this study was to evaluate the functional, systemic, synovial and articular changes after intra-articular administration of a synthetic lubricin within healthy canine stifles., Study Design:  A prospective randomized blinded placebo-controlled study composed of 10 dogs equally divided into either a treatment group (intra-articular synthetic lubricin injection, n  = 5) or control group (saline, n  = 5). Clinical (orthopaedic examination, gait observation, gait analysis), biochemical (complete blood count and biochemistry profile) and local tissue outcomes (joint fluid analysis, joint capsule and articular cartilage histopathology) were evaluated over a time period of 3 months., Results:  No significant differences between the treatment group and control group were identified with regard to baseline patient parameters. No clinically significant orthopaedic examination abnormalities, gait abnormalities, biochemical alterations, joint fluid alterations or histopathological alterations were identified over the course of the study., Conclusion:  The synthetic lubricin studied herein is both biocompatible and safe for a single administration within the canine stifle joint. Further research is necessary to evaluate the clinical efficacy of the synthetic lubricin in canine osteoarthritic joints., Competing Interests: D.P. is listed as an inventor on various patents assigned to Cornell University that are associated with materials disclosed in this manuscript. There is no financial or other conflict of interest of any author related to a company or product used in the report. This study was never presented at any meetings., (Thieme. All rights reserved.)

Objective:  The purpose of this observational study was to establish normative data for the canine menisci using magnetic resonance imaging (MRI)., Methods:  Ten fresh stifles from five normal male Beagles were obtained from animals with no known lameness. Conventional MRI and ultrashort echo time (UTE) imaging were performed and T 2 * values calculated. Five stifles were assessed histologically., Results:  The caudal horn of the medial meniscus had significantly prolonged T 2 * values (4.6 ± 1.27 ms; p  = 0.002) as compared with the cranial horn of the medial meniscus (3.25 ± 0.86 ms), and the cranial (3.06 ± 0.54 ms) and caudal (3.64 ± 0.72 ms) horns of the lateral meniscus. Histology demonstrated normal tibial, femoral, interior and peripheral meniscal margins, and normal cellularity. The medial meniscus was noted to be obliquely oriented to the scan plane compared with the relatively perpendicular orientation of the lateral meniscus as compared with the bore of the magnet in a limb-extended orientation., Clinical Significance:  Variability of MRI UTE T 2 * is seen in the normal canine meniscus, with prolongation of the caudal horn, medial meniscus. Prolongation may be due to magic angle effects, as the medial meniscus of the Beagle is not perpendicular to the axis of the main magnetic field. Canine meniscal injury is a common sequela to cruciate tear, and detecting meniscal damage is important for directing patient care. The non-invasive quantitative MRI technique of UTE imaging can be used for the evaluation of collagen orientation, while acknowledging inherent regions of prolongation., Competing Interests: None of the authors of this article have a financial or personal relationship with other individuals or organizations which could inappropriately influence or bias the content of this article., (Georg Thieme Verlag KG Stuttgart · New York.)

Objectives:  The purpose of this study was to evaluate regional differences of canine stifle articular cartilage using the quantitative magnetic resonance imaging (MRI) technique of T2 mapping., Methods:  Fourteen stifle joints from seven juvenile male Beagle dogs with no evidence or prior history of pelvic limb lameness were imaged ex vivo using standard of care fast spin echo MRI and quantitative T2 mapping protocols. Regions of interest were compared between the femoral, patellar and tibial cartilages, as well as between the lateral and medial femorotibial compartments. Limbs were processed for histology with standard stains to confirm normal cartilage., Results:  The average T2 value of femoral trochlear cartilage (37.5 ± 2.3 ms) was significantly prolonged ( p  < 0.0001) as compared with the femoral condylar, patellar and tibial condylar cartilages (33.1 ± 1.5 ms, 32.8 ± 2.3 ms, and 28.0 ± 1.7 ms, respectively). When comparing medial and lateral condylar compartments, the lateral femoral condylar cartilage had the longest T2 values (34.8 ± 2.8 ms), as compared with the medial femoral condylar cartilage (30.9 ± 1.9 ms) and lateral tibial cartilage (29.1 ± 2.3 ms), while the medial tibial cartilage had the shortest T2 values (26.7 ± 2.4 ms)., Clinical Significance:  As seen in other species, regional differences in T2 values of the canine stifle joint are identified. Understanding normal regions of anticipated prolongation in different joint compartments is needed when using quantitative imaging in models of canine osteoarthritis., Competing Interests: HSS MRI Laboratory receives institutional research support from General Electric Healthcare; however, no funding was provided for this study. None of the authors of this article have a financial or personal relationship with other individuals or organizations which could inappropriately influence or bias the content of this paper., (Schattauer GmbH Stuttgart.)