Joshua A. Stern

Background Glanzmann's thrombasthenia (GT) is a congenital platelet disorder affecting approximately 1:1 000 000 people globally and characterized by impaired platelet aggregation and clot retraction. Autosomal recessive, loss‐of‐function, variants in ITGA2B or ITGB3 of the αIIbβ3 receptor cause the disease in humans. A cat affected by Glanzmann's and macrothrombocytopenia was presented to the UC Davis VMTH. Hypothesis/Objectives Severe thrombopathia in this cat has an underlying genetic etiology. Animals A single affected patient, 2 age‐matched clinically healthy controls, and a geriatric population (n = 20) of normal cats. Methods Physical examination and clinical pathology tests were performed on the patient. Flow cytometry and platelet aggregometry analyses for patient phenotyping were performed. Patient and validation cohort gDNA samples were extracted for Sanger sequencing of a previously identified ITGA2B (c.1986delC) variant. Reverse transcriptase PCR was performed on patient and healthy control PRP samples to verify ITGA2B variant consequence. Results A novel c.1986_1987insCC autosomal recessive variant in ITGA2B was identified. This variant was absent in a population of 194 unrelated cats spanning 44 different breeds. Complete loss of ITGA2B transcript and protein expression was verified by RT‐PCR and flow cytometry, explaining the underlying etiology of GT, and likely macrothrombocytopenia, in this cat. Conclusions and Clinical Importance This study emphasizes the role of precision medicine in cardiovascular disease of cats and identified yet another variant that may be of utility for screening in the feline population. This study provides a small‐volume, standardized, successful protocol for adequate platelet RNA isolation and subsequent molecular assessment of gene expression in cats.

Hypertrophic cardiomyopathy (HCM) remains the single most common cardiomyopathy in cats, with a staggering prevalence as high as 15%. To date, little to no direct therapeutical intervention for HCM exists for veterinary patients. A previous study aimed to evaluate the effects of delayed-release (DR) rapamycin dosing in a client-owned population of subclinical, non-obstructive, HCM-affected cats and reported that the drug was well tolerated and resulted in beneficial LV remodeling. However, the precise effects of rapamycin in the hypertrophied myocardium remain unknown. Using a feline research colony with naturally occurring hereditary HCM (n = 9), we embarked on the first-ever pilot study to examine the tissue-, urine-, and plasma-level proteomic and tissue-level transcriptomic effects of an intermittent low dose (0.15 mg/kg) and high dose (0.30 mg/kg) of DR oral rapamycin once weekly. Rapamycin remained safe and well tolerated in cats receiving both doses for eight weeks. Following repeated weekly dosing, transcriptomic differences between the low- and high-dose groups support dose-responsive suppressive effects on myocardial hypertrophy and stimulatory effects on autophagy. Differences in the myocardial proteome between treated and control cats suggest potential anti-coagulant/-thrombotic, cellular remodeling, and metabolic effects of the drug. The results of this study closely recapitulate what is observed in the human literature, and the use of rapamycin in the clinical setting as the first therapeutic agent with disease-modifying effects on HCM remains promising. The results of this study establish the need for future validation efforts that investigate the fine-scale relationship between rapamycin treatment and the most compelling gene expression and protein abundance differences reported here.