Stomatocytosis in 7 related Standard Schnauzers

Background: Hereditary canine stomatocytosis has been described in purebred Alaskan Malamutes, Drentse Patrijshonds, and Miniature Schnauzers. In humans, hereditary stomatocytosis is a heterogeneous group of congenital disorders characterized by the presence of stomatocytes in blood, increased osmotic fragility, and frequently, hemolytic anemia. Objective: Our objective was to describe hematologic findings and RBC characteristics in 7 closely related Standard Schnauzers with stomatocytosis. Methods: The following parameters were measured using an automated analyzer: HCT, RBC, hemoglobin (Hb) concentration, MCV, MCH, MCHC, red cell distribution width (RDW), WBC, platelet count, mean platelet volume (MPV), thrombocrit (PCT), and platelet distribution width (PDW). Differential leukocyte count, platelet estimate, reticulocyte count, and the percentage of stomatocytes in blood films were microscopically evaluated. An osmotic fragility test of RBCs and measurement of intracellular Na+, K+, and 2,3-diphosphoglycerate (2,3-DPG) concentrations were also performed. Results: The affected dogs had macrocytosis (80.0 ± 4.2 fL, reference interval 60-76 fL), decreased MCHC (29.3 ± 0.8 g/dL, reference interval 32-39 g/dL), slightly increased RDW (17.3 ± 0.4%, reference interval 12-16%), and an increased reticulocyte count (1.55 ± 0.77%, reference interval <1%). The percentage of stomatocytes in blood films varied from 0.6 to 18.9% of all RBCs. Erythrocyte osmotic fragility and intracellular Na+ (138.1 ± 3.2 mmol/L; controls 99 ± 6.1 mmol/L), K+ (8.1 ± 0.8 mmol/L; controls 6.1 ± 0.5 mmol/L), and 2,3-DPG (21.9 ± 2.0 μmol/g Hb; controls: 14.6 ± 3.3 μmol/g Hb) concentrations were increased in dogs with stomatocytosis. Conclusions: Hematologic findings and the metabolic defects in RBCs in these Standard Schnauzers were consistent with a diagnosis of stomatocytosis. Parentage analysis suggests that stomatocytosis in Standard Schnauzers may have a hereditary component.