EQUINE GLUCOSE-6-PHOSPHATE-DEHYDROGENASE DEFICIENCY

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a well-characte rized X-linked inherited disorder in humans but has not been reported in horses. We describe a persistent hemolytic anemia and hyperbilirubi nemia due to a severe G6PD deficiency in an American Saddlebred colt. Other abnormalities in the colt's erythrocytes as compared with those of healthy horses (n = 22-35) included increased activities of hexokin ase and pyruvate kinase, decreased concentrations of reduced glutathio ne and reduced nicotinamide adenine dinucleotide phosphate (NADP), and increased concentration of oxidized NADP. Morphologic abnormalities i ncluded eccentrocytosis, pyknocytosis, anisocytosis, macrocytosis, and increased number of Howell-Jolly bodies. Scanning and transmission el ectron microscopic examinations revealed that eccentrocytes had contra cted to spherical regions and thin collapsed regions. Eccentrocytes we re more electron dense than were normal erythrocytes when examined by transmission electron microscopy. When exposed to acetylphenylhydrazin e, erythrocytes from the G6PD-deficient colt produced more and smaller Heinz bodies than did erythrocytes from normal horses. Abnormalities in the colt's dam included presence of eccentrocytes and pyknocytes; h er average erythrocyte G6PD activity was slightly below the range of r eference values.