Abstract
Progressive dysmetria was observed at four months and six months of age in two female Labrador retriever littermates. Neurological examinations indicated a cerebellar disorder. Laboratory analyses were normal. The dogs were studied clinically until they were killed for necropsy at nine months and eleven months of age. Both dogs had normal brain size, shape, and calvarial symmetry; the older dog had body weight loss, reduced brain weight, and muscle atrophy. Microscopically, there were vacuoles, hypertrophied fibrous astrocytes, myelin loss, and prominent blood vessels, distributed symmetrically in the subcortical and deep white matter of all lobes of the cerebrum; in the folial and deep white matter of the cerebellum; in the tracts of some cranial nerves; in the thalamic area, midbrain and brainstem; and in the white matter of the spinal cord. There was no significant myelinolysis, inflammation, or axonal degeneration. Ultrastructurally, there were intramyelinic vacuoles with separation of lamellae at intraperiod lines and larger spaces formed by coalescence of ruptured vacuoles. Hypertrophied fibrous astrocytes had abundant glial filaments, edematous cytosol, membrane-bound crystalline inclusions, dilated cytocavitary systems, and abnormal mitochondria. The clinical, histological, and ultrastructural findings resembled those reported for the juvenile form of Canavan's disease (van Bogaert and Bertrand type) in children.