Hypomyelination in Weimaraner dogs.

Dogs from two separate litters of Weimaraners developed tremors by 3 weeks of age. Light and electron microscopic findings in one dog from each of the litters were compared to those of two age-matched controls. Many axons in the brain and spinal cord were either thinly myelinated or nonmyelinated in the affected dogs relative to the controls, while the peripheral nervous system was normally myelinated. The degree of hypomyelination seemed particularly severe at the periphery of the lateral and ventral funiculi of the spinal cord. In all areas of white matter evaluated, astrocytes subjectively outnumbered oligodendrocytes in the Weimaraners, while the reverse was true in the controls. This discrepancy in oligodendrocyte and astrocyte numbers was confirmed quantitatively in the spinal cord. These findings suggested that abnormal glial differentiation was responsible for the hypomyelination. Clinical signs in two affected littermates of one of the dogs gradually resolved, suggesting that the underlying lesion was reversible.