Tremors in Samoyed pups with oligodendrocyte deficiencies and hypomyelination.

Over a 3-year period a breeder of Samoyed dogs observed six litters in which one or more pups at 3 weeks of age showed generalized tremors and an inability to stand. One affected pup, a 5-week-old male, was referred for clinical and pathological evaluation. Gross and microscopic studies including immunocytochemical demonstration of myelin basic protein, revealed a lack of myelin throughout the central nervous system. Ultrastructural studies revealed that a total absence of normal myelin was associated with oligodendroglial deficiencies. Oligodendrocytes were immature in appearance, greatly reduced in number, and incapable of forming compact myelin. Astrocytosis and an increase in the third type of neuroglial cells were observed. The changes differed from those reported in other canine forms of hypomyelinogenesis and were compared with hypomyelinating diseases in other species. The findings suggested that this hypomyelination was the result of retarded gliogenesis.