Glycosphingolipid β galactosidases. III. Canine form of globoid cell leukodystrophy; comparison with the human disease

Liver specimens of dogs affected with the canine form of globoid cell leukodystrophy were assayed for activities of specific glycosphingolipid β galactosidases. As in the human disease, activities of galactosylceramide and galactosylsphingosine β galactosidases were deficient in 3 homozygous affected dogs, while lactosylceramide, G(M1) ganglioside and asialo G(M1) ganglioside β galactosidases were normal. Upon electrofocusing, the livers of the affected dogs totally lacked the normal major galactosylceramide β galactosidase peak at an isoelectric point of 5.4 to 5.5 and the minor peak at pH 5.8 to 6.0. A suspected carrier dog showed an intermediate activity of the major enzyme peak. However, another peak of galactosylceramide β galactosidase at pH 5.0 to 5.1 was relatively preserved in the affected dogs, and it was only slightly less than normal in the carrier dog. Corresponding to these findings, the sharp peak at pH 5.4 to 5.5 of 4 methylumbelliferyl β galactosidase was almost absent in affected dogs and was partially deficient in the heterozygous dog, while 2 other peaks were normal. Electrofocusing patterns of lactosylceramide and asialo G(M1) ganglioside β galactosidases were completely normal in affected dogs. The peak of 4 methylumbelliferyl β galactosidase at pH 5.4 to 5.5 was not associated with the latter 2 sphingolipid β galactosidase activities. Therefore, the 4 methylumbelliferyl β galactosidase peak at pH 5.4 to 5.5 appears to represent one of the 2 major components of galactosylceramide β galactosidase, which is primarily defective in the canine form of globoid cell leukodystrophy. The human and canine forms of the disease can be considered equivalent to the extent that both are caused by genetic deficiency of galactosylceramide and galactosylsphingosine β galactosidases, but they are clearly different in the nature of the mutations underlying the defective enzymes.