Krabbe disease or globoid cell leukodystrophy (GLD) is an autosomal recessive disorder resulting from the defective lysosomal hydrolysis of specific galactolipids found primarily in myelin. This leads to severe neurological symptoms including seizures, hypotonia, blindness, and death, usually before 2 years of age in human patients. In addition to human patients, several animals, including dog, mouse, and monkey, have the same disease caused by a deficiency of galactocerebrosidase (GALC) activity. In this article we describe studies in cairn and West Highland white terriers (WHWT) affected with GLD. Through a screening test based on the molecular defect found in these breeds, over 50 cairn terrier carriers have been identified and a colony of five carrier dogs has been established. Affected dogs from this colony plus an affected WHWT were available for study. An affected WHWT was evaluated by magnetic resonance imaging at 6 and 11 months of age and pronounced changes in the T-2 weighted fast spin-echo images were found. Biochemical and pathological evaluation of the same dog after euthanasia at 12 months of age showed a large accumulation of psychosine in the brain and white matter filled with globoid cells. Some comparisons were made to younger affected and carrier dogs. Studies have shown successful transduction of cultured skin fibroblasts from an affected dog and normal canine bone marrow using a retroviral vector containing the human GALC cDNA. Successful treatment of this canine model will lead to studies in some humans with GLD.

Globoid cell leukodystrophy (GLD), or Krabbe disease, is an inherited, neurologic disorder that results from deficiency of a lysosomal enzyme, galactosylceramidase. Most commonly, deficits of galactosylceramidase result in widespread central and peripheral nervous system demyelination and death in affected infants typically by 2 years of age. Hematopoietic stem-cell transplantation is the current standard of care in children diagnosed prior to symptom onset. However, disease correction is incomplete. Herein, the first adeno-associated virus (AAV) gene therapy experiments are presented in a naturally occurring canine model of GLD that closely recapitulates the clinical disease progression, neuropathological alterations, and biochemical abnormalities observed in human patients. Adapted from studies in twitcher mice, GLD dogs were treated by combination intravenous and intracerebroventricular injections of AAVrh10 to target both the peripheral and central nervous systems. Combination of intravenous and intracerebroventricular AAV gene therapy had a clear dose response and resulted in delayed onset of clinical signs, extended life-span, correction of biochemical defects, and attenuation of neuropathology. For the first time, therapeutic effect has been established in the canine model of GLD by targeting both peripheral and central nervous system impairments with potential clinical implications for GLD patients.

The avian retroviruses reticuloendotheliosis virus strain A (REV-A) and spleen necrosis virus (SNV) are not naturally infectious in human cells. However, REV-A-derived viral vectors efficiently infect human cells when they are pseudotyped with envelope proteins displaying targeting ligands specific for human cell-surface receptors. Here we report that vectors containing the gag region of REV-A and pol of SNV can be pseudotyped with the envelope protein of vesicular stomatitis virus (VSV) and the glycoproteins of different rabies virus (RV) strains. Vectors pseudotyped with the envelope protein of the highly neurotropic RV strain CVS-N2c facilitated cell type-specific gene delivery into mouse and human neurons, but did not infect other human cell types. Moreover, when such vector particles were injected into the brain of newborn mice, only neuronal cells were infected in vivo. Cell-type-specific gene delivery into neurons may present quite specific gene therapy approaches for many degenerative diseases of the brain.