888. Characterization of New Murine Models of Globoid Cell Leukodystrophy: Relevance for Gene Therapy Applications and Studies on Disease Pathogenesis

Abstract

The Twitcher mouse (twi) is well known as a naturally occurring authentic mouse model of human globoid cell leukodystrophy (GLD), characterized by a stop mutation leading to complete deficiency of galactocerebrosidase (GALC) activity. The most commonly used twi mouse is on the C57BL/6J genetic background. Two novel murine models of GLD are currently available beside the original twi: i) the twi crossed into a different genetic background (FVB-Twi), that we generated based on previous indications on the effects of the genetic background in modulating GLD severity (Tominaga K. et al., J. Neurosci. Res. 2004; Biswas S. et al., Neurobiol. of Disease 2002); ii) a mouse with low GALC activity, recently generated in D. Wenger's laboratory by introducing in the murine GALC gene a polymorphism that was found in individuals having some not otherwise explainable neurological abnormalities in the presence of 10|[ndash]|20% residual GALC activity, the trs mouse (Luzi P. et al., Mol. Genetics and Metab. 2001). These three models showed some substantial differences in their phenotype and overall survival, and represent a unique opportunity not only to evaluate gene therapy efficacy in a wider therapeutic window, but also to better investigate disease pathogenesis. We characterized these new models in comparison with the C57BL/6J twi by longitudinal clinical, neurophysiological, neuroradiological and pathological evaluations. FVB-Twi and trs mice have a slightly milder phenotype as compared to original twi, with higher body weight, later onset of twitching, a delayed decline in walking ability, as measured by footprint analysis, longer life span (38|[plusmn]|2, 43|[plusmn]|2 and 56|[plusmn]|4 days in twi, FVB-Twi and trs, respectively), and better general health conditions. Despite the slower progression of the disease, neurophysiological studies showed a severe impairment of motor conduction along both central and peripheral nervous system, with profound reduction of motor conduction velocity (below 8m/sec) and un-evocable MEPs by 30 post-natal days of age in all examined models. Conventional brain MR imaging and histopathology showed lower grade demyelination in FVB-Twi and trs as compared to C57Bl/6 twi, and on going MR diffusion studies will provide quantification of the brain myelin content in the 3 different models. Overall, our data demonstrate the availability of new murine models of GLD characterized by a delayed demyelination as compared to the original twi mutants, that will constitute a precious tool for identifying the best timing of intervention to achieve correction of the GLD phenotype with gene therapy.