In Niemann-Pick C1 mouse models, glial-only expression of the normal gene extends survival much further than do changes in genetic background or treatment with hydroxypropyl-beta-cyclodextrin

The Npc1nmf164 allele of Npc1 provides a mouse model for Niemann-Pick disease type C1 (NPC1), a genetic disease known to have a widely variable phenotype. The transfer of the Npc1nmf164 mutation from the C57BL/6J inbred strain to the BALB/cJ inbred strain increased the mean lifespan from 117.8 days to 153.1 days, confirming that the severity of the NPC1 phenotype is strongly influenced by genetic background. The transfer of another Npc1 allele, Npc1nih, to this background also extended survival of the homozygotes indicating that the modifying effect of BALB/cJ is not limited to a single allele of Npc1. The increased longevity due to the BALB/cJ background did not map to a previously mapped modifier on chromosome 19, indicating the presence of additional genes impacting disease severity. The previously studied Glial Fibrillary Acidic Protein promoter-Npc1 cDNA transgene (GFAP-Npc1) which only expresses NPC1 in astrocytes further extended the lifespan of Npc1nmf164 homozygotes on a BALB/cJ background (up to 600 days). Hydroxypropyl-β-cyclodextrin (HPβCD) treatment, not previously tested in the Npc1nmf164 mutant, extended life in the Npc1nmf164 homozygotes but not the transgenic, Npc1nmf164 mice on the BALB/cJ background. In all cases, lack of weight gain and early cerebellar symptoms of loss of motor control were found. At termination, the one mouse sacrificed for histological studies showed severe, diffuse pulmonary alveolar proteinosis suggesting that pulmonary abnormalities in NPC1 mouse models are not unique to the Npc1nih allele.