Fine Mapping of an Amyotrophic Lateral Sclerosis Modifier Locus to a Single BAC

Mutations in the Cu/Zn superoxide dismutase (SOD1) gene are responsible for 15-20% of familial amyotrophic lateral sclerosis (FALS) cases. Severity of the ALS phenotype is dependent on genetic background for mice carrying the mG86R SOD1 transgene. A BAC (149m19) containing several candidate genes (Serf, Smn, Naip2 and Naip5) and derived from 129Sv genomic DNA was used to investigate whether these genes partially rescue the mG86R SOD1 (FVB/NJ) ALS phenotype by delaying ALS onset. Two single-insertion BAC lines were produced and both mRNA and protein for BAC genes were shown to be elevated. Mice heterozygous for mG86R SOD1 and BAC149m19 in the FVB/NJ background were shown to have significantly delayed ALS onset compared to mG86R SOD1 controls. BAC 149m19 did not significantly delay ALS onset for mice carrying the human G93A SOD1 mutation in the FVB/NJ background. Delayed ALS onset for BAC/mG86R mice was not due to reduced SOD1 expression. Overexpression of one or more of the BAC genes appears to be linked to the severity of ALS phenotype in mice, but in a mutation specific manner.