Disclosed herein are compositions and methods for reducing expression of C90RF72 mRNA and protein in an animal. In particular, the invention relates to a modified antisense oligonucleotide against C90RF72, which has the nucleobases sequence of 5’-GCCCCTAGCGCGCGACTC-3’ and comprises a particular pattern of modification of the internucleoside linkages. Such nucleotide and methods are useful to treat, prevent, ameliorate, or slow progression of neurodegenerative diseases in an individual in need thereof.