The present invention provides a single-stranded antisense
oligonucleotide or pharmaceutically acceptable salt thereof for regulating the expression and / or function of the ATXN7
gene. In the single-stranded antisense
oligonucleotide, each
nucleotide is bonded by a
phosphate group and / or modified
phosphate group. The single-stranded antisense
oligonucleotide includes a gap region, a 3' wing region bonded to the 3' terminal of the gap region, and a 5' wing region bonded to the 5' terminal of the gap region. The gap region is a
deoxyribose-constituted
nucleic acid in which a
nucleic acid modified by a
sugar moiety may be included. The 3' wing region and the 5' wing region are modified nucleic acids. The
sugar modification constituting the single-stranded antisense oligonucleotide is a modified
nucleic acid represented by formula (A1). The single-stranded antisense oligonucleotide has a base length of 12-30 mer. The
base sequence of the antisense oligonucleotide is: a
base sequence having a
sequence identity of 90-100% with a
base sequence that is complementary to at least one target region constituted at the same base length as the antisense oligonucleotide in the base sequence shown in SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, or SEQ ID NO: 5; a base sequence that is complementary to the base sequence obtained by deleting, substituting, inserting, or adding one or more bases in the target region; or a base sequence that, under stringent conditions, hybridizes with an oligonucleotide having the target region.