The present invention provides a composition for suppressing the expression of the CKAP5 gene, the composition comprising a lipid particle containing a double-stranded nucleic acid as a drug and a cationic lipid,the double-stranded nucleic acid having an antisense strand having a base sequence complementary to the sequence of at least 19 continuous bases in CKAP5 gene mRNA of any one of SEQ ID NOs: 1 to 6,the cationic lipid being represented by formula (I):whereinR1 and R2 are the same or different and are each linear or branched alkyl, alkenyl or alkynyl of 12 to 24 carbon atomsL1 and L2 are the same or different and are each —CO—O— or —O—CO—a and b are the same or different and are each 1 to 3 andR3 is a hydrogen atom, alkyl of 1 to 6 carbon atoms, or alkenyl of 3 to 6 carbon atomsa medicament comprising the composition, and the like.
