The present invention relates to a double-stranded ribonucleic acid (dsRNA) for inhibiting the expression of a mutant gene, comprising a complementary RNA strand having a complementary region that is substantially complementary to a portion of the mutant gene, and which is partially complementary to the corresponding wild-type gene. The invention further relates to a pharmaceutical composition comprising the dsRNA and a pharmaceutically acceptable carrier. The pharmaceutical compositions are useful for inhibiting the expression of a target mutant gene, as well as for treating diseases caused by expression of the target gene. The invention also relates to methods for inhibiting the expression of a target mutant gene, as well as methods for treating diseases caused by the expression of the target gene.