Compositions and methods for inhibiting expression of a mutant gene

A pharmaceutical composition for selectively inhibiting the expression of a mutant target gene in a mammal, the composition comprising:

• a dsRNA and pharmaceutically acceptable carrier, wherein the dsRNA comprises:
• a first strand that has a complementary region that is complementary to at least a portion of an RNA transcript of at least part of the mutant target gene;
• and
• a second strand of the dsRNA, wherein the first and second strands are complementary or substantially complementary to each other,
• wherein the first and second strands of the dsRNA are 19 to less than 30 nucleotides in length,
• wherein the complementary region of the first strand of the dsRNA contains a mismatch relative to the mutant target gene and at least one more mismatch relative to a wild type form of the mutant target gene, and
• wherein the dsRNA selectively inhibits expression of the mutant target gene in a mammalian cell relative to the wild-type form of the mutant target gene.