The invention provides for a method for selectively reducing the expression of a mutant mRNA and/or protein having an expanded nucleotide repeat relative to a wild-type mRNA, comprising contacting a cell with an antisense oligonucleotide of sufficient length and complementarity to the expanded nucleotide repeat. More particularly it relates to selectively reducing the expression of mutant Huntington protein associated with Huntington's disease. The antisense oligonucleotide comprising either a nucleotide or a repeated three nucleotide sequence as defined in the claims.