The present invention provides a method of modulating the expression of a gene containing expanded nucleotide repeats in a cell, comprising: inhibiting the biological activity of SPT4 or SUPT4H; and regulating the formation of R-loops. The inhibition step can effectively reduce the expression of the gene containing the expanded nucleotide repeats and the regulatory step can further enhance the inhibition step. The inhibition step and the regulation step are for the purpose of regulating gene expression by interfering the capacity of RNA polymerase II transcribing over a DNA template with lengthy nucleotide repeats.