To decipher the molecular events that lead to the increased tumourigenesis associated with polyQ-huntingtin expression, we examined the gene expression patterns of MMTV-PyVT/HdhQ7/Q7 and MMTV-PyVT/HdhQ111/Q111 mammary tumours using Affymetrix Mouse Exon 1.0 ST microarrays (Fig 2). The gene discussed is HTT; the disease is breast cancer.