Although further studies are needed to identify causal genes in respective Mts-QTLs, the panel of candidate genes with reported gene expression changes or polymorphisms in breast cancer patients, Prlh for Mts-1, Anpep or Blm for Mts-2, Ece1 for Mts-3, and Smad2 for Mts-4_validate the hypotheses that these genes should be studied further in different experimental systems and in humans as potential susceptibility genes for mammary tumorigenesis. The gene discussed is PRLH; the disease is breast cancer.