Furthermore, Ireland has world frequency extremes (or near extremes) for many variants that are suspected of having undergone selection, including disease-related genes, for example: the cystic fibrosis locus, CFTR [3,4]; the ABO blood group and the rhesus blood factor [5]; GALT, associated with galactosemia [6]; HFE, associated with haemochromatosis [7]; and PKU, associated with phenyketonuria [8]. This evidence concerns the gene CFTR and cystic fibrosis.