One special medical problem comes in the Scottish Fold if both parents have folded ears. In such a case, their kittens will be very likely (1:4 ratio, or usually at least one per litter) to have a painful joint disease that can fuse the tail, ankles and/or knees. Scientists think the disease is caused by the dominant (folded-ear) gene. It is more likely to affect Folds with the gene twice, than mixed single with one recessive (unfolded-ear) gene. This disease can also affect Scottish Folds with one copy of the gene, but usually not as often or as badly. For this reason the breed is not accepted by either the Governing Council of the Cat Fancy or the Fédération Internationale Féline. This is the reasoning behind the widely-held belief that the only ethical manner of breeding Folds is Fold/nonfold and not Fold/Fold (in the same way Munchkins are bred).