And remember that a portion of the sampled population was referred from local practitioners, who evidently had some suspicion of a problem. The true incidence rate and carrier rate may be somewhat smaller. The presence of PRA in the USA is not surprising. The numbers from English sources are growing steadily. And this, too, is understandable.
Genetic problems tend to accumulate in isolated populations such as in a quarantine country.
Furthermore, North American sources can be used for breeding with a certain amount of confidence. Importation from North American sources can help breeders in Europe rejuvenate their gene pool, and breed their way out of their present predicament. Denmark has the same bloodlines, but as yet has released no results. If you knew you had a 540 times greater than normal chance to go blind if you ate spinach, I am sure you would never touch it again, the bottom would drop out of the spinach market, and the Government would probably pass a law against it. But this is only relative.