White Shepherd is originally German Shepherd Dog having white coloured coat. First German Shepherd Dogs grandfather was a white dog Greif. It was not until the 1930's. after the death of Max von Stephanitz, that white dogs were discriminated against. The discrimination increased with the rise of Hitler. Whites puppies born were killed and not registrated into studbook and White German Shepherd disappeared from Europe. For saving the White Shepherd we must thank the Americans and Canadians that kept breeding and fighting for the White Shepherds. White Shepherds were brought back into Europe in late 70's and then the breed was known as White German Shepherd, American-Canadian White Shepherd or just White Shepherd.
The White Shepherd has not been mixed with any other breed of dog. Certainly, there has been no other breed or breeds added in order to make them white. The gene that controls the white color is a natural component in the total color genetic makeup of the German Shepherd Dog breed. In America the White Shepherd is registered independently with the American White Shepherd Association in the United States of America. In Europe the breed is today recognized by FCI and known as White Swiss Shepherd.
White Shepherd History in America can be found at the AWSA web page
Article about White Shepherd history
A good article about White Shepherd by Fred Lanting