If the disease is uncommon, as with the progressive rod - cone degeneration (PRCD) form
of Progressive Retinal Atrophy in Australian Shepherds, or if use
of a test and careful breeding decisions have markedly reduced the frequency
of a formerly common mutation (think what could be done with CEA in Collies,) testing could then be
confined to only those
dogs with known family
history of the disease or with relatives that have been DNA tested as carriers.