In a very few breeds, such as the American Staffordshire Terrier, Old English Sheepdog, Brittany Spaniel, and Gordon Setter, symptoms do not appear until adulthood or even middle age.

• 极少数犬种，如美国斯塔福梗、古代英国牧羊犬、不列塔尼猎犬和戈登雪达犬，直到成年甚至中年才有症状表现。