XL-PRA is a "late-onset" form of PRA, first clinical signs at 3-5 years. May be detectable by an ophthalmologist as early as 5 months. Signs include loss of night vision followed some time later by loss of day vision leading to blindness. Owners report dog's eyes seem to have more "shine" and the dog develops "tunnel vision" and dilated pupils. The X-linked inheritance means the risks of developing the disease effect males and females differently. Females who inherit the defective gene from one parent and a normal gene from another parent (carriers) won't be affected, but may have subtle defects that don't normally impact vision. Male pups who inherit the defective gene from the dams will be effected (there aren't male "carriers") Special breeding advice should be sought, if you are unfamiliar with X-link disease inheritance.