CEA is inherited in an autosomal recessive fashion with variable expressivity meaning that dogs must inherit two copies of the associated NHEJ1 gene mutation (one from each parent) in order to develop the disease. However, “variable expressivity” means that the severity of CEA in affected dogs may vary significantly from dog to dog. Therefore, mildly affected parents can produce severely affected puppies and vice versa. On top of that, dogs that only inherit one copy of the associated mutation do not show clinical signs of CEA, but are considered carriers of the disease and can have CEA affected puppies if bred to another CEA carrier or affected dog. Therefore, genetic testing of dams and sires is absolutely critical for eliminating this disease from a blood line. In order to avoid producing affected puppies, all carriers of the NHEJ1 mutation should be bred to dogs that have not inherited the mutation. This pairing will not result in any affected dogs, but it should be noted that about 50% of the litter would still be carriers of the mutation. As with any inherited disease, it is not recommended to breed affected dogs; this is true even if the dog you’d like to breed has “gone normal” due to the aforementioned inability to predict disease severity.