Genetic Testing for CEA: Labs, Costs, Interpretation

The identification of the NHEJ1 gene mutation responsible for Collie Eye Anomaly in 2007 transformed our approach to this condition. For the first time, breeders could determine a dog's genetic status with certainty, regardless of clinical appearance. Having been involved in validating testing protocols and advising breed clubs on their implementation, I have observed how genetic testing has become an indispensable tool for conscientious breeders. Yet questions remain about which tests to use, how to interpret results, and how DNA testing relates to the clinical examination I discussed in my previous article.

The Science Behind the Test

Collie Eye Anomaly results from a 7.8 kilobase deletion in the NHEJ1 gene located on canine chromosome 37. The NHEJ1 gene encodes a protein involved in DNA repair mechanisms, though its precise role in eye development is still being elucidated. What matters practically is that this mutation is remarkably consistent across affected breeds; the same deletion causes CEA in Rough Collies, Shetland Sheepdogs, Border Collies, Australian Shepherds, and other affected breeds.

The inheritance follows a simple autosomal recessive pattern. A dog must inherit two copies of the mutant allele (one from each parent) to be affected. Dogs with one normal and one mutant copy are carriers who appear clinically normal (or may have very subtle findings) but can pass the mutation to offspring. Dogs with two normal copies are genetically clear.

Modern genetic tests for CEA typically use polymerase chain reaction (PCR) techniques to detect the presence or absence of the deletion. The test is highly accurate when performed by reputable laboratories, with sensitivity and specificity approaching 100% for detecting the mutation itself.

Available Testing Laboratories

Several laboratories worldwide offer CEA/NHEJ1 testing. I have worked with many of these facilities over the years and can offer observations on their services. Costs quoted are approximate and subject to change.

Interpreting Your Dog's Results

Test results are reported using various nomenclatures, which can confuse owners accustomed to one system when presented with results from another laboratory. Let me clarify the common formats.

The Critical Distinction: Genotype vs. Phenotype

One of the most important concepts I emphasise to breeders is that genetic testing tells you what genes a dog carries, not how severely those genes are expressed. Two dogs with identical "affected" genetic results may have profoundly different clinical presentations; one might have barely visible choroidal hypoplasia whilst another has vision-threatening colobomas.

This is why genetic testing complements but does not replace clinical examination. The genetic test tells you:

• Whether the dog can produce affected puppies
• The genetic status to record for breeding planning
• Whether a clinically normal-appearing adult might be a "go normal" affected dog

The clinical examination tells you:

• The actual structural changes present in the eyes
• The severity grade and location of lesions
• The prognosis for vision
• Whether complications like colobomas or detachment are present

Neither test alone provides complete information. I recommend both for any dog being considered for breeding.

Testing Strategy for Breeders

How should breeders incorporate genetic testing into their programmes? My recommendations depend on your starting point and goals.

Establishing Baseline Status

If you are new to breeding or have never tested your dogs, begin by testing all current breeding stock. This establishes your baseline and allows informed mating decisions going forward. The initial investment pays dividends through every subsequent generation.

Testing Puppies

I advise testing puppies before sale, particularly those intended for breeding. Buyers increasingly expect DNA test results, and providing them demonstrates commitment to transparency. Many breeders now include testing costs in puppy pricing.

For pet homes where breeding is not intended, DNA testing is optional but can provide peace of mind. Owners of affected dogs benefit from knowing their status for veterinary care planning.

Integrating with Clinical Examination

My standard protocol for breeding dogs combines examination at 6-8 weeks with DNA sample collection at the same visit. Results return before puppies leave for new homes. For adult dogs being introduced to a breeding programme, both examination and genetic testing should be completed before the first mating.

Common Questions About Testing

Can I Test With a Home Cheek Swab Kit?

Yes, most laboratories provide mail-in swab kits. The procedure is simple: rub the provided brush firmly against the inside of your dog's cheek for 15-30 seconds, allow it to dry, and return it in the provided envelope. Avoid collecting samples immediately after eating. Proper technique ensures adequate DNA for testing.

Are Results from Different Labs Comparable?

All reputable laboratories test for the same NHEJ1 deletion, so results should be consistent. Occasionally, nomenclature differences cause confusion (one lab's "carrier" is another's "+/-"), but the underlying genetic determination is the same. If results seem inconsistent, contact the laboratories for clarification.

Do I Need to Retest if My Dog Has Been Tested Before?

Genetic status does not change over a dog's lifetime. A test performed as a puppy remains valid forever. However, registration bodies may require tests from approved laboratories, so verify acceptance before relying on historic results for official purposes.

My Dog Tested Affected but the Eyes Look Normal. Is the Test Wrong?

Almost certainly not. This is the "go normal" phenomenon; increased retinal pigmentation with age can mask underlying choroidal hypoplasia that was visible in early puppyhood. The genetic test correctly identifies the genotype. This underscores why puppy examinations should occur at 6-8 weeks and why breeding decisions should incorporate genetic test results, not just clinical appearance.

Limitations of Current Testing

While CEA genetic testing is highly accurate for detecting the NHEJ1 mutation, several limitations merit acknowledgment.

First, the test identifies carriers and affected dogs but cannot predict clinical severity. As I discussed in my article on understanding CEA severity, modifier genes influence whether an affected dog has mild choroidal hypoplasia or severe colobomas. These modifiers are not yet characterised for commercial testing.

Second, the test assumes CEA in your breed results from the known NHEJ1 mutation. Whilst this is true for the vast majority of cases, theoretical possibility exists that other mutations could cause similar phenotypes. I have not encountered such cases in practice, but diagnostic humility is appropriate.

Third, testing requires accurate identification of the sample source. If samples are mislabeled or swapped, results will not reflect the intended dog. Laboratories implement quality controls, but owners and breeders must also maintain careful sample handling.

The Future of CEA Testing

Research continues into the modifier genes that influence CEA severity. My collaborators at Cornell and Edinburgh are working to identify variants associated with coloboma development. Should these be characterised, future tests might predict not just affected status but likely severity, further refining breeding decisions.

Additionally, genome-wide panels are becoming increasingly comprehensive and affordable. Within a few years, I anticipate standard panels will include CEA alongside dozens of other health markers, providing unprecedented insight into inherited disease risk with a single test.

For now, combining expert clinical examination with NHEJ1 genetic testing provides the information breeders and owners need to make sound decisions. The modest investment in testing yields lifelong certainty about genetic status and guides integrated health screening programmes that benefit dogs across generations.