Test Detail

Collie eye anomaly (CEA, choroidal hypoplasia due to NHEJ1)

Ocular · Dog

Collie eye anomaly (CEA) is an inherited disorder of ocular development that mainly affects herding breeds with Collie ancestry (Rough and Smooth Collie, Border Collie, Shetland Sheepdog, Australian Shepherd). It is associated with a deletion in the NHEJ1 gene on chromosome 37 (risk allele linked to the locus in several herding breeds) and causes abnormal development of the inner layers of the eye, with choroidal hypoplasia as the main finding. Severity is highly variable, from subclinical cases to blindness, even between littermates, which suggests modifier genes.

Inheritance pattern	Autosomal recessive (OMIA:000218-9615). Homozygotes for the risk allele show the anomaly to a variable degree; heterozygotes are carriers.
Gene / Mutation	NHEJ1 (chromosome 37, CFA37): 7.8 kb intronic deletion (7:g.28697542-28705340del7799) spanning a conserved protein-binding domain. It behaves as a risk allele linked to the CEA locus in several herding breeds; OMIA classifies it as a locus-linked marker, not as a causal mutation confirmed in all breeds.
Penetrance	Variable expression, even between homozygous littermates; severity is modulated by modifier genes. Penetrance and the exact causal relationship may differ between breeds, so complete clinical equivalence should not be assumed.
Code	vcui
Turnaround time	7 days
Price	32,58 €

Incidence

Described in Rough and Smooth Collie, Border Collie, Shetland Sheepdog and Australian Shepherd. The specific frequencies of affected/carrier animals per breed are not firmly established in the verified sources; prevalence has decreased where systematic genetic screening is carried out.

Breeder management

- Test the entire breeding line before the first mating (NHEJ1 test)
- Do not mate two carriers (25% of homozygotes)
- Affected animals (homozygotes) should not be bred
- Carriers should only be mated to non-carriers
- Carry out ophthalmological screening at 6-8 weeks (window before pigmentation)
- Periodic ophthalmological examination by a certified ophthalmologist
- Keep records of the genetic test in the pedigree
- The 'go normal' phenomenon (hypoplasia that becomes pigmented and is no longer visible) does NOT mean that the dog is healthy or that it does not transmit the disease

Specialist notes

The severity of CEA cannot be predicted from the genotype alone: one homozygote may have mild signs while a homozygous littermate is severely affected. The ophthalmological examination at 6-8 weeks is crucial because afterwards pigmentation can mask the choroidal hypoplasia ('go normal' phenomenon). There is no treatment that corrects the structural anomaly; management focuses on environmental adaptations and, in selected cases with retinal detachment, preventive laser surgery if detected early.

References

1. Lowe JK, Kukekova AV, Kirkness EF, et al. Linkage mapping of the primary disease locus for collie eye anomaly. Genomics. 2003;82(1):86-95. PMID: 12809679
2. Parker HG, Kukekova AV, Akey DT, et al. Breed relationships facilitate fine-mapping studies: a 7.8-kb deletion cosegregates with Collie eye anomaly across multiple dog breeds. Genome Res. 2007;17(11):1562-1571. PMID: 17916641

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