cord1 PRA test update

Laboklin UK have recently announced that they will no longer be offering the cord1 PRA test, other than for research purposes. They refer to a study which was published on 17^th July 2012 by the Association for Research in Vision and Ophthalmology.

We have consulted with the Kennel Club and Animal Health Trust to seek clarification of the findings in this paper and their response is in the attached document.

In brief: the new paper adds nothing to what we have known since 2009, that there's a second, modifying, mutation that needs to be present for early onset PRA in cord1 Affected dogs and that, without this, PRA is more likely to be late onset. Additionally, we know from AHT research that ERG testing shows that cord1 Affected dogs do indeed have reduced retinal function. So, the recommendation continues to be that there is value in doing the cord1 test and that Affected and carrier dogs should only be mated to Clear dogs. The Breed Council also recommends that clinical eye examinations should also be used by breeders to help ensure only dogs with healthy eyes are bred from.

Dr. Cathryn Mellersh (AHT), together with Dr. David Sargan (Cambridge University), summarise the situation as follows:

Data presented in the recent paper from the Aguirre lab are consistent with many previously published observations from other research teams and the following points summarise our current understanding of cone-rod dysplasia in miniature longhaired dachshunds;

• • dogs that are homozygous for the RPGRIP1 mutation (ins/ins) will not necessarily develop retinal degeneration (RD) at an early age, although some will.

  • Ins/ins dogs usually have abnormal or absent cone photoreceptor function although the degree of loss depends on age of testing and is later in some dogs than others. They may also have abnormal retinal histopathology.

  • There is an additional mutation, in a second gene, that influences the age of onset of retinal degeneration and homozygosity at both the RPGRIP1 locus and the newly mapped second region is necessary for a dog to develop early-onset RD.

  • The involvement of the RPGRIP1 locus is definitive, based on the perfect association with cord1 in the AHT research colony, although we now know an additional mutation is involved, in a second region of the genome, that determines the age of onset of RD.

Read the full document here.

We are grateful to Cathryn Mellersh for her permission to publish this document.