Day Blindness in WHD: AHT Research Screening Results
Following our request to the AHT to carry out a research screening programme for a form of PRA in Wirehaired Dachshunds, we have now received their report and analysis...
In 2008, researchers in Norway, Sweden and the USA identified the mutation responsible for an early-onset form of cone-rod dystrophy (CRD) in Standard Wire-Haired Dachshunds (SWHDs). This mutation occurs in a gene known as nephroretinin (NPHP4) and is responsible for a "day blindness" form of progressive retinal atrophy (PRA). Geneticists working in the Kennel Club Genetics Centre (KCGC) at the Animal Health Trust (AHT) subsequently found that this mutation is also present at a low frequency in the UK population of Miniature Wire-Haired Dachshunds. The AHT has since made a DNA test available to both wire-haired varieties.
To investigate these findings further, the KCGC was asked by the Wire-Haired Dachshund Club to determine the frequency of the NPHP4 mutation in UK SWHDs. To this end DNA was collected from a set of 39 SWHDs (20 dogs, 19 bitches) all of whom were registered with the UK Kennel Club. All 39 dogs, who ranged in age from 6 months to 13 years and who each had a unique sire and dam within the sample cohort, were DNA tested for the NPHP4 mutation.
Of the 39 dogs screened for the mutation, a single dog was found to be a carrier (one copy of the mutant allele) and the remaining 38 dogs tested clear (no copies of the mutant allele). Since each dog possesses two copies of the NPHP4 gene, the frequency of the mutation can be calculated as one in 78, which is equal to 0.013 (1.3 %).
Assuming that the dogs that were sampled represent a random subset of the UK population and that mating between dogs occurs randomly with respect to this mutation, the Hardy-Weinberg equilibrium equation can be applied. If p represents the normal allele and q represents the mutant allele, the equation p2 + 2pq + q2 = 1 is used to calculate the percentage of clear, carrier and affected dogs in the population. Using this approximation, we therefore estimate that 97.4% of SWHDs in the UK are clear of the mutation, 2.57% are carriers and 0.017% are affected.
We are grateful to Christine Gibson of the WHDC for coordinating this programme.
We have discussed these results with Dr. Cathryn Mellersh at the AHT in order to make recommendations to owners of SWHDs. The frequency of this mutation in the breed is very low, but it is known to be associated with dogs of Scandinavian breeding.
It is therefore recommended that anyone whose dogs have Scandinavian ancestors, or anyone planning such a mating, SHOULD make use of this NPHP4 DNA test. Any Carrier or Affected dogs should only be mated to Clear dogs.
On the basis of this research, there is no evidence that dogs of pure US or UK breeding carry this mutation.