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Updated Report on PRA in Tibetan Spaniels - Maureen Sharp October 2004


We feel it is time to bring everyone up to date with the PRA project. As you know the AHT have continued to work on our project and have got so far but desperately need blood from a few more PRA cases with their close relatives to check their findings (possible 2-3 families just might be enough).

To recap blood has been collected from over 294 Tibetan Spaniels, of which 19 are affected with PRA. DNA has been extracted from each blood sample and the AHT have focused on a Homozygosity Mapping approach to find markers linked to the PRA gene. They have analysed 340 markers with 6 affected dogs and 10 carriers and identified markers, which are homozygous for the same allele in at least 4 affected dogs and heterozygous in at least two carriers. Twenty markers meet the above criteria, these are located on 16 different chromosomes. Four canine chromosomes have two markers each that meet the criteria so they have focused their efforts on those. They identified 8 additional markers from these four promising chromosomes and have typed these markers on all the Tibetan Spaniels samples. Unfortunately the results are inconclusive due to the limited number of families available, meaning that to date they are not able to either confirm or exclude any of these four chromosomes.

Until more blood samples are forthcoming the AHT have been looking at the available canine whole genome sequence to isolate genetic markers located in genes that are known to cause retinal disease in humans. They are examining them in the Tibetan Spaniel pedigree for evidence of linkage, in the hope that if one of them is the gene responsible for PRA it will be so tightly linked to the disease within the pedigree they will be able to detect the linkage. They are also making efforts to contact other researchers working on PRA in Lhasa Apsos, in an attempt to pool the results. The conditions are very similar between the two breeds so it is possible the same gene is responsible for the two conditions. They also continue to collect and store blood samples from affected dogs and their close relatives.

Early this year an Italian vet joined the AHT for a few months and worked very hard finding genetic markers next to genes that are known to cause PRA in other breeds, or similar diseases in humans, and analsying them in the Tibetan Spaniels samples for evidence of linkage to PRA. She found a genetic marker near to one particular gene that gave us the highest lod score we have ever seen with the Tibetan Spaniels and although this is encouraging we must wait developments as it is possible it could be a false positive result. This particular chromosome has quite a few PRA genes on it, so they are in the process of looking further into this.

We understand that there is a new case of PRA in Sweden and although we have been unsuccessful in getting blood from Tibetan Spaniels there we are hopeful that they, in view of the above will help. We send our sympathies to the breeders and owners concerned but hope that the urgent need for new blood from PRA families and the fact that we may be very near to a DNA test will encourage them.

We started this project in May 2000 and I think that congratulations are in order to the whole breed for what we have achieved.

Maureen Sharp (Co-ordinator - PRA Fund) is home of the PRA Fund and the South East & East Anglian Tibetan Spaniel Society