The Golden Retriever Club

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Progress report for the study of MRD, HC and PRA in the Golden Retriever at the Animal Health Trust

 

Sample Collection.

The collection of blood samples from Golden Retrievers (GRs) affected with Multifocal retinal dysplasia (MRD), hereditary cataract (HC) and progressive retinal atrophy (PRA) and their close relatives is on going. To date we have collected samples from 267 golden retrievers. The numbers of dogs affected with each disease that can usefully contribute to each study is shown below:
MRD (18)
HC (18)
PRA (11)

DNA has been extracted from each blood sample and is currently being stored at -20°C.

 

 

 

Initial Experiments to Determine Genetic Heterogeneity of GR Population

We have carried out initial experiments to genotype a small number of genetic markers on a subset of the GRs we have collected, to determine the genetic heterogeneity of the GR population. The number of alleles observed in the population is taken into account in calculating the number of samples it is necessary to collect to be confident of obtaining a statistically significant linkage result from a genome scan.

Our experiments indicate the average number of alleles per marker segregating in the GR population is 3.1.

 

 

 

Computer Simulations to Determine Statistical Power of GR Collection to Detect Linkage

To maximise both time and cost efficiency we do not commence any genome scan until sufficient samples have been collected for us to be confident of obtaining a statistically significant linkage result. Therefore we regularly monitor the power of the collection of GR samples to detect markers genetically linked to each disease we propose to study. We simulate 1000 sets of genotyping data for markers segregating both three and four alleles, located at different distances from the disease gene. The results give us an idea of how likely we would be to obtain significant results in a real genome scan. The results from the most recent simulations indicate that for MRD we have collected sufficient samples to commence a genome scan, and for HC we are very close to having enough samples. We anticipate the addition of two or three more affected individuals to our current collection will be sufficient for us to be confident of obtaining a significant result from a genome scan, providing samples could also be collected from parents of the affected dogs and at least one sibling each. For PRA we currently do not have sufficient samples commence a genome scan.

 

 

Current Activity

 

Additional samples need to be collected from dogs affected with PRA and HC and their close relatives. We continue to extract and store DNA from blood samples that are sent to us and to monitor the power of the samples to detect linkage. We will also continue to collect and store MRD samples; the more samples we have the more quickly we will be able to confirm any linkage results suggested by the genome scan.
We have started the genome scans for MRD and HC. Although we still need a small number of additiona HC samples to be confident of obtaining a significant linkage result (see above) we do currently have sufficient samples to obtain a 'suggective' linkage reuslt, and in the interests of time and efficiency we decided to commence both the MRD and HC genome scans simultaneously. We have typed 100 markers with each collection and have analysed the data from 60 of the markers with the HC dogs. To date none of the markers show any evidence of being linked to HC, but with this relatively small number of markers that result is not unexpected.

 

 

Future Activity

We will continue to analyse the data we have collected over the next month or so. For any markers that show evidence of linkage to either MRD or HC we will identify additional genetic markers on the same chromosome(s) and type those on the pedigree(s) in an attempt to confirm initial putative linkages. If none of the initial 100 markers show any evidence of linkage to either HC or MRD we will analyse additional markers on the pedigrees.
We arrange the genetic markers into groups (called multiplex groups) that can be analsyed together in a single experiment. This strategy saves considerable amounts of time and money. We are at present, in collaboration with a laboratory in the United States, working to arrange a set of approximately 350 markers into multiplex groups. This work is substantial but we are making good process and are hopeful that these new multiplexes will be ready to use by the end of the year.