Post date: Oct 28, 2011 2:37:28 PM
We have received the following update from Centogene who are conducting the current Lafora Screening tests for MWHDs...
Centogene would like to provide an update on the Lafora disease screening and research programme to the Wirehaired Dachshund Club. Centogene is a human genetic disease testing laboratory in Rostock, Germany, focussing on genetic testing of rare inborn human diseases. Centogene has been selected by the club to apply a test for the screening of MWHD samples which is able to differentiate between “clear” animals, carriers of Lafora´s disease and animals which will develop Lafora´s disease later in their life or to confirm a diagnosis based on disease symptoms. In addition, it has been agreed to further investigate the genetic background of Lafora´s disease in MWHD.
Lafora´s disease is, in humans and dogs, a form of epilepsy. The difference is that there are mutations which cause Lafora´s disease in humans which have not been found in dogs. The genetic background of Lafora´s disease in MWHD has been investigated by a group of researchers at the Hospital for Sick Children in Toronto, Canada. This ground-breaking work is still based on the investigation of a low number of dogs and it remains to be seen if the investigation of a larger number of MWHD might result in the finding that additional genetic alterations contribute to Lafora´s disease. From a genetic point of view Lafora´s disease in dogs resembles Corea Huntington disease in humans.
In dogs, Lafora´s disease is caused by the expansion of a part of the EPM2 gene. Expansion of the gene prevents at the end the biosynthesis of a protein. Lack of the protein causes Lafora´s disease.
Centogene initially performed tests with samples of Dachshunds with known disease status. These tests indicated that the test was suitable for a screening to differentiate between clear, carriers and affected dogs. The subsequent testing of 96 samples revealed that the differentiation between clear and carriers is impaired by individual genetic differences of the investigated dog samples.
Centogene´s testing results have demonstrated that differences in the length of the expansion have a strong impact on the ability to detect carriers of Lafora´s disease in dogs. A short expansion can be detected by Centogene´s test while larger expansions cannot be detected. The expansion results in a structure which prevents the biosynthesis of a protein, but also impairs the application of standard testing methods.
The test can be used to detect dogs which will develop Lafora´s disease but is currently not suitable to detect the majority of carriers. Within 96 tested samples 10 affected dogs have been identified. Some of these dogs either suffer already from Lafora´s disease and/or had been identified as affected by the Canadian test. Specific detection methods applied by Centogene have proven that expanded versions of the EPM2 are being detected.
In 2010 the Canadians identified 12 affected dogs from 95 samples. Centogene has now tested a large cohort of MWHDs and identified a similar proportion of affected dogs. We would like to emphasise that this is still a very low proportion of the total population of MWHDs, but it indicates that Lafora´s disease is more frequent, as reported by the Canadian group in 2005. This implies that the number of carriers is also higher, as previously expected. I will come back to this issue at the end of my report.
Affected dogs will always transmit expanded EPM2 genes to their offspring. Dependant on the genetic status of the other mating dog the offspring will be at least disease carriers or affected dogs. Identifying affected dogs has potentially the largest impact on reducing the frequency of Lafora´s disease. Nevertheless, additional methods will be applied by Centogene to detect carriers of Lafora´s disease with larger expansions of the EPM2 gene. Within the last month more sensitive detection methods have been tested to prove if longer versions of the expanded EPM2 gene can be detected in samples of carriers. The results indicate that earlier steps in the testing procedure still need to be modified.
We suggest continuing the programme in the following way. Owners of dogs which have been tested as affected will be informed of the result. We suggest not breeding from those dogs. In cases where the differentiation between clear and carrier needs the application of additional testing methods, no intermediate result will be sent out and Centogene will apply these methods. In the vast majority of samples received by Centogene the amount and quality of the DNA is sufficient for further testing. In case additional samples are required Centogene would inform Mrs. Nora Price (Lafora Coordinator for the WHDC).
We apologize for the inconvenience. The worldwide experience in genetic testing of Lafora´s disease is still extremely limited and the results of the Canadian group in 2005 demonstrated that the particular genetic mechanism which causes Lafora´s disease in dogs poses a major challenge to the identification of Lafora´s disease carriers in MWHDs. Since that discovery of the genetic background of Lafora´s disease in dogs, genetic testing methods have made significant progress. Centogene is using a different approach compared to the Canadian group. The first results indicated that this would work for the identification of carriers. The positive control makes us confident that further refinement of the test established by Centogene will be the basis for robust carrier identification.
Within the next 4 weeks Centogene is introducing different modifications of the test. Samples from dogs with known disease status will be used for the validation. At latest, at the end of November Centogene and the Wirehaired Dachshund Club will review the results and decide on how to move on with the programme. As indicated above, the current results point in the direction of up to 10% affected dogs. From a statistical point of view this means about 20% carriers would be expected in the sample population. These numbers need to be confirmed in larger cohorts and it is likely that carriers need not be excluded from breeding, providing they are only mated to clear dogs. Reducing the so-called gene pool (number of dogs participating in breeding programs) will have potentially detrimental effects on other inborn diseases. It would have a benefit on Lafora´s disease maybe at the expense of increasing the number of dogs suffering from other genetic diseases.
We ask you for your understanding that we are dealing with a difficult disease and that recommendations on breeding strategies need to take the disease frequency in account.
Costs for the refinement of Centogene´s test as indicated above are carried by Centogene and are not at the expense of the Wirehaired Dachshund Club.
Dr. Stefan Maeser
October 20th 2011