Submitted to the Foundation of the Cairn Terrier Club of America, August 26, 2003
Patrick J. Venta, Ph.D.
Small Animal Clinical Sciences
College of Veterinary Medicine
Michigan State University
East Lansing, MI 48824-1314
We are continuing our search for the CMO gene through two approaches. The first is by testing particular candidate genes as being causative for CMO. The second is by a whole genome scan approach. With the first approach, we started by testing the hypothesis that a gene involved in human Paget?s disease, speculated to be the human equivalent of CMO in the scientific literature, was in fact the causative gene. At the time that we started the CMO project the identify of this gene had not been made, although it was known to be located in a particular part of human chromosome number 18 (humans have 23 pairs of chromosomes that are numbered according to size; dogs have 39 pairs of chromosomes, also numbered according to size). Although we tentatively excluded this gene as being at the basis of CMO based upon the limited known comparative information about the two genomes, we wanted to be more certain about this exclusion. The human gene was eventually identified but for technical reasons it could not be directly studied in the dog. However, we used an approach developed in our lab to produce a much better map of the canine genome region surrounding this gene, identified a tightly linked marker, and produced convincing evidence that this was not the CMO gene. Incidentally, this Paget?s disease gene homologue is present on canine chromosome 1 and, with information developed from other projects in the lab, we have prepared a very good comparative map of this entire chromosome including a new type of marker that we are now using as part of our whole genome scanning method (a fuller update of the new marker work and the genome can will b given later). This greatly improved map will be useful for future disease gene searches on the largest of the dog chromosomes. We are preparing a manuscript for scientific publication that will include an acknowledgement of the CHF and the clubs for supporting the work in the Paget?s disease gene region.
Since the discovery of the original Paget?s disease gene, several other genes that cause human Paget?s disease have now been found. One of these is the SQSTM1 that is on chromosome 5 in humans that we mentioned in our last report. We are still in the process of finding a genetic marker in or near this gene. The recent availability of DNA sequence fragments as part of the current effort to sequence the whole dog genome (being done at the Whitehead Institute at the Massachusetts Institute of Technology) should make this effort easier. This same sequence information will be used to develop markers in or near the canine equivalents of the other human Paget?s disease genes. We are also examining candidate genes that are involved in bone metabolism that have come to light from three new reviews on bone cells and skeletal defects. The most likely candidates will be chosen from these reviews and tested for causation of CMO. Again, the canine genome sequence information that has become available within the last few months will make this task much easier.
Also as mentioned above, we are continuing our effort on a whole genome scan of the canine genome for a linked marker to the CMO gene. In order to increase the efficiency of the scan, we are developing a map of the genome based upon a type of marker called the single nucleotide polymorphism (SNP for short - pronounced snip). these markers are technically easier to use, and will eventually be automated to improve canine researchers? ability to screen for this and other disease genes of interest to the breed clubs. We currently have about half of the markers needed to span the whole genome and we plan to produce the rest in the near future. We are already using these markers as they come online to search for the CMO gene. The other half is partially developed. To date we estimate that we have covered about 40 to 50% of genes contained in the dog genome, but we have not found a linked marker yet. We are continuing on to screen the other half of the genome. The whole genome scan method, while more certain to find the gene, is very labor intensive and so we will continue to use the candidate gene approach in parallel in the hopes that we will be fortunate and find a shortcut to locating the gene compared to the whole genome scan. Also, the candidate gene approach, if successful, is likely to identify the causative gene directly, in which case finding the mutation and developing a carrier test will be faster. If the whole genome scan method finds a linked marker first, then it will be necessary to determine which of perhaps 50 genes in a given chromosomal region is the causative one before we can identify the mutation and develop the carrier test.
