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Thanks to vaccination and new treatments bacterial and viral diseases have been controlled. Modern day vets see far more dogs suffering from genetic disorders. A genetic disorder results from an abnormality in the genome of the individual, inherited or in which inheritance seems to play a major role. These genetic disorders are quite frequent in purebred dogs. Almost 480 inherited diseases have been identified in the dog. Whereas in human inherited diseases frequency does not exceed 0,1%, many canine inherited diseases have a frequency going from 10 to 50% in the affected breeds. There is an urgent need for tools reducing the frequency of inherited diseases in the dog population and this will be one of the first achievements of the LUPA project

How to reduce inherited disorders?

The frequency of inherited conditions can be reduced through good breeding practices. For this to occur, we need to know:

• How the disease is inherited (the mode of inheritance): For many disorders that are believed to be inherited, the specific pattern of inheritance has not been established. Breeds that have an increased risk for a condition, relative to other dog breeds, are said to have a breed predisposition.
• How to identify the condition as early as possible
• Ways to recognize carriers of the disease who are not clinically affected: DNA-tests are excellent tools because they can be used early in the animal’s life span (starting at birth) and they allow an unambiguous screening of carrier animals. Preferably, affected dogs and their close relatives should not be used in breeding schemes.

What is a gene, a mutation and a DNA test?

DNA is a large molecule comprised of four basic units linked together in a long strand. If we assign each unit a letter, then we can envision the chromosome as a long string of letters. Genes can be thought of as long words scattered along the chromosome. These words have special meaning to the worker molecules in the cell, and encode a set of instructions as to what they are to build. Any mistake in a word scrambles the instructions, and either the workers in the cell make no product or a defective one is made. These mistakes in genes are known as mutations.

There are basically two kinds of mutations, dominant and recessive. Every cell in the body (except sperm and eggs) has two copies of each gene (one from the sire, and one from the dam). A dominant mutation is where one defective copy of a gene is enough to affect the individual, whereas a recessive mutation requires that both copies of the gene carry a mutation for the individual to be affected. Many dog genetic disorders have a simple recessive mode of inheritance but some are more complex, being caused by problems in more than one gene, so called polygenic diseases. Conditions like cancers, heart diseases, immune disorders and epilepsy are polygenic. These polygenic conditions are also influenced by environmental factors. Most of the diseases studied in this project belong to this last category.

DNA tests

In case the exact mutation is known, the diagnosis is accurate. The portion of the gene surrounding a mutation can be synthesized readily in the laboratory by a process called PCR (polymerase chain reaction). This method allows specific regions of the genome to be amplified from a small sample, and the DNA can be analyzed quickly. DNA samples for individuals can be obtained from any cells. They are easily obtained by taking a small blood sample or by scrapping a few cells from the inner cheek.

The second way to identify mutations is known as linkage. A linked marker is a DNA region close to the genetic defect that co-segregates with the deficient gene. The closer that the marker is linked to the disease, the more accurate the test.

What the future holds?

The area of genetic testing in dogs is very active. The goal of this European project is to discover specific canine genomic regions associated with polygenic diseases. This will lead to the development of DNA linkage tests to detect dog carriers. Progressively we will determine the exact mutation(s) associated with the disorders and check if human homolog mutations exist and can explain similar human diseases.

List of Breeds followed within LUPA

List of Diseases followed within LUPA

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Last Updated Tuesday, 04 November 2008 21:04