Nog een test

[Laboriginals]

Er is nog een nieuwe test op de markt. Genoscoper in Finland biedt de DLA diversity test aan. Deze is voor alle rassen. Hij meet het aantal verschillende haplotypes die van invloed zijn op het immuunsysteem. Deze test is in eerste instantie niet zo interessant voor individuele fokkers. Eigenlijk zouden rasclubs in diverse landen de situatie van hun populatie moeten testen. Dan pas kan je als individuele fokker je eigen hond(en) testen en de uitkomst vergelijken met de gemiddelde situatie.

Dit is de toelichting:

DLA diversity test to follow and maintain heterozygosity at MHC II locus

Much of the genetic diversity of dogs is diminished or lost in many breeds due to aggressive breeding programs and closed inbred populations. Loss of genetic diversity threatens the welfare and vitality of dogs and may predispose them to various diseases.

An important part of this genetic diversity is related to genes which are responsible for the effective and functional immune defense against viruses, parasites and other foreign pathogens in dogs. There are probably hundreds if not thousands of genes involved in the functionality of the immune system in mammalian genome. One of the most important gene clusters is called major histocompatibility complex (MHC). MHC complex includes a large number of genes and it located in the canine chromosome 12.

This MHC complex includes genes that are responsible for the recognition of the species own tissues from foreign material. Recognition is related to the genetic diversity and some of the genes in this region contain particulary hypervariable areas in their coding regions to maintain them as diverse as possible. The loss of diversity in the MHC region or inheritace of particular allele combinations may result in increased susceptibility to autoimmune diseases such as diabetes, atopia, hypothyroiditis and different forms of inflammatory disorders. Many canine autoimmune disorders have been already associated with risk haplotypes in the MHC locus and homozygosity to risk alleles or haplotypes seems to increase the disease risk. Heterozygosity is preferred in the MHC locus in wild population too. Several studies in both natural and domesticated populations underline the importance of heterozygosity rather than the number of different haplotypes in the MHC region.

We have now tools to type your dog’s MHC II genes (DLA typing) so that you can follow the diversity of your dogs and lines and use this information while planning future breeding. It is useful to have a DLA-profile from your breed in different countries since the frequency of the alleles in the MHC genes may vary a lot between populations. Once the DLA-profile is established you can compare your dog's profile for the overall breed' or line's profile and take it into account while planning future breeding. The aim is to maintain the heterozygosity of the MHC region as much as possible in the breeding lines. This should reduce the risk of autoimmune diseases and other diseases.

As a general rule it may be wise to avoid increasing homozygosity in the MHC locus containing a large number of important genes. There is growing amount of evidence that homozygosity in the MHC locus increases the risk for autoimmune disorders. Many of the published studies include rather small sample numbers. This has effects on the strength of the risk factors and significance levels. Larger studies in future should give more accurate risk estimates not available yet. However, it may be wise to choose a breeding partner that has different haplotypes to maintain heterozygosity and diversity in your litters and lines.

MHC locus is a functionally important locus and it is constantly under a selective pressure. Certain MHC haplotypes may not be allowed at all or may lead to inviability. With DLA diversity testing we can analyze only MHC locus in one chromosome. Although it provides important data that may also reflect the overall diversity, it is recommended that breeders would also test other markers from other chromosomes to get a better picture of the overall diversity of the breed. Due to selective pressure the diversity of the MHC locus may turn out to be more heterozygous than other parts of the dog's genome.

It is important to remember that several factors need to be considered in breeding decisions and DLA results are only one factor among others. Breeding plans should never be based only on DLA types or any other genetic tests. Breeding decisions need to be made on case-by-case basis. This is an increasing challenge in the future taking into account the growing number of genetic tests. Breeding against one locus may cause trouble in other loci which are not known yet. Maintenance of the genetic diversity in the breed should be the key consideration in breeding plans. A good choice for this is to avoid inbreeding and keep the inbreeding coefficient as low as possible. This should also maintain the MHC locus heterozygosity.

DLA profiling service for Breed Clubs

Before typing individual dog's it would be useful to have a public DLA profile for the breed. Different breeds have different numbers of MHC II haplotypes based on the origin and history of the breed and breeding choices made in the past. The current DLA profile of the breed can be investigated only by DLA typing. We provide DLA-profiling services for Breed Clubs. We suggest to type about 50-100 unrelated dogs provided by the owners or the Club. After the analysis the Breed Club will get haplotype profiles and frequencies. This information can be used to advise the breeders to aim at better and healthier breeding choices. The DLA profile service takes usually at least 2-3 months to complete.

If your Club is interested in this service, please contact our Customer service. Several Clubs have already successully profiled their breeds with us.