How do I interpret the results of the genetic test correctly?

An important basis for the evaluation of genetic test results is an understanding of the complex relationship between the test result (the genotype) and the effect on the animal (the phenotype). Not every genetic variant necessarily leads to a disease or manifests itself in an external characteristic. This makes the interpretation of test results a challenging task.

Monogenic (determined by only one gene) genetic variants represent a comparatively simple case and can be dominant or recessive. In the case of recessive inheritance, a dog must carry two copies of the mutated gene variant (homozygous) – i.e. inherit one from each parent – for the disease or trait to become pronounced. Dogs with only one copy (heterozygous) are Investment carrier. You bremain healthy themselves or show no change in the trait, but can pass the variant on to their offspring. In the case of dominant inheritance, one copy of the mutated variant is sufficient for the trait or disease to manifest itself. Dominantly inherited diseases usually occur in every generation, while recessive diseases often remain hidden until two carriers are mated.

Many characteristics do not follow these simple rules (see info box 2). When the interaction of several genes together influences the expression of a trait or a disease, this is called polygenic inheritance. Examples are often found in coat colors, which are controlled by many different genes. Variable expressivity describes the phenomenon that although a genetic variant leads to a certain trait or disease, the degree of expression can vary from animal to animal. However, many hereditary diseases also exhibit polygenic inheritance and their development is often additionally influenced by environmental factors (multifactorial diseases). There is also incomplete penetrance. This describes that not every dog that carries a certain genetic variant will actually develop the corresponding disease or trait. Some animals remain symptom-free despite the mutated variant.

Sometimes genetic risk factors are also tested. These are genetic variants that are associated with an increased probability of the expression of symptoms of a disease or a certain trait, but are not causal.

A complex example can be found in the IVDD risk (Hansen’s Type I Intervertebral Disc Disease). The typically short leg length of many breeds is either caused by chondrodysplasia (CDPA) or can result from chondrodystrophy (CDDY). However, only CDDY is associated with an increased risk of IVDD (herniated disc) in some dog breeds. Scientific studies are currently underway at various international research institutions to determine the exact health effects of CDDY, its varying significance in different dog breeds and to identify other genes relevant to the risk of disc herniation.

Why is the breed-specific evaluation of genetic test results important?

Genetic variants can have different effects in different breeds. A mutation that correlates with a certain disease in one breed can occur in another breed without dogs carrying the variant mixed or homozygous becoming ill. One example is neuronal ceroid lipofuscinosis (NCL) in American Staffordshire Terriers. Clinical symptoms include an increase in physical restlessness and aggressiveness. The dogs become hyperactive and suffer from epileptic conditions. The age at which the disease begins and its severity can vary greatly. The genetic variant can also occur in other breeds, but a correlation with NCL is not scientifically known.

Conversely, different genetic variants can also be responsible for the same disease depending on the breed. In addition to the disease-causing variant for the American Staffordshire Terrier, for example, several other variants are known for NCL that can lead to NCL in other breeds.

The frequency and significance of certain genetic risk factors also differ between breeds. In XXL screenings in particular, there is a high probability that tested animals carry some variants in their DNA that are known to cause disease in other breeds.

One example is color mutant alopecia (color dilution alopecia/CDA). Among other things, this disease leads to progressive hair loss due to a disruption in pigment formation and storage. It is scientifically known that there is a connection between dilution, coat color and CDA. Dilution is not the cause of CDA and not every dog with dilution is affected by CDA, but there are specific breeds at increased risk. Weimaraners are dilute, but, like Great Danes of the blue color, do not appear to contract CDA. In Dobermans with CDA, however, the proportion of dilute dogs was very high, which resulted in the blue color being removed from the FCI breed standard, so it is essential to always interpret test results in the context of the respective breed in order to make well-founded breeding decisions and avoid misjudgments. With every genetic test – be it an individual test, breed package or the comprehensive XXL screening – breeding clubs and the specialist advice of the laboratories can help to classify the results correctly. A heterozygous or homozygous test result does not automatically mean a case of disease or that breeding will be ruled out.

What should you look out for when choosing a provider of genetic tests for dogs?

Genetic test packages such as the inexpensive LABOGenetics XXL dog screening are very much in vogue, which increases the importance of quality assurance. LABOKLIN sets the highest standards. As an accredited specialist laboratory, we use standardized procedures and offer expert advice from experienced specialists. These quality features are crucial when choosing a test provider in order to guarantee reliable and meaningful results. The investment in genetic testing pays off in the long term – through healthier animals, the avoidance of hereditary diseases and sound breeding planning.