The field of molecular genetics has made significant strides in analyzing hereditary skin disorders over the last several years. This paper is a critical review of the scientific literature in this area with the view to update the available genetic tests for skin diseases in cats, dogs, and horses. In addition, the purpose was to inform the veterinary practitioner about which genetic tests are appropriate for selection and application.

Any trait of a living organism is under the control of genetic factors and/or the environment. Some traits are controlled exclusively by the environment and others are determined exclusively by genetic factors. Most skin diseases are determined by a combination of both factors. Usually, traits that are exclusively controlled by genetics show a monogenic mode of inheritance (a single gene determines whether the trait is expressed or not). Currently, genetic tests are most relevant for this mode of inheritance yet it is expected to become increasingly important for complex diseases in the future.

Purebred animals are much less heterogeneous than in humans. Therefore, in the case of many hereditary diseases it is found that all affected individuals of one breed carry the same deleterious mutation. Yet, one should remember this is not an absolute rule and that genetic tests now available usually interrogate a single position on the genome. A positive test result clearly establishes the diagnosis, but a negative test result only excludes one particular genetic mutation, but not other unknown mutations which may very well be located in the same gene. It is best to interpret negative results with care. Also, if a genetic test works in one breed, it does not mean the test will work in other breeds.

With the advances in molecular genetics, it is now possible to sequence the entire genome of a patient at an affordable cost. The technology along with other tools significantly allows the identification of the causative DNA mutation underlying such heritable phenotypes. Where it required relatively large sample numbers of animals in the recent past, these advances in technology now allow for investigation of a single-family or even an isolated individual.

In this paper, nine different genodermatoses and hair morphology traits with known causative genetic variants in cats were noted in a table. Two traits were genodermatoses involving the Birman (hairlessness with short life expectancy) and Sphynx (hairlessness). The remaining seven traits were related to hair morphology regarding long hair or curly hair traits. All but one trait was autosomal recessive. The curly hair coat trait of the Selkirk Rex was autosomal dominant.

Genetic tests are more and more important as a diagnostic tool in veterinary medicine. They can aid in establishing a diagnosis when a disease with fairly nonspecific signs. These genetic tests are also important for sustainable breeding programs and decrease the numbers of animals with such hereditary diseases.

Genetic testing is expected to become a more routine part of veterinary practice. Understanding the proper selection and application of the test results is important for veterinarians. The authors advise consulting a veterinary geneticist if a new genodermatosis is suspected. (VT)