Background
The CSNB test is a DNA-based test that provides a method to unequivocally identify Congenital Stationary Night Blindness, or CSNB. As an effect of the disease, affected horses are suffering from night blindness, and may have weak vision during the day. The amount of deteriorated vision may differ largely between horses. In addition to reduced vision, affected horses also show abnormal electroretinogram (ERG).
During the last decades, a large number of scientific publications have described the genetic principles of coat colour and coat variation. Coat colours and coat variations are influenced by many hereditary factors. The DNA-tests are based on physiological effects in the body, in which the production and distribution of pigments result in many coat colour variants. In several cases, the coat colour of an animal may only be decided using DNA-tests.
The Appaloosa spotting pattern, also known as Leopard Complex spotting (LP) includes a highly variable group of white spotting- or depigmentation patterns in horses. Appaloosa horses have three additional identifiable characteristics: mottled skin around the muzzle, anus and genitalia, striped hooves and white sclera round the eyes. The Appaloosa pattern is the result of an incompletely dominant mutation in the TRPM1 gene, also known as the LP gene. The LP gene allows for the expression of the various leopard complex spotting patterns while other genes determine the extent (or amount) of white. The CSNB / Leopard Spotting test (P311) tests for the status of the LP (TRPM1) gene. This gene has two variants (alleles). The allele LP is incomplete-dominant and expression of the Appaloosa pattern is variable, ranging from absent to extremely white patterning. At least one copy of the LP allele allows the expression of the Appaloosa pattern. The amount of white present is not dosage related, horses with two copies of the LP allele can have minimal expression of white patterning. The recessive allele N does not have an effect on the basic colour. The variability in the amount of white on Appaloosa-coloured horses is controlled by other genes, one of which is PATN1. Horses that have one copy of the LP allele, in combination with at least one copy of the PATN1 allele most often have a Leopard or a near Leopard pattern. Horses that have two copies of the LP allele in combination with at least one copy of the PATN1 allele most often have a Few-spot or near Few spot pattern. Horses that have two copies of the LP allele suffer from Congenital Stationary Night Blindness (CSNB), which is the inability to see in low to no-light conditions.
Test specific information
Since 2015, two brands have been developed. CombiGen? is mainly directed at veterinarian applications, whereas CombiBreed? is mainly directed at breeders and/or owners. Detailed information about Coat Colours and Coat Variation is presented at www.pharmaDNA.com.
Age
The disease may show itself on different ages, in which it cannot be estimated when the first symptoms may show themselves. Differences may exist between littermates, and between breeds.
Throughput
Normally the result can be expected within 25 working days. This turn-around-time starts when both the sample and the fully filled-out and signed submission form have been received.
Location of disease or trait
This disease mainly affects vision, and may result in blindness.
Breed dependence
This DNA test is available for the following breeds: Appaloosa, Miniature Horse.
Sample type
For this DNA test we accept the following materials: Blood EDTA, Blood Heparin, Semen, Hair, Tissue. Please contact PharmaDNA if you wish to submit other material as listed.
Result
An animal can be free and has in that situation two healthy alleles. When used in breeding this animal will not become ill due to the disease. It cannot spread the disease in the population.An animal can be carrier and has in that situation one healthy and one disease allele. When used in breeding 50 percent of the offspring will receive the disease allele. Carriers will not become ill.An animal can be affected and has in that situation two disease alleles. When used in breeding all offspring will also receive the disease allele. Affected will become ill.
Inheritance
This genetic factor is inherited in an autosomal, recessive, mode. This means, that the individual can be free of the disease (homozygote normal), affected (homozygous affected) or carrier (heterozygous). Carriers may spread the mutation in a population without showing symptoms themselves. Because of this, it is extremely important to identify carriers correctly to prevent spreading of a mutation.
Severity of Disease
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