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Phenotype: Skin condition that results in a mild to severe scaling of the skin, usually excluding the head, extremities, paw pads, and nose. Scales become pigmented, progressing to gray or black, and range in size from small to large. These scales may give the dog’s hair and skin a “dirty” look as the scales progress to a darker color.
Mode of Inheritance: Autosomal recessive
Alleles: N = Normal, Ich3 = congenital ichthyosis 3 allele
Breeds appropriate for testing: Labrador Retriever, Labradoodle, Labrador-Golden crosses, other Labrador Retriever crosses.
Explanation of results:
• Dogs with N/N genotype do not have this congenital ichthyosis 3 allele.
• Dogs with N/Ich3 genotype are carriers of the congenital ichthyosis 3 allele found in Labrador Retrievers but will not develop ichthyosis. If two carriers are mated, approximately 25% of the puppies are predicted to develop disease and 50% are predicted to be carriers.
• Dogs with Ich3/Ich3 genotype are homozygous for the congenital ichthyosis 3 allele found in Labrador Retrievers and are expected to develop ichthyosis, although the presentation may be variable.
Ichthyoses are a group of genetic skin disorders characterized by defects in the formation of the stratum corneum (the outer layer of the epidermis) that result in scaling of the skin and desquamation (shedding of the outer layer of the skin, or more colloquially, skin peeling). Symptoms of ichthyosis include mild to moderate generalized scaling on the body, usually excluding the head, extremities, paw pads, and nose. The scales are initially a whitish color but become pigmented, progressing to gray or black, and can range in size from small to large. These scales may give the dog’s hair and skin a “dirty” look, especially as the pigmented scales shed and adhere to the coat. Age of onset is generally early: clinical signs have been detected as early as 3-6 weeks of age in some dogs, although in others, the signs may not become readily apparent until months or even years later.
In humans, over 30 different genes that result in various ichthyoses have been identified. In dogs, at least 12 different breed-specific types of ichthyosis have been described, but genetic mechanisms have only been identified in a few breeds. Two alleles have been identified as correlated with the congenital ichthyosis disease seen in Golden Retrievers. Researchers proposed that congenital ichthyosis caused by the PNPLA1 variant in Golden Retrievers be referred to as congenital ichthyosis type 1 (ICH1) and that caused by the ABHD5 variant also in Golden Retrievers be called congenital ichthyosis type 2 (ICH2).
A third allele associated with congenital ichthyosis in the Labrador Retriever was recently discovered by Dr. Tosso Leeb and colleagues. Congenital ichthyosis caused by this allele is referred to as congenital ichthyosis type 3 (ICH3). Once the findings have been published, we will update this page with additional information about the study.
Congenital ichthyosis in the Labrador Retriever is inherited in an autosomal recessive fashion. Two copies of any of the alleles must be present for the disease to manifest, and both sexes are equally affected.
Testing recommendations: Testing for this allele can assist veterinarians with diagnosis and help breeders identify carriers among breeding stock to select appropriate mates that will reduce the risk of producing affected offspring. To avoid the possibility of producing affected puppies, matings between known carriers is not recommended. Dogs who genotype as Ich3/Ich3 should be clinically evaluated.