Ichthyosis (Golden Retriever type)
Written by Arielle Hébert, Animal Health Technician
(Translation DR)
Ichthyosis is the name given to a family of genetic diseases that affects the skin of several species of animals including humans and dogs. The word “Ichthy-” in Greek means “fish”. This family of genetic diseases has been given this name because it gives the skin a scaly appearance, like that of a fish. Among the dog breeds most affected by ichthyosis are the Golden Retriever, American Bulldog, Jack Russell Terrier and Norfolk Terrier. For the Golden Retriever in particular, ichthyosis is one of the most common genetic diseases in the breed, especially in North America and Europe.
Clinical Signs and Diagnoses of Ichthyosis
Ichthyosis is characterized by dry, thickened, scaly skin that forms plaques (scales) of different sizes. The plaques may become whitish or blackish in colour during the disease process. The skin is rough to the touch. Golden Retrievers with ichthyosis will have these patches on the skin, especially on the stomach and chest.
Dogs with the disease will begin to show clinical signs between a month to a year and a half of age. In most cases, ichthyosis will be present for the entire life of the dog. The plaques on the dog’s skin are also a gateway for many microorganisms such as bacteria and parasites. In the clinic, the veterinarian can do a skin biopsy and a histological examination. In addition, he can check for the presence of parasites by scraping the affected area.
Treatment
As mentioned earlier, when a dog has ichthyosis, in the majority of cases, he will have it for the rest of his life. In other words, the disease itself is incurable. However, there are treatments that will help improve the animal’s condition.
Brushing the coat on a regular basis can help the dog. Certain keratomodulator shampoos can also decrease the extent of plaques on the dog’s skin. Emollients are also good treatment options, as is food high in fatty acids. These are all supportive treatments and they are only intended to improve the health of the dog through better hygiene. The veterinarian will also be able to help choose the best options depending on the extent of the symptoms of the dog.
The Genetic Profile of Ichthyosis
Ichthyosis is a genetic disease with autosomal recessive inheritance. The term autosomal means that the disease is not related to the sex of the animal: both males and females can be affected. Recessive means that it takes two mutations, one in each copy of the gene in question, for the animal to develop the disease.
Ichthyosis in Golden Retrievers is caused by a mutation in the PNPLA1 gene, which is found on canine chromosome 12. The mutation is a deletion plus an insertion of DNA into the gene which produces a defective protein. The effect of this deficit in the skin cells is ichthyosis. Through studies of ichthyosis in the Golden Retriever, mutations in the same gene (PNPLA1) have been identified as one of the genetic defects responsible for ichthyosis in humans.
Mutation Frequencies
At the Laboratory of Veterinary Genetics, we have tested over 200 Golden Retrievers for the mutation that causes ichthyosis. The results show us that 49% of the Golden Retrievers tested were “clear” (N/N, which does not carry a copy of the mutation). On the other hand, 39% of Golden Retrievers we tested were carriers (M/N) and 12% of Golden Retrievers tested were double mutated (M/M). In other words, according to our sampling, 12% of Golden Retrievers are at risk of developing ichthyosis.
To compare with the results of the Orthopedic Foundation for Animals (OFA), the percentage of Golden Retrievers that are clear (N/N) is 73%, the percentage of Golden Retrievers that are carriers (M/N) is 25% and the Golden Retrievers that are at risk (M/M) is 1.9%. This tells us that the majority of Golden Retrievers in the population are free from the genetic mutation. On the other hand, there is a large percentage (between 25% to 39%) of animals carrying the mutation.
Mating strategies
As much as possible, it is best to breed Golden Retrievers that are not carriers (M/N) of the disease. Otherwise, for every puppy in the litter, there is a 1 in 4 chance that the puppy will be double mutated (M/M). The puppies who have received 2 copies of the ichthyosis mutation (M/M) will be at risk of developing the disease.
However, it is possible to breed a carrier dog (M/N) with a clear dog (N/N). Nonetheless, even if carriers (M/N) are not at risk of developing ichthyosis, the goal is that one day, the genetic mutation will no longer exist. Therefore, the fewer carrier dogs (M/N) there are in the population, the better we can control the frequency of the disease. To keep the rate of carrier (M/N) and double mutated (M/M) dogs low, it is important to have the breeders tested.
Ichthyosis in other dog breeds
As mentioned earlier in this text, ichthyosis is a disease that can affect dog breeds other than the Golden Retriever. Indeed, this skin disease is also found in the American Bulldog, the Bull Terrier, the Cavalier King Charles Spaniel, the Long-haired Collie, the Great Dane, the English Springer Spaniel, the Norfolk Terrier, the Miniature Pinscher, the Labrador Retriever, the Jack Russell Terrier, Rottweiler, Irish Setter, West Highland White Terrier and Yorkshire Terrier. For the American Bulldog, Jack Russell Terrier and Norfolk Terrier, the mutation responsible for ichthyosis is characterized and for each breed the mutation is found in a different gene. So, when it comes to testing ichthyosis in these breeds, it is very important to do the right DNA test for the right breed of dog to make sure you get the pertinant results.
References:
- OMIA link: [1588-9615]
- Grall A, Guaguère E, Planchais S et al. (2012) PNPLA1 mutations cause autosomal recessive congenital ichtyosis in golden retriever dogs and humans. Nat Genet. 44(2) : 140-7 [pubmed/22246504]
- Guaguere E, Bensignor E, Küry S, et al. (2009) Clinical, histopathological and genetic data of ichthyosis in the golden retriever: a prospective study. J Small Anim Pract. 50(5):227-35. [pubmed/19413748]
- Puigdemont A, Furiani N, De Lucia M et al. (2018) Topical polyhydroxy acid treatment for autosomal recessive congenital ichthyosis in the golden retriever: a prospective pilot study 27(4):306-e75 [pubmed/29786154]