Does your dog have serious dandruff, excessive scaling, or cracked skin? It may be due to a skin disorder called ichthyosis. While ichthyosis may be cosmetically unappealing, it may also cause considerable discomfort and lead to other systemic concerns.
There is considerable ongoing research into skin disorders with both known and unknown genetic causes, and Embark can test for genetic variants known to cause ichthyosis in a variety of breeds. Genetic testing can confirm (or rule out) the presence of a specific inherited disorder,providing you and your vet with a starting point for possible treatments.
We asked our veterinary geneticists to provide background on ichthyosis and the larger group of genetic disorders that affect keratinization (a process by which skin cells differentiate from one form to another) which are referred to as disorders of cornification (DOC).
Why is proper keratinization important?
As the largest organ in the body, skin protects the body from infection, allergens, pollutants, and UV light, and it plays a vital role in preventing dehydration. Any disorder that impairs skin anatomy or function or an injury to the skin can lead to systemic illness.
Causes of improper keratinization
Disorders of cornification are divided into primary and secondary causes. In primary cornification disorders, the excessive scaling is due to a direct defect in the formation of the outer skin layer (stratum corneum). Secondary disorders are those where excessive scaling develops as a result of another condition (parasites, cancer, endocrinopathies).
Primary disorders are generally diagnosed by ruling out all secondary causes, clinical presentation and/or age of onset, or skin biopsy. Additionally, genetic variant testing can be used to rule in or rule out known inherited causes of primary cornification disorders. Most known genetic disorders are autosomal recessive (two copies of the variant are needed to exhibit clinical signs), and there is no sex predeliction for the variant. Genetic testing can help prevent carrier dogs being bred to each other unknowingly.
Ichthyosis is derived from the Greek root “ichthy,” meaning fish, and was so named due to the visible scales on the skin. Ichthyotic dogs typically have large, greasy flakes of dandruff, but aren’t itchy. The scales of skin can get so thick that they can crack and cause uncomfortable fissures. Typically, clinical signs develop in puppies, but the disease tends to worsen with age.
Ichthyosis can be epidermolytic (EI) or nonepidermolytic (NI), which is determined based on the microscopic appearance of the skin. Dogs affected with epidermolytic ichthyosis have multiple regions of pigmented scale with alopecia (hair loss) and roughening of the skin. The condition corresponds to a defect in keratin formation, and is the noted form in the Norfolk Terrier and Cavalier King Charles Spaniels, although it has been sporadically described in other breeds like the Rhodesian Ridgeback and Labrador Retriever.
Nonepidermolytic ichthyosis, which can cause skin lesions and inflammation, has been documented to affect Jack Russell Terriers, Golden Retrievers, and American Bulldogs.
- Golden Retriever ichthyosis: This form of ichthyosis is generally considered “mild” although severity can be dog-dependent. Affected dogs develop a large, soft, whitish scale that is typically present on the trunk and may develop increased pigmentation of the ventrum (lower abdomen). Golden Retrievers are typically diagnosed at less than one year of age; however, adult-onset cases are not uncommon. Physical manifestations may wax and wane, and some dogs develop secondary bacterial skin infections that may confound a diagnosis. Learn more.
- American Bulldog ichthyosis: This form of Ichthyosis is pathologically similar to that of Golden Retriever ichthyosis but is more severe and does not wax and wane. American Bulldogs consistently develop clinical signs at an extremely young age (typically before weaning). Young puppies have a scruffy/disheveled haircoat, red skin, and tightly adherent light brown scale, which gives the abdominal skin a wrinkled appearance. In adult dogs, the entire abdomen, armpits, and groin have a reddish-brown discoloration, and thickening of the footpads or scales through the haircoat may be observed. Yeast overgrowth on the skin may be severe and can lead to ear infections and infection of the feet which may be confused with non-seasonal atopy (inhalant allergy).
- Jack Russell Terrier ichthyosis: Nonepidermolytic ichthyosis in Jack Russell Terriers is characterized by large, thick, adherent parchment paper-like scales. This is generally more severe, and these dogs also develop yeast infections of the skin which are extremely itchy.
- Cavalier King Charles Spaniel dry eye curly coat syndrome: In addition to scaling with increased pigment on the abdomen, Cavalier King Charles Spaniels develop keratoconjunctivitis (dry eye with inflammation), a roughened/curly hair coat, foot pad thickening, and nail abnormalities.
- Ichthyoses not yet characterized: A number of other breeds such as Soft-Coated Wheaten Terriers, West Highland White Terriers, English Springer Spaniels, and Labrador Retrievers have been diagnosed with NI, but further molecular characterizations have not been documented in the literature.
For what conditions are genetic variant tests available?
Genetic testing can help you and your veterinarian determine if your dog has a genetic variant for ichthyosis, so you can stay ahead of the condition.
Some examples of genetic skin conditions for which Embark tests are ichthyosis: PNPLA1 in Golden Retrievers, NIPAL4 in American Bulldogs, and SLC27A4 in Great Danes; ichthyosis, epidermolytic hyperkeratosis (KRT10) in Norfolk Terriers; congenital keratoconjunctivitis sicca and ichthyosiform dermatosis, dry eye curly coat syndrome, (FAM83H) in Cavalier King Charles Spaniels.
Each condition has a unique presentation and can affect the skin, coat, nasal planum and/or footpads (learn more here). Recently, two additional causative variants have been published: ASPRV1 in German Shepherd Dogs and TGM1 Jack Russell Terriers. To learn more about how you can help Embark offer these tests, contact us.
Embark also offers genetic testing for variants that can cause other skin abnormalities like hyperkeratosis, parakeratosis, and skin fragility syndromes.
How are DOCs diagnosed?
For dogs showing signs of a skin disorder, the first step in diagnosing ichthyosis (and other DOCs) is for a veterinarian to examine the characteristic lesions. He or she may perform blood work (complete blood count and serum chemistry), a skin scrape, skin cytology, dermatophyte (ringworm) culture, skin biopsy, +/- a urinalysis or specific endocrine testing. Genetic testing can also be done to confirm—or rule out—an inherited condition.
Genetic testing is an easy and non-invasive way to potentially make a diagnosis of a skin condition that may clinically present like many other things, including: allergies or a cutaneous drug reaction, parasites, infection, exposure to excessive UV light, endocrinopathies (Cushing’s disease, hypothyroidism), autoimmune disease, epidermolysis bullosa, lethal acrodermatitis, vitamin and mineral deficiencies, sebaceous gland abnormalities, primary seborrhea, cancer, and dermatomyositis.
Treatments for ichthyosis
There is no cure for ichthyosis; the treatments of choice are topical therapies such as specialized shampoos, moisturizing rinses, agents to remove excessive scale or to restore the skin barrier and thus prevent water loss, and topical medications to address secondary infections.
Therapy must be tailored to the individual patient, and care should be taken not to damage or irritate the skin. Some dogs may benefit from oral essential fatty acid (EFA) supplementation or oral medications to treat infections. Additionally, a novel topical therapy is under investigation to reinstate the corneocyte lipid envelope (CLE). Your veterinarian can provide more information regarding which products and treatment schedule is appropriate for your dog.
Ichthyosis: The human connection
Ichthyosis affects humans, too: It affects people of all ages, races, and genders. The disease usually presents at birth, or within the first year, and continues to affect the person throughout their lifetime. Learning more about inherited Ichthyosis in dogs may help scientists develop treatments for humans. In the meantime, a variety of organizations are working to unite affected children with affected dogs for emotional support.
In both veterinary and human medicine, significant therapeutic research into disorders of cornification is underway, in the hopes of restoring the barrier function of the stratum corneum and decreasing inflammation and overproduction of cells.
At Embark, we continue to work with our partners to support research into skin disorders with unknown genetic variants, as part of our commitment to improve the lives of dogs everywhere. To learn more about the variants Embark tests for, click here. If your dog suffers from a skin condition with a known genetic variant that Embark does not offer, contact us to learn how to help Embark offer this test.