Ichthyosis in dogs – inherited scaling and skin care

Overview

Ichthyosis is a group of conditions in which the outermost protective skin layer, the stratum corneum, does not form or renew normally. In healthy skin, dead surface cells shed unnoticed and are replaced by new cells moving upwards from below.

The stratum corneum normally contains around 20–30 layers of cells, whose tightly packed structure helps protect the dog from the environment. The disease's name refers to fish scales because the flakes can look like a scaly surface.

However, not all scaling is ichthyosis: allergies, external parasites, hormonal conditions and metabolic diseases can cause similar changes. In a Golden Retriever, skin signs may become much milder at times and worsen again later in the same dog's life.

Connections between the surface skin cells hold the stratum corneum together before the cells shed normally.

Based on microscopic changes, ichthyoses are divided into epidermolytic and non-epidermolytic forms: those that cause cell damage and those that do not.

Causes

The barrier lipids and cell shedding are disrupted

The function of the stratum corneum depends both on the structure of its surface cells and on the lipid layers that form between them. A genetic defect can affect a structural protein, an enzyme or lipid formation, so the different ichthyoses do not all share the same mechanism.

The common type in Golden Retrievers results from a change in the PNPLA1 gene, which disrupts lipid metabolism in the surface layer. The abnormal lipid layer impairs formation of the barrier between cells and alters the normal shedding of dead skin cells.

In another form in Golden Retrievers, the change affects the ABHD5 gene, whose product also helps form the skin's protective lipids. These Golden Retriever forms are called types 1 and 2, and testing for the first type does not automatically cover the second.

Both Golden Retriever forms are inherited recessively: the disease-causing change has been inherited from each parent. However, the same inheritance pattern cannot describe all canine ichthyoses, as a dominantly inherited form has also been identified in German Shepherd Dogs.

Disruption of the stratum corneum can trigger a repair response in which the surface cell layer thickens and lipid production changes.

In the epidermolytic form, damage within cells can lead to tiny blisters in the surface layer of the skin.

Risk factors

The Golden Retriever is a recognised predisposed breed, but the skin disorder has also been described in American Bulldogs, Jack Russell Terriers, Norfolk Terriers and Great Danes, for example. Signs in Golden Retrievers are often noticed before 1 year of age, but may only become apparent in adulthood.

In American Bulldogs, the first scaling in the coat may be visible as early as 1–2 weeks of age. The original family study of type 2 included both affected males and affected females.

Scaling in Golden Retrievers may start at a few weeks of age or later, but usually begins before 18 months of age. Among 463 Golden Retrievers voluntarily tested in Italy, PNPLA1 testing found that 42% were clear of the change, 37% were carriers and 21% were genetically affected.

These figures describe the tested group, rather than the proportion of all dogs in Italy or other populations with clinical disease.

In the same Italian study, all 45 dogs tested for ABHD5 were clear of the change, so no dogs genetically affected by type 2 were identified.

Typical symptoms

The signs depend on the breed and inherited form, so affected dogs do not all have the same skin appearance.

• Fine flakes or large scales that cling to the skin build up in the coat.

• Initially pale scales may become grey, brown or black over time.

• The sparsely haired skin on the abdomen may feel rough, sometimes like sandpaper.

• In Golden Retrievers, scaling may appear symmetrically in the armpits, on the chest and flanks, and in the groin.

• In Golden Retrievers with type 2, thick white scales may cling to the inner surface of the ear flap.

• In the severe form in Great Danes, the skin may be unusually folded from birth and later become dry and inflexible.

The common form of ichthyosis in Golden Retrievers does not usually cause intense itching, even when scaling is clearly visible. The nose, footpads and ear canals usually remain unaffected in this common Golden Retriever form.

The bare skin on the abdomen may also darken because of increased pigmentation.

Complications and consequences

A damaged barrier can predispose the skin to bacterial or yeast overgrowth and infection. Secondary infection can add itching and discomfort to an otherwise non-itchy Golden Retriever skin condition.

In American Bulldogs, itching is often associated particularly with increased Malassezia yeast on the skin. Barrier damage also increases water loss through the skin, which is a separate problem from visible scaling alone.

In Golden Retrievers with type 2, scales may adhere more firmly and the surface skin layer may be thicker than in the common form. The severe congenital form in Great Danes has a poor prognosis, so the outlook for a mildly affected retriever cannot be applied to it.

A severe bacterial infection can extend into the dermis and increase the risk of bacteria spreading into the bloodstream.

The possible effects of Golden Retriever type 2 on other organs are not yet sufficiently understood.

Diagnosis at the vet

The cause of scaling is investigated before an inherited diagnosis

At the appointment, the vet reviews the age when signs first appeared, the environment, previous topical treatments and any itching. Tiredness, increased drinking or unusual panting also help direct investigations towards other causes of scaling.

The skin examination assesses coat quality and density and whether scaling occurs alongside hair loss, crusts or other changes. Skin scrapings and combing help look for external parasites that might explain the signs or be present at the same time.

Microscopic examination of a surface sample can identify skin yeasts and bacteria before treatment for infection is chosen. A biopsy can assess the structure of the stratum corneum and distinguish conditions such as sebaceous adenitis from other causes of scaling.

In Golden Retriever type 2, tissue samples show particularly marked, plate-like thickening of the stratum corneum. Inflammation in the biopsy may be mild or absent, despite the clearly abnormal surface layer.

If the signs suggest thyroid or adrenal disease, targeted hormone tests are used to investigate their function. Blood and urine tests may show changes that support investigating an underlying hormonal disease alongside the scaling.

A genetic test answers a specific question

A known genetic change can be tested using a blood sample or a swab from the inside of the cheek. Results are classified as clear, carrier or genetically affected, depending on whether the change is present in neither, one or both copies of the gene.

A carrier of one copy of a recessive disease variant is clinically healthy but can pass the change to its offspring. A PNPLA1 result does not reliably predict how severe the signs will be or whether visible scaling will remain as pronounced in adulthood.

The 14 affected Golden Retrievers in the type 2 study were not homozygous for the common PNPLA1 variant. A negative result for the common type therefore does not exclude another ichthyosis linked to a different gene in the same breed.

Treatment

Treatment also supports the skin barrier

Your vet prescribes treatment and any medication according to your dog's skin changes, disease form and additional problems identified. Regular gentle brushing helps remove loose scales as part of a skin-care plan tailored to the dog.

A suitable mild, emollient shampoo is chosen to reduce scaling without unnecessarily irritating the skin. Emollient skin products support the barrier and help reduce excessive water loss.

Topical products that support the barrier also come as creams, emulsions and leave-on preparations. Good-quality nutrition is maintained, and your vet may assess whether an essential fatty acid supplement should form part of skin care.

Any other identified cause of scaling needs its own treatment, so an inherited diagnosis does not replace investigation of a concurrent skin problem. A superficial secondary bacterial infection is usually treated topically, without automatically prescribing an oral antibiotic.

A deep skin infection is a different situation and usually requires systemic treatment based on bacterial culture and susceptibility testing. When monitoring the response, new itching or new skin changes are reasons to examine the dog again.

An improvement in the skin's appearance means the signs are being controlled: symptomatic treatment does not remove the inherited disorder.

Prevention

Washing or changing the diet of a dog already born cannot prevent an inherited genetic defect, but genetic testing helps inform breeding decisions. When two carriers of a recessive variant are mated, each puppy has a 25% chance of being genetically affected.

A tested carrier can be mated to a dog clear of the same variant, allowing disease prevention to be balanced with preserving the breed's genetic diversity. Some breed-club schemes require a vet or authorised DNA sampler to collect the sample and check the dog's identification before a Golden Retriever's genetic test result can be published.

A clinically normal appearance does not identify all carriers or genetically affected dogs.

Using overly strict restrictions to eliminate a widespread variant can narrow the Golden Retriever breeding population.

Important for dog owners

Record the age when scaling first appeared and photograph the same skin areas during follow-up. As well as checking the abdomen, armpits and flanks, note whether the skin feels painful or has begun to smell. Record itching, licking, pus-filled lesions and changes in your dog's general condition.

Keep the complete genetic test result so that the variant tested and the result classification remain available. Tell your vet about all shampoos, skin products and medicines used, including whether any irritated the skin. Do not start using a human prescription skin medicine on your dog.

Ask for a suitable skin-care plan and practical advice on handling the coat and skin. Monitor how treatment affects comfort, itching and recurring infections, as well as how tidy the coat looks. When planning breeding, check which disease form the parents' tests cover.

Frequently asked questions

Is ichthyosis just ordinary dandruff?

Dandruff is a sign that can result from an allergy, parasite infestation or hormonal disease, for example. In ichthyosis, the cause is an inherited disorder affecting formation of the stratum corneum. Repeated heavy scaling should therefore be investigated before being treated simply as dry skin.

Can a genetically affected dog look healthy?

In Golden Retrievers, a disease-associated genetic result does not always mean continuous, obvious skin signs. Signs may also ease or worsen at different times. A carrier of a recessive condition, meanwhile, is clinically healthy but has a genetic change that can be passed to offspring.

Why does a dog with ichthyosis start itching?

The typical scaling in Golden Retrievers is often non-itchy. A concurrent bacterial or yeast problem can make the skin itchy. New itching is investigated because it may also be associated with allergic skin disease or external parasites. A surface sample helps look for yeast and bacteria on the skin when investigating the cause of itching.

Does a negative genetic test rule out all ichthyosis?

No, because the test targets a named genetic variant. Forms linked to both PNPLA1 and ABHD5 are known in Golden Retrievers. In other breeds, a different gene may underlie the disease, so testing is chosen according to the dog's breed and signs.

Does treatment stop when the coat looks tidy again?

Symptomatic treatment can reduce visible scaling, but it does not correct the inherited keratinisation disorder. The severity of signs can vary throughout life. Ongoing care is tailored to your dog's skin and any infections. Review the plan with the treating vet if the skin becomes irritated or signs return.