Clinical, histopathological and genetic data of ichthyosis in the golden retriever: a prospective study

Inheritance of Monogenic Hereditary Skin Disease and Related Canine Breeds

The plasticity of the genome is an evolutionary factor in all animal species, including canines, but it can also be the origin of diseases caused by hereditary genetic mutation. Genetic changes, or mutations, that give rise to a pathology in most cases result from recessive alleles that are normally found with minority allelic frequency. The use of genetic improvement increases the consanguinity within canine breeds and, on many occasions, also increases the frequency of these recessive alleles, increasing the prevalence of these pathologies. This prevalence has been known for a long time, but mutations differ according to the canine breed. These genetic diseases, including skin diseases, or genodermatosis, which is narrowly defined as monogenic hereditary dermatosis. In this review, we focus on genodermatosis sensu estricto, i.e., monogenic, and hereditary dermatosis, in addition to the clinical features, diagnosis, pathogeny, and treatment. Specifically, this review analyzes epidermolytic and non-epidermolytic ichthyosis, junctional epidermolysis bullosa, nasal parakeratosis, mucinosis, dermoid sinus, among others, in canine breeds, such as Golden Retriever, German Pointer, Australian Shepherd, American Bulldog, Great Dane, Jack Russell Terrier, Labrador Retriever, Shar-Pei, and Rhodesian Ridgeback.

Isotretinoin Treatment for Autosomal Recessive Congenital Ichthyosis in a Golden Retriever

Ichthyoses are hereditary cornification disorders that manifest with abnormal differentiation and desquamation of keratinocytes in a form of generalized dry and scaly skin. In golden retriever dogs, autosomal recessive congenital ichthyosis (ARCI) has been associated with mutations in the PNPLA 1 gene. In human medicine, isotretinoin is frequently used to treat ARCIs. The aim of this study was to investigate the clinical and histological effects of isotretinoin on ARCI in a golden retriever dog with confirmed mutation in the PNPLA 1 gene. Clinical examination, blood analysis and histopathological examinations were conducted before and after 90 days of isotretinoin therapy. The clinical and histopathological findings indicate that treatment with oral isotretinoin was effective in improving ichthyosis without any side-effects.

ABHD5 frameshift deletion in Golden Retrievers with ichthyosis

Ichthyoses are hereditary skin disorders characterized by the formation of scales and defects in the outermost layer of the epidermis. In dogs, at least six different breed-specific ichthyoses including a relatively common PNPLA1-related autosomal recessive ichthyosis in Golden Retrievers are known. In this study, we investigated 14 Golden Retrievers with scales that were not homozygous for the mutant PNPLA1 allele suggesting a genetically distinct new form of ichthyosis. Histopathological examinations showed lamellar, orthokeratotic hyperkeratosis, and mildly hyperplastic epidermis that led to the diagnosis of a nonepidermolytic ichthyosis. Combined linkage and homozygosity mapping in 14 cases and 30 nonaffected family members delimited a critical interval of ∼12.7 Mb on chromosome 23. Whole-genome sequencing of an affected dog revealed a single protein-changing variant within this region that was not present in 795 control genomes. The identified variant is a 14 bp deletion in the ABHD5 gene (c.1006_1019del), leading to a frameshift and altering the last 14 codons p.(Asp336Serfs*6). The genotypes at this variant showed perfect cosegregation with the ichthyosis phenotype in a large family comprising 14 cases and 72 controls. ABHD5 encodes an acyltransferase required for lipid metabolism. In humans, variants in ABHD5 cause Chanarin-Dorfman syndrome, a neutral lipid storage disease with ichthyosis. Our data in dogs together with the knowledge on the effects of ABHD5 variants in humans strongly suggest ABHD5:c.1006_1019del as candidate causative genetic variant for a new canine form of ichthyosis, which we propose to designate as Golden Retriever ichthyosis type 2 (ICH2).

Genes of Congenital Dermatologic Disorders in Dogs—A Review

This article presents an overview of up-to-date identified genes responsible for congenital canine skin diseases of dogs and the characteristics of these diseases. Congenital skin diseases constitute a specific group of dermatologic disorders that plays an important role in breeding of purebred dogs. They include primary seborrhoea, ichthyosis, hereditary nasal parakeratosis, dermatomyositis, colour dilution alopecia, skin mucinosis, dermoid sinus, lethal acrodermatitis, acral mutilation syndrome, keratoconjunctivitis sicca, ichthyosiform dermatosis, bullous epidermolysis, exfoliative dermal lupus erythematosus, congenital footpad hyperkeratosis and sebaceous adenitis. In the majority of cases, their occurrence is linked to particular breeds. In more than half of these diseases a specific defective gene variant responsible for the disease has been identified. Genetic tests for identification of the relevant defective genes serve as an important tool in the diagnostics of diseases in veterinary practice and in breeding of purebred dogs.

Ichthyosis in Dogs—Congenital Dermatologic Disorder

The skin provides protective functions, such as thermoregulation, resorption, provision of immune responses, storage and sensory functions, which all play an important role in the internal stability of the organism. The skin has 3 major layers: the epidermis, the dermis and subcutis. The outermost protective layer of the epidermis, the stratum corneum, consists of 20 to 30 overlapping layers of anucleate cells, the corneocytes. Ichthyosis is an autosomal recessive congenital skin disease, in which the corneocytes form defects that appear like individual steps of the stratum corneum. Ichthyosis is characterized by excessive scaling over the entire body surface and is not curable; the symptoms can only be alleviated. Several genetic variants have been identified in specific dog breeds: PNPLA1 in the Golden Retrievers, SLC27A4 in the Great Danes, NIPAL4 in the American Bulldogs, TGM1 in the Jack Russel Terriers, ASPRV1 in the German Shepherds, which cause different forms of nonepidermolytic ichthyosis and KRT10 in the Norfolk Terriers, which causes epidermolytic ichthyosis. When classifying breeds of dogs predisposed to ichthyosis, it is necessary to determine the presence of defective genes in the genome of the individual animals involved in mating.

Feline maculopapular cutaneous mastocytosis: a retrospective study of 13 cases and proposal for a new classification

CASE SERIES SUMMARY

Cutaneous mastocytosis is a disorder rarely reported in veterinary dermatology and usually described as 'urticaria pigmentosa'. This study aimed to evaluate the diagnosis, treatment and outcome of 13 affected cats, selected from the files of a private referral dermatology practice within a period of 14 years. Breeds of the affected individuals included Sphynx (n = 9), Devon Rex (n = 2) and Sphynx/Devon Rex crossbreeds (n = 2). Females (n = 9) were over-represented and the median duration of clinical signs prior to diagnosis was 8 months. The clinical presentation of these 13 cats was compared with cases reported in the veterinary literature and classified according to the current human consensus on cutaneous mastocytosis. Three clinical forms could be distinguished in cats: (1) large papular lesions and wheals, typically localised to the head, shoulders, ventral neck and axillae, and which may spontaneously resolve (termed polymorphic maculopapular cutaneous mastocytosis); (2) erythematous dermatitis, characterised by small maculopapular lesions often associated with crusts and with a poorer prognosis (termed monomorphic maculopapular cutaneous mastocytosis); and (3) more chronic dermatitis characterised by lichenification and hyperpigmentation, similar to the human condition 'urticaria pigmentosa' (termed pigmented maculopapular cutaneous mastocytosis). Histopathology was performed in eight cases and revealed a superficial-to-deep dermatitis characterised by infiltrates of mast cells and eosinophils. The response to various treatments, including antihistamines, steroids and ciclosporin, was variable.

RELEVANCE AND NOVEL INFORMATION

This article reports 13 new cases of feline cutaneous mastocytosis, confirming the clinical presentation and apparent breed predisposition. The feline maculopapular cutaneous mastocytosis seems to be clinically very close to the human form. This study proposes a new classification system for the feline disease based on the current human consensus, clinical presentation and prognosis, with three different subforms: polymorphic maculopapular cutaneous mastocytosis with eventual spontaneous regression; monomorphic maculopapular cutaneous mastocytosis with chronic evolution; and pigmented maculopapular cutaneous mastocytosis.

Topical polyhydroxy acid treatment for autosomal recessive congenital ichthyosis in the golden retriever: a prospective pilot study

BACKGROUND

Autosomal recessive congenital ichthyosis (ARCI) in golden retrievers is due to a PNPLA1 gene mutation, which plays a role in epidermal lipid organization and metabolism. Topical therapies are used to reduce scaling; however, there are few published efficacy studies.

OBJECTIVES

To examine the efficacy of topical treatment based on gluconolactone, a polyhydroxy acid with known beneficial effects on stratum corneum structure.

ANIMALS

Sixteen golden retriever dogs with clinical signs of ARCI and PCR-confirmed PNPLA1 gene mutation.

METHODS

This was a prospective, multicentre, noncontrolled study. Dogs were treated with a shampoo and lotion containing gluconolactone and other hydroxyl acids. Treatments were administered initially twice weekly for two weeks, then once weekly for two weeks and finally once monthly. Examinations were performed prior to and at 14 and 30 days of treatment to assess scaling, presence of other skin lesions and pruritus. In two dogs, pre- and 30 day post-treatment, skin biopsies were obtained.

RESULTS

The extent and size of the scales were reduced by 60% and 75% after 14 and 30 days of treatment, respectively (P < 0.001). In 20% of the dogs, scaling was no longer observed after the first 30 days of treatment. No other skin lesions or pruritus were observed in any dog. Post-treatment biopsies showed normalization of the stratum corneum morphology and reduced hyperpigmentation.

CONCLUSION AND CLINICAL IMPORTANCE

The frequent use of a shampoo and lotion containing gluconolactone may be an effective measure to improve skin scaling in golden retrievers with ARCI.

Prevalence of PNPLA1 Gene Mutation in 48 Breeding Golden Retriever Dogs

A non-epidermolytic ichthyosis has been identified in Golden Retrievers due to a variant in the PNPLA1 gene, and a genetic test is available to detect wild-type, heterozygous and homozygous dogs. The aims of this study were to investigate the prevalence of the PNPLA1 gene variant in Golden Retrievers used for breeding and to provide more information to breeders in order to restrict the spread of this disease. Clinical examination and assessment of the PNPLA1 genotype using PCR testing of oral swabs were performed in 48 breeding Golden Retrievers. Wild-type, heterozygous or homozygous variants of the PNPLA1 gene were demonstrated in 10 (21%), 23 (48%), and 15 (31%) of the 48 dogs, respectively. In only 3 of the 48 dogs were clinical signs suggestive of ichthyosis identified. Data collected agreed with data reported in the literature. The high prevalence of homozygous and heterozygous variants makes the exclusion of mutated dogs from breeding impractical. Furthermore, the reliability of the PNPLA1 mutation in prediction of clinical signs of ichthyosis is unclear. Additional studies are needed to investigate if PNPLA1 is the only gene involved or if other genes and environmental factors have a role in the development of ichthyosis in Golden Retrievers.

Congenital Ichthyosis in 14 Great Dane Puppies With a New Presentation

The present study describes a generalized congenital skin condition in 14 Great Dane puppies. Macroscopically, all dogs showed generalized gray to yellow scaling and skin wrinkles on the head and all 4 extremities. Skin sections were histologically examined using hematoxylin and eosin, Heidenhain's Azan, and Sudan red III staining methods and by conducting the alcian blue/periodic acid Schiff (AB/PAS) reaction technique on sections. Furthermore, incubation with hyaluronidase was performed. Skin samples were ultrastructurally analyzed using transmission electron microscopy. All affected Great Dane puppies had epidermal and follicular orthokeratotic hyperkeratosis, enlarged keratohyaline granules, vacuolated keratinocytes, and accumulations of an eosinophilic and alcianophilic, lipid-rich material within dilated hair follicular lumina and the cytoplasm of sebocytes. The macroscopic, histopathologic, and ultrastructural skin changes in all 14 Great Dane puppies indicate a new variant of a primary disorder of cornification with congenital, non-epidermolytic, lamellar ichthyosiform appearance.

Is "milk crust" a transient form of golden retriever ichthyosis?

BACKGROUND

A recessive inherited form of lamellar ichthyosis is well recognized in golden retrievers. In this breed, young puppies demonstrate a self-limiting scaling disorder which is commonly recognized by breeders, who use the term "milk crust" to describe this syndrome.

HYPOTHESIS/OBJECTIVES

To determine whether "milk crust" is a new keratinization disorder or a self-limiting form of golden retriever ichthyosis.

ANIMALS

A total of 179 golden retriever dogs (21 dams and 158 puppies) were examined.

METHODS

Dermatological examination and assessment of the patatin-like phospholipase-1 (PNPLA1) genotype by PCR testing of buccal mucosal swabs. Skin biopsies from one affected puppy were evaluated for histopathological abnormalities.

RESULTS

Forty-five of 158 (28%) puppies exhibited scaling at 8 weeks of age; 113 of 158 (72%) were dermatologically normal. Of 144 analysed samples, 40 of 144 (28%) puppies demonstrated a homozygous mutation of the PNPLA1 genotype [of which, 36 of 40 (90%) had signs of scaling], 77 of 144 (53%) demonstrated a heterozygous mutation and 27 of 144 (19%) were a normal wild-type. In six of 17 (35%) dams, a homozygous mutation of the PNPLA1 genotype was found, eight of 17 (47%) demonstrated a heterozygous mutation and three of 17 (18%) were normal wild-type. Dams with a homozygous mutation were clinically unaffected. A 1 year follow-up revealed that 23 of 28 (82%) puppies affected with this syndrome failed to develop typical signs of ichthyosis. In five of 28 (18%) dogs there was persistence of mild scaling.

CONCLUSIONS AND CLINICAL IMPORTANCE

We hypothesize that the clinical syndrome termed "milk crust" could represent a transient form of golden retriever ichthyosis. Remission is not fully linked to PNPLA1 genotype, suggesting that unknown factors may contribute to the clinical disease.

Autosomal Recessive Congenital Ichthyosis in American Bulldogs Is Associated With NIPAL4 (ICHTHYIN) Deficiency

A minority of patients with nonsyndromic autosomal recessive congenital ichthyosis (ARCI) display mutations in NIPAL4 (ICHTHYIN). This protein plays a role in epidermal lipid metabolism, although the mechanism is unknown. The study describes a moderate form of ARCI in an extended pedigree of American Bulldogs that is linked to the gene encoding ichthyin. The gross phenotype was manifest as a disheveled pelage shortly after birth, generalized scaling, and adherent brown scale with erythema of the abdominal skin. Pedigree analysis indicated an autosomal recessive mode of inheritance. Ultrastructurally, the epidermis showed discontinuous lipid bilayers, unprocessed lipid within corneocytes, and abnormal lamellar bodies. Linkage analysis, performed by choosing simple sequence repeat markers and single-nucleotide polymorphisms near genes known to cause ACRI, revealed an association with NIPAL4. NIPAL4 was identified and sequenced using standard methods. No mutation was identified within the gene, but affected dogs had a SINE element 5' upstream of exon 1 in a highly conserved region. Of 545 DNA samples from American Bulldogs, 32 dogs (17 females, 15 males) were homozygous for the polymerase chain reaction fragment. All affected dogs were homozygous, with parents heterozygous for the insertion. Immunolabeling revealed an absence of ichthyin in the epidermis. This is the first description of ARCI associated with decreased expression of NIPAL4 in nonhuman species.

PNPLA1 mutations cause autosomal recessive congenital ichthyosis in golden retriever dogs and humans

Ichthyoses comprise a heterogeneous group of genodermatoses characterized by abnormal desquamation over the whole body, for which the genetic causes of several human forms remain unknown. We used a spontaneous dog model in the golden retriever breed, which is affected by a lamellar ichthyosis resembling human autosomal recessive congenital ichthyoses (ARCI), to carry out a genome-wide association study. We identified a homozygous insertion-deletion (indel) mutation in PNPLA1 that leads to a premature stop codon in all affected golden retriever dogs. We subsequently found one missense and one nonsense mutation in the catalytic domain of human PNPLA1 in six individuals with ARCI from two families. Further experiments highlighted the importance of PNPLA1 in the formation of the epidermal lipid barrier. This study identifies a new gene involved in human ichthyoses and provides insights into the localization and function of this yet uncharacterized member of the PNPLA protein family.