Canine neuropathies: powerful spontaneous models for human hereditary sensory neuropathies.

In humans, hereditary sensory neuropathies (HSN), also known as hereditary sensory and autonomic neuropathies (HSAN), constitute a clinically and genetically heterogeneous group of disorders characterized by progressive sensory loss, often accompanied by chronic skin ulcerations and nail dystrophic changes. To date, although around 20 genes have already been discovered, they do not explain the genetic causes of all patients. In dogs, similar neuropathies are also diagnosed, several breeds being predisposed to specific forms of the disease. Indeed, the breed specificity of most canine genetic diseases is due to the small numbers of founders and high levels of inbreeding. Recent knowledge and tools developed to study the canine genome efficiently allows deciphering the genetic bases of such diseases. To date, a dozen breeds are recognized to develop specific HSN. For the Border collie and hunting dog breeds, the genes involved have recently been discovered. Other affected breeds thus constitute potential genetic models, with new genes to be found in dogs that can be considered as candidate genes for human HSAN/HSN. Here, we review the different forms of human and canine HSAN/HSN and we present a novel form in Fox terrier cases, highlighting the advantages of the dog model for such rare human diseases.

A Point Mutation in a lincRNA Upstream of GDNF Is Associated to a Canine Insensitivity to Pain: A Spontaneous Model for Human Sensory Neuropathies.

Human Hereditary Sensory Autonomic Neuropathies (HSANs) are characterized by insensitivity to pain, sometimes combined with self-mutilation. Strikingly, several sporting dog breeds are particularly affected by such neuropathies. Clinical signs appear in young puppies and consist of acral analgesia, with or without sudden intense licking, biting and severe self-mutilation of the feet, whereas proprioception, motor abilities and spinal reflexes remain intact. Through a Genome Wide Association Study (GWAS) with 24 affected and 30 unaffected sporting dogs using the Canine HD 170K SNP array (Illumina), we identified a 1.8 Mb homozygous locus on canine chromosome 4 (adj. p-val = 2.5x10-6). Targeted high-throughput sequencing of this locus in 4 affected and 4 unaffected dogs identified 478 variants. Only one variant perfectly segregated with the expected recessive inheritance in 300 sporting dogs of known clinical status, while it was never present in 900 unaffected dogs from 130 other breeds. This variant, located 90 kb upstream of the GDNF gene, a highly relevant neurotrophic factor candidate gene, lies in a long intergenic non-coding RNAs (lincRNA), GDNF-AS. Using human comparative genomic analysis, we observed that the canine variant maps onto an enhancer element. Quantitative RT-PCR of dorsal root ganglia RNAs of affected dogs showed a significant decrease of both GDNF mRNA and GDNF-AS expression levels (respectively 60% and 80%), as compared to unaffected dogs. We thus performed gel shift assays (EMSA) that reveal that the canine variant significantly alters the binding of regulatory elements. Altogether, these results allowed the identification in dogs of GDNF as a relevant candidate for human HSAN and insensitivity to pain, but also shed light on the regulation of GDNF transcription. Finally, such results allow proposing these sporting dog breeds as natural models for clinical trials with a double benefit for human and veterinary medicine.

[Spontaneous models of human diseases in dogs: ichthyoses as an example]. / Modèles spontanés de maladies humaines chez le chien: exemple des ichtyoses.

Ichthyoses encompass a heterogeneous group of genodermatoses characterized by abnormal desquamation over the entire body due to defects of the terminal differentiation of keratinocytes and desquamation, which occur in the upper layer of the epidermis. Even though in humans more than 40 genes have already been identified, the genetic causes of several forms remain unknown and are difficult to identify in Humans. Strikingly, several purebred dogs are also affected by specific forms of ichthyoses. In the Golden retriever dog breed, an autosomal recessive form of ichthyosis, resembling human autosomal recessive congenital ichthyoses, has recently been diagnosed with a high incidence. We first characterized the disease occurring in the golden retriever breed and collected cases and controls. A genome-wide association study on 40 unrelated Golden retriever dogs, using the canine 49.000 SNPs (single nucleotide polymorphisms) array (Affymetrix v2), followed by statistical analyses and candidate gene sequencing, allowed to identify the causal mutation in the lipase coding PNPLA1 gene (patatin-like phospholipase domain-containing protein). Screening for alterations in the human ortholog gene in 10 autosomal recessive congenital ichthyoses families, for which no genetic cause has been identified thus far, allowed to identify two recessive mutations in the PNPLA1 protein in two families. This collaborative work between "human" and "canine" geneticists, practicians, histopathologists, biochemists and electron microscopy experts not only allowed to identify, in humans, an eighth gene for autosomal recessive congenital ichthyoses, but also allowed to highlight the function of this as-yet-unknown skin specific lipase in the lipid metabolism of the skin barrier. For veterinary medicine and breeding practices, a genetic test has been developed. These findings illustrate the importance of the discovery of relevant human orthologous canine genetic diseases, whose causes can be tracked in dog breeds more easily than in humans. Indeed, due to the selection and breeding practices applied to purebred dogs, the dog constitutes a unique species for unravelling phenotype/genotype relationships and providing new insights into human genetic diseases. This work paves the way for the identification of rare gene variants in humans that may be responsible for other keratinisation and epidermal barrier defects.

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.

Dermatophytosis due to Microsporum persicolor: a retrospective study of 16 cases.

A retrospective study of 16 cases of dermatophytosis due to Microsporum persicolor in dogs is reported. Hunting dogs were overrepresented (12/16). Skin lesions were observed on the face in all cases, but also on other locations (limbs, neck). The lesions included alopecia (15/16), erythema (13/16), scales (14/16), and crusts (13/16). Histopathology was performed in 10 cases and showed folliculitis and a lichenoid interface dermatitis. Fungal culture was positive in all cases and clinical resolution was achieved with standard antifungal agents (enilconazole, ketoconazole, griseofulvin). Two recurrences were observed (new contacts with rodents).

Metastatic calcinosis (including calcinosis cutis) in a young dog with multiple urinary tract abnormalities.

Metastatic calcinosis associated with chronic renal failure and multiple urinary tract abnormalities was diagnosed in a 6-month-old Brittany spaniel that was presented with calcinosis cutis. This case report highlights the importance of skin as an indicator of systemic disease. The aetiopathogenesis of the four main types of tissue calcification is defined and discussed with an emphasis on metastatic calcinosis.

Sustained phenotypic reversion of junctional epidermolysis bullosa dog keratinocytes: Establishment of an immunocompetent animal model for cutaneous gene therapy.

Gene transfer represents the unique therapeutic issue for a number of inherited skin disorders including junctional epidermolysis bullosa (JEB), an untreatable genodermatose caused by mutations in the adhesion ligand laminin 5 (alpha3beta3gamma2) that is secreted in the extracellular matrix by the epidermal basal keratinocytes. Because gene therapy protocols require validation in animal models, we have phenotypically reverted by oncoretroviral transfer of the curative gene the keratinocytes isolated from dogs with a spontaneous form of JEB associated with a genetic mutation in the alpha3 chain of laminin 5. We show that the transduced dog JEB keratinocytes: (1) display a sustained secretion of laminin 5 in the extracellular matrix; (2) recover the adhesion, proliferation, and clonogenic capacity of wild-type keratinocytes; (3) generate fully differentiated stratified epithelia that after grafting on immunocompromised mice produce phenotypically normal skin and sustain permanent expression of the transgene. We validate an animal model that appears particularly suitable to demonstrate feasibility, efficacy, and safety of genetic therapeutic strategies for cutaneous disorders before undertaking human clinical trials.

Inherited junctional epidermolysis bullosa in the German Pointer: establishment of a large animal model.

Junctional epidermolysis bullosa (JEB) is a genodermatosis suitable for gene therapy because conventional treatments are ineffective. Here, we elucidate the genetic basis of mild JEB in a breed of dogs that display all the clinical traits observed in JEB patients. The condition is associated with reduced expression of laminin 5 caused by a homozygous insertion (4818+207ins6.5 kb) of repetitive satellite DNA within intron 35 of the gene (lama3) for the laminin alpha3 chain. The intronic mutation interferes with maturation of the alpha3 pre-messenger RNA resulting in the coexpression of a transcript with a 227 nucleotide insertion and a wild-type mRNA that encodes scant amounts of the alpha3 polypeptide. Our results show that the amino acid sequence and structure of the canine and human alpha3 chain are highly conserved and that the reduced expression of laminin 5 affects the adhesion and clonogenic potential of the JEB keratinocytes. These JEB dogs provide the opportunity to perform gene delivery in a naturally occurring genodermatosis and to evaluate host tolerance to recombinant laminin 5.

Cyclosporin A: a new drug in the field of canine dermatology.

In the last few years, there has been growing interest in the use of cyclosporin to treat canine skin diseases. Cyclosporin exhibits potent immunomodulating properties that reflect its ability to block the transcription of cytokines genes in activated T lymphocytes. Cyclosporin also inhibits a number of immune allergic reactions that occur after activation of mast cells, Langerhans cells, eosinophils and keratinocytes. In randomized controlled trials, cyclosporin has proven to be as effective as glucocorticoids for treatment of canine atopic dermatitis at the inducing dosage of 5 mg kg(-1). The drug has also proven beneficial for the treatment of perianal fistulas in dogs. Other potential applications are suggested from small pilot open trials using dogs affected with various immune-mediated dermatological diseases. The pharmacokinetic properties of cyclosporin are very similar in dogs and man, but its safety margin is much wider in dogs. Therefore, routine cyclosporin blood level monitoring does not appear necessary. Although in man renal impairment and hypertension are often seen, even at low doses, these effects are not observed in dogs. Adverse reactions consist mainly of transient emesis and diarrhoea occurring during the first days of treatment. Other adverse reactions, such as gingival hyperplasia, verruciform lesions and hypertrichosis, appear to be dose-dependent, and occur rarely at therapeutic doses. An increased susceptibility to infections has not been reported in dogs receiving this drug.

Randomized controlled trial of the efficacy of cyclosporine in the treatment of atopic dermatitis in dogs.

OBJECTIVE: To evaluate efficacy of cyclosporine A, administered at either of 2 dosages, in dogs with atopic dermatitis (AD). DESIGN: Multicenter randomized controlled trial. ANIMALS: 91 dogs with AD. PROCEDURE: Dogs were assigned to receive placebo (30 dogs), cyclosporine at a low dosage (2.5 mg/kg [1.1 mg/lb], PO, q 24 h for 6 weeks; 30 dogs), or cyclosporine at a high dosage (5.0 mg/kg [2.3 mg/lb], PO, q 24 h for 6 weeks; 31 dogs). RESULTS: After 6 weeks, mean percentage reductions, compared with baseline scores, in scores of lesion severity were 34, 41, and 67% for dogs treated with the placebo, cyclosporine at the low dosage, and cyclosporine at the high dosage, respectively. Similarly, mean percentage reductions in pruritus scores were 15, 31, and 45%, respectively. Percentage reductions in skin lesion and pruritus scores were significantly higher for dogs given cyclosporine at the high dosage than for dogs given the placebo. Treatment efficacy was significantly associated with whether dogs had a history of seasonal AD. Percentage reductions in skin lesion and pruritus scores were high for dogs treated with cyclosporine at the highest dosage that had a history of nonseasonal AD. Dogs in all groups with seasonal AD improved during the study period. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that oral administration of cyclosporine at a dosage of 5.0 mg/kg once daily is effective in reducing severity of pruritus and skin lesions in dogs with AD, especially those with nonseasonal disease.

Feline acne and results of treatment with mupirocin in an open clinical trial: 25 cases (1994-96).

Clinical and diagnostic parameters, and response to topical mupirocin in 25 cats with feline acne are described. The chin was the most common area affected, but the lower lip, upper lip and the commissure of the lips also frequently had lesions. The most common clinical sign was the presence of crusts, followed by comedones, erythema, alopecia, pruritus and nodules/fistulas. Deep skin scrapings for ectoparasites, cytological examination of superficial skin scrapings, and fungal cultures from the chin were performed on all cats. Dermatophytes were cultured from two cats and Malassezia pachydermatis was cultured (n = 2), seen on cytology smears (n = 1), or noted on histopathology (n = 1). Skin biopsies were obtained from three of the cats and most commonly showed dilatation of sebaceous gland ducts, neutrophilic or pyogranulomatous infiltration of the sebaceous glands, and pyogranulomatous inflammation of the dermis. All cats were treated with topical 2% mupirocin ointment twice daily for 3 weeks as the sole treatment. Treatment response was excellent in 15 cats and good in nine cats. One cat had a contact reaction to the mupirocin, necessitating stopping treatment. The response to treatment of the six cats with dermatophyte or years involvement was good (n = 3) or excellent (n = 3).

Topical treatment of canine and feline pyoderma.

Abstract This paper is a review of commonly used topical antibacterial medications: benzoyl peroxide, chlorhexidine, povidone iodine, ethyl lactate, triclosan, mupirocin, neomycin, polymyxin B, bacitracin and fusidic acid. Included is a review of the pharmacokinetics, modes of action, adverse effects and clinical uses in veterinary dermatology. General recommendations for topical antibacterial therapy are presented. Résumé- Cet article est une revue des topiques antibactériens les plus couramment utilisés: peroxyde de benzoyle, chlorhexidine, povidone iodée, lactate d'éthyle, triclosan, mupirocine, néomycine, polymyxine B, bacitracine et acide fucidique. Il inclut notamment une revue des pharmacocinétiques, des modes d'action, des effets secondaires et des indications thérapeutiques de ces produits en dermatologie vétérinaire. Les indications générales du traitement topique antibactérien sont présentées. [Guaguere, E. Topical treatment of canine and feline pyoderma. (Traitement topique des pyodermites canines et félines). Veterinary Dermatology 1996; 7: 145-151.] Resumen Este articulo es una revisión de los productos tópicos antibacterianos más frecuentemente utilizados: peróxido de benzoilo, clorhexidina, povidona yodada, etillactato, triclosan, mupirocina, neomicina, polimixina B, bacitracina y ácido fusidico. Se incluye una revisión de la farmacocinética, mecanismos de acción, efectos colaterales y sus usos clínicos en dermatologia veterinaria. Se presentan recomendaciones generales para la terapia antibacteriana tópica. [Guaguere, E. Topical treatment of canine and feline pyoderma. (Tratamiento topico de la pioderma canina y felina). Veterinary Dermatology 1996; 7: 145-151.] Zusammenfassung- Diese Veröffentlichung besteht in einer Übersicht von häufig verwendeten topischen antibakteriellen Arzneimitteln: Benzoylperoxid, Chlorhexidin, Povidon-Jod, Ethyllaktat, Triklosan, Mupirocin, Neomycin, Polymyxin B, Bacitracin und Fusidinsäure. Mit eingeschlossen ist eine Übersicht über Pharmakokinetik, Wirkungsweise, Nebenwirkungen und klinische Anwendung in der Veterinärdermatologie. Allgemeine Empfehlungen für die lokale antibakterielle Therapie werden dargestellt. [Guaguere, E. Topical treatment of canine and feline pyoderma (Lokale Behandlung von kaninen und felinen Pyodermien). Veterinary Dermatology 1996; 7: 145-151.].

Sensitisation to the House Dust Mite, Dermatophagoides farinae, in Dogs with Sarcoptic Mange.

Abstract- Sensitisation to the house dust mite, Dermatophagoides farinae, was demonstrated by skin testing and allergen-specific IgG determination in 15 out of 20 dogs in which a definitive diagnosis of sarcoptic mange was made following recovery of Sarcoptes scabiei mites on skin scrapings. After therapy, no dogs exhibited clinical signs of atopic dermatitis. Intradermal skin testing and 40 per cent of specific IgG assays for Dermatophagoides farinae were negative 90-180 DAys after the original diagnosis. Résumé- Une sensibilisation a l'acarien de la poussière de maison, Dermatophagoides farinae, est demontrée par tests cutanés et dosage d'immunoglobulines IgG specifiques d'allergenes sur 15/20 chiens atteints de gale sarcoptique prouvée par la presence de nombreux sarcoptes aux raclages cutanés. Après traitement, aucun chien n'a présenté des signes cliniques de dermatite atopique. Les tests cutanés intradermiques et 40 plus des posages IgG pour Dermatophagoides farinae sont negatifs 90 à 180 jours après le diagnostic initial. [Prélaud, P., Guaguère, E. Sensitisation to the house dust mite, Dermatophagoides farinae, in dogs with sarcoptic mange (Une sensitisation à l'acarien de la poussière de maison sur les chiens atteints de gale sarcoptique).