Follicular dysplasia in five Weimaraners

Widespread, symmetric, noninflammatory alopecia associated with follicular dysplasia in the American red squirrel (Tamiasciurus hudsonicus)

This report describes a unique pattern of alopecia in 8 American red squirrels (Tamiasciurus hudsonicus) from 2013 to 2021. All animals were juveniles; 6 were female and 2 were male. Seven presented between September and November, and one presented in April. All squirrels had widespread, bilaterally symmetric, noninflammatory, well-demarcated alopecia involving the entire trunk and legs and normal hair on their muzzle and dorsal surfaces of their paws. Six months later, a normal hair coat had grown on 2 of the animals, which were littermates. Hair fully grew 2 months later in another animal. Histopathology of the alopecic skin was performed in 7 of 8 animals. The following changes were noted: bent and coiled hairs, perforating folliculitis, melanin clumping, and distortion of hair shafts. Based on features of follicular dysplasia and apparent seasonality, this condition has some similarities to canine seasonal flank alopecia. A genetic etiology is suspected.

Canine noninflammatory alopecia: An approach to its classification and a diagnostic aid

Noninflammatory alopecia is common in dogs and is a frequent cause to consult a veterinarian. It is also a common reason to take biopsies. Noninflammatory alopecia can be attributed to a decreased formation or cytodifferentiation of the hair follicle or the hair shaft in utero, resulting in congenital alopecia. Congenital alopecia often has a hereditary cause, and examples of such disorders are ectodermal dysplasias associated with gene variants of the ectodysplasin A gene. Noninflammatory alopecia may also be caused by impaired postnatal regeneration of hair follicles or shafts. Such disorders may have a clear breed predilection, and alopecia starts early in life. A hereditary background is suspected in those cases but has not been proven. They are referred to as follicular dysplasia although some of these disorders present histologically like a hair cycle disturbance. Late-onset alopecia is usually acquired and may be associated with endocrinopathies. Other possible causes are impaired vascular perfusion or stress. As the hair follicle has limited possible responses to altered regulation, and histopathology may change during the course of a disease, a detailed clinical history, thorough clinical examination including blood work, appropriate biopsy site selection, and detailed histological findings need to be combined to achieve a final diagnosis. This review aims to provide an overview about the known noninflammatory alopecic disorders in dogs. As the pathogenesis of most disorders is unknown, some statements are based on comparative aspects or reflect the authors' opinion.

Trichographic features of hair from normal black Dobermann pinscher dogs

BACKGROUND

Dobermann dogs are predisposed to colour dilution alopecia and follicular dysplasia. Limited information is available regarding the trichographic features of normal canine hair shafts, including those from Dobermanns, with no studies of inter-observer agreement for canine trichographic features.

OBJECTIVES

To characterize the trichographic features of normal black Dobermann hair shafts evaluating the following variables; gross appearance, primary versus secondary hairs, colour change, tip structure, curling, twisting, bending, cuticle changes (breaks, compression, loss or abnormal overlapping), fractures and variations in hair diameter.

ANIMALS

Twenty client-owned, normal, black Dobermanns of different ages and genders.

METHODS AND MATERIALS

A systemized trichographic evaluation of hair samples from five body locations, which were evaluated independently by two observers, and inter-observer agreement evaluation. Kappa statistics, positive and negative agreement were determined.

RESULTS

Agreement between investigators ranged from 87% to 99% for each examined variable. Kappa statistics showed excellent (0.81-1.00) to substantial agreement (0.61-0.80) for all variables with the exception of moderate agreement (0.41-0.60) for cuticle compressions and variations in hair diameter. A novel finding of a "round hair tip" was made, which was more commonly found on the dorsal head. Colour change to the proximal hair shaft was more common on the thighs and flanks.

CONCLUSIONS AND CLINICAL IMPORTANCE

Trichographic features of 500 hairs collected from 20 normal black Dobermann dogs are described. A previously unreported finding of round hair tips was seen. We describe a systematic approach for evaluating hair shafts that can be applied in future studies for both normal and abnormal Dobermanns, and potentially other dog breeds.

Tracing the origin of 'blue Weimaraner' dogs by molecular genetics

Weimaraner dogs are defined by light brown coat colour termed grey including several shadings ranging from silver and deer to mouse grey. In contrast, the so-called blue Weimaraners (BW) with lightened black-pigmented coat have been proposed to represent spontaneous revertants in the Weimaraner breed. In order to investigate the genetic determinants of the characteristic grey coat colour versus those of BW, known variation in coat colour genes including TYRP1 and MLPH were analysed in a number of grey and blue dogs. Variations at the B locus cause grey coat colour in Weimaraners via two non-functional TYRP1 copies (bb) including the b(s), b(d) and b(c) alleles. In all BW, at least one functional TYRP1 allele (Bb or BB genotype) was identified. Defined microsatellite alleles in TYRP1 intron 4 are linked to this functional B allele in BW. These alleles were also detected in various other dog breeds, but not in grey Weimaraners. The combination of a dominant trait for blue versus grey together with a specific TYRP1 haplotype in BW suggests that blue coat colour is not the result of spontaneous (back-) mutation in grey Weimaraners. This inference is even emphasized by the presence of a unique Y-chomosomal haplotype in a male offspring of the supposed ancestor of the BW population which - according to pedigree information - carries a copy of the original Y chromosome. Thus, molecular genetic analyses of coat colours combined with Y-chromosomal haplotypes allow tracing the origin of atypical dogs in respective canine populations.

Follicular dysplasia of the adult doberman pinscher

This paper presents the case of an adult female, red Doberman pinscher affected by permanent hypotrichosis, limited to the dorsolumbar region and sides of the trunk. The hypotrichosis began at approximately the age of 2 years and progressed slowly with no skin hyperpigmentation. The clinical and histopathological characteristics are of an uncommon form of follicular dysplasia.

Genes affecting coat colour and pattern in domestic dogs: a review

Tremendous progress has been made in identifying genes involved in pigmentation in dogs in the past few years. Comparative genomics has both aided and benefited from these findings. Seven genes that cause specific coat colours and/or patterns in dogs have been identified: melanocortin 1 receptor, tyrosinase related protein 1, agouti signal peptide, melanophilin, SILV (formerly PMEL17), microphthalmia-associated transcription factor and beta-defensin 103. Although not all alleles have been yet identified at each locus, DNA tests are available for many. The identification of these alleles has provided information on interactions in this complex set of genes involved in both pigmentation and neurological development. The review also discusses pleiotropic effects of some coat colour genes as they relate to disease. The alleles found in various breeds have shed light on some potential breed development histories and phylogenetic relationships. The information is of value to dog breeders who have selected for and against specific colours since breed standards and dog showing began in the late 1800s. Because coat colour is such a visible trait, this information will also be a valuable teaching resource.

An overview on congenital alopecia in domestic animals

Alopecia, that is, lack of hair in any quantity, is a frequent complaint of pet owners. Although mostly acquired, rare congenital forms of alopecia exist that are associated with abnormalities in hair follicle morphogenesis. Congenital alopecias can result in changes in quality or quantity of hair follicles and the hair fibres produced by them. They vary in terms of clinical presentation and mode of inheritance. Histopathology is usually needed in order to differentiate between a reduced number of otherwise normal hair follicles and qualitative hair follicle abnormalities. Although our understanding of the molecular mechanisms that drive hair follicle morphogenesis in mice and humans has significantly increased during the last decade, still very little is known about congenital alopecias in domestic animals. Because of their rarity and the general lack of knowledge about their pathophysiology, classification of congenital alopecias in domestic animals is still unsatisfactory. This article reviews hair follicle morphogenesis and its most important molecular mechanisms, and it discusses the various forms of congenital alopecia occurring in domestic animals that have been described in the literature, differentiating between hair follicle aplasia, hair follicle dysplasia (i.e. defects associated with hair follicle development and defects associated with hair shaft formation), and neuroectodermal dysplasias, the latter involving the hair follicle pigmentary system.

Congenital follicular dysplasia in five related coatimundis (Nasua nasua)

We report a congenital follicular dysplasia in five coatis from four different litters of the same parents born between 1996 and 2001. These coatis were born apparently alopecic with the entire body covered by very short dark hairs, with secondary lichenification of the skin, crusting and scaling. The main histopathological feature consisted of premature cornification of the cortical cells of the hair shaft. Cells were already fully cornified below the Adamson's fringe, leading to a disorganized, fragmented and constricted hair shaft. Based on the history of the animals and the nature of the lesions, a genetic defect in hair shaft keratinization was suspected.

Polymorphisms within the canine MLPH gene are associated with dilute coat color in dogs

BACKGROUND

Pinschers and other dogs with coat color dilution show a characteristic pigmentation phenotype. The fur colors are a lighter shade, e.g. silvery grey (blue) instead of black and a sandy color (Isabella fawn) instead of red or brown. In some dogs the coat color dilution is sometimes accompanied by hair loss and recurrent skin inflammation, the so called color dilution alopecia (CDA) or black hair follicular dysplasia (BHFD). In humans and mice a comparable pigmentation phenotype without any documented hair loss is caused by mutations within the melanophilin gene (MLPH).

RESULTS

We sequenced the canine MLPH gene and performed a mutation analysis of the MLPH exons in 6 Doberman Pinschers and 5 German Pinschers. A total of 48 sequence variations was identified within and between the breeds. Three families of dogs showed co-segregation for at least one polymorphism in an MLPH exon and the dilute phenotype. No single polymorphism was identified in the coding sequences or at splice sites that is likely to be causative for the dilute phenotype of all dogs examined. In 18 German Pinschers a mutation in exon 7 (R199H) was consistently associated with the dilute phenotype. However, as this mutation was present in homozygous state in four dogs of other breeds with wildtype pigmentation, it seems unlikely that this mutation is truly causative for coat color dilution. In Doberman Pinschers as well as in Large Munsterlanders with BHFD, a set of single nucleotide polymorphisms (SNPs) around exon 2 was identified that show a highly significant association to the dilute phenotype.

CONCLUSION

This study provides evidence that coat color dilution is caused by one or more mutations within or near the MLPH gene in several dog breeds. The data on polymorphisms that are strongly associated with the dilute phenotype will allow the genetic testing of Pinschers to facilitate the breeding of dogs with defined coat colors and to select against Large Munsterlanders carrying BHFD.