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.

Dermatological Problems of Brachycephalic Dogs

Brachycephalic dogs are not only affected by brachycephalic obstructive airway syndrome (BOAS), but are also frequently referred to veterinary dermatologists for skin conditions, with English bulldogs and pugs particularly over-represented. Some skin diseases, such as skin fold dermatitis, are directly associated with the abnormal anatomic conformation of brachycephalic dogs, while for others, such as atopic dermatitis and viral pigmented plaques, there is an underlying genetic basis or a general predisposition. Anatomic alterations associated with brachycephaly, leading to fold formation of the skin and stenosis of the ear canal, together with primary immunodeficiencies described in some breeds, favor the development of pyoderma, Malassezia dermatitis, and otitis externa/media. In addition, the frequently neglected but often lifelong dermatological problems of brachycephalic dogs are an important consideration when discussing genetic and medical conditions affecting the welfare of those dogs. Here we review the current state of knowledge concerning dermatological problems in brachycephalic dogs and combine it with clinical experience in the management of these challenging disorders.

MYO5A Frameshift Variant in a Miniature Dachshund with Coat Color Dilution and Neurological Defects Resembling Human Griscelli Syndrome Type 1

A 1-month-old, female, smooth-haired miniature Dachshund with dilute color and neurological defects was investigated. The aim of this study was to characterize the clinical signs, histopathological changes and underlying genetic defect. The puppy had visible coat color dilution and was unable to hold its head on its own or to remain in a stable prone position for an extended period. Histopathological examination revealed an accumulation of clumped melanin and deposition of accumulated keratin within the hair follicles, accompanied by dermal pigmentary incontinence. These dermatological changes were compatible with the histopathology described in dogs with an MLPH-related dilute coat color. We sequenced the genome of the affected dog and compared the data to 795 control genomes. MYO5A, coding for myosin VA, was investigated as the top functional candidate gene. This search revealed a private homozygous frameshift variant in MYO5A, XM_022412522.1:c.4973_4974insA, predicted to truncate 269 amino acids (13.8%) of the wild type myosin VA protein, XP_022268230.1:p.(Asn1658Lysfs*28). The genotypes of the index family showed the expected co-segregation with the phenotype and the mutant allele was absent from 142 additionally genotyped, unrelated Dachshund dogs. MYO5A loss of function variants cause Griscelli type 1 syndrome in humans, lavender foal in horses and the phenotype of the dilute mouse mutant. Based on the available data, together with current knowledge on other species, we propose the identified MYO5A frameshift insertion as a candidate causative variant for the observed dermatological and neurological signs in the investigated dog.

Towards Forensic DNA Phenotyping for Predicting Visible Traits in Dogs

The popularity of dogs as human companions explains why these pets regularly come into focus in forensic cases such as bite attacks or accidents. Canine evidence, e.g., dog hairs, can also act as a link between the victim and suspect in a crime case due to the close contact between dogs and their owners. In line with human DNA identification, dog individualization from crime scene evidence is mainly based on the analysis of short tandem repeat (STR) markers. However, when the DNA profile does not match a reference, additional information regarding the appearance of the dog may provide substantial intelligence value. Key features of the dog's appearance, such as the body size and coat colour are well-recognizable and easy to describe even to non-dog experts, including most investigating officers and eyewitnesses. Therefore, it is reasonable to complement eyewitnesses' testimonies with externally visible traits predicted from associated canine DNA samples. Here, the feasibility and suitability of canine DNA phenotyping is explored from scratch in the form of a proof of concept study. To predict the overall appearance of an unknown dog from its DNA as accurately as possible, the following six traits were chosen: (1) coat colour, (2) coat pattern, (3) coat structure, (4) body size, (5) ear shape, and (6) tail length. A total of 21 genetic markers known for high predicting values for these traits were selected from previously published datasets, comprising 15 SNPs and six INDELS. Three of them belonged to SINE insertions. The experiments were designed in three phases. In the first two stages, the performance of the markers was tested on DNA samples from dogs with well-documented physical characteristics from different breeds. The final blind test, including dogs with initially withheld appearance information, showed that the majority of the selected markers allowed to develop composite sketches, providing a realistic impression of the tested dogs. We regard this study as the first attempt to evaluate the possibilities and limitations of forensic canine DNA phenotyping.

Differences in melanin type and content among color variations in American mink (Neovison vison)

Coat colour is one of the most important qualitative traits of fur animals. Determining melanin pigments forming the basics of visible coat colour may contribute to a better understanding of the process of creating different coat colour variations in fur-bearing animals. This study aimed to (i) isolate pigment cells from the hair of American mink of 11 colour variations (standard brown, silverblue, palomino, black, wild type, sapphire, black cross, pearl, palomino cross, glow, and amber) using acid and alkali; and (ii) characterise the melanin pigments obtained. The purified pigment cells were observed under a light microscope and verified by spectrophotometry scanning and nuclear magnetic resonance spectroscopy. The method allowed for obtaining pure melanin specimens. Using acid and alkali to extract eumelanosomes did not affect their shape and structure; it also allowed for obtaining pheomelanin from the hair. The results have proven that the hair colour of the American mink is based on all types of melanin, and that its variations differ in terms of how much eumelanin and pheomelanin the hair contains.

Inheritance of different coat colours in Newfoundland dogs in Poland

The aim of the study was to present the manner in which coat colour genes are inherited in the Newfoundland dog breed and to estimate the number of dogs with various coat colours in the Polish Newfoundland dog population in 2017. This population numbered 656 dogs, including 248 males and 408 females. The estimated number of dogs of this breed also included all registered puppies, broken down by gender and coat colour. The genes determining coat colour are described, including more precisely the genes responsible for the coat colour of the Newfoundland breed. According to FCI regulations, the coat colours for Newfoundland dogs are black, brown and black-and-white. Other colours, such as brown-and-white or blue, are not recognized for breeding purposes in Europe. The study found that the dominant black coat was predominant in the Polish Newfoundland dog population in 2017. These dogs could be heterozygous at some other loci and have undesirable alleles. The second most common coat colour was chocolate, while the fewest dogs had spotted coats. The group with spotted coats contained more males than females, in contrast to the other two colour variants. There were also individuals with the blue coat colour, which is not accepted for breeding, as the result of mating of parents with proper coat colours. An understanding of how dog coat colours are inherited and the need for tests to determine coat colour genotypes would make it possible to foresee the occurrence of incorrect colours in subsequent generations, which is crucial for Newfoundland dog breeders, whose goal is to obtain dogs whose coat colour is in line with the FCI standard.

New Insights into the Melanophilin (MLPH) Gene Affecting Coat Color Dilution in Rabbits

Coat color dilution corresponds to a specific pigmentation phenotype that leads to a dilution of wild type pigments. It affects both eumelanin and pheomelanin containing melanosomes. The mode of inheritance of the dilution phenotype is autosomal recessive. Candidate gene approaches focused on the melanophilin (MLPH) gene highlighted two variants associated with the dilution phenotype in rabbits: The c.111-5C>A variant that is located in an acceptor splice site or the c.585delG variant, a frameshift mutation. On the transcript level, the skipping of two exons has been reported as the molecular mechanism responsible for the coat color dilution. To clarify, which of the two variants represents the causal variant, (i) we analyzed their allelic segregation by genotyping Castor and Chinchilla populations, and (ii) we evaluated their functional effects on the stability of MLPH transcripts in skin samples of animals with diluted or wild type coat color. Firstly, we showed that the c.585delG variant showed perfect association with the dilution phenotype in contrast to the intronic c.111-5C>A variant. Secondly, we identified three different MLPH isoforms including the wild type isoform, the exon-skipping isoform and a retained intron isoform. Thirdly, we observed a drastic and significant decrease of MLPH transcript levels in rabbits with a coat color dilution (p-values ranging from 10⁻⁰³ to 10⁻⁰⁶). Together, our results bring new insights into the coat color dilution trait.

A novel MLPH variant in dogs with coat colour dilution

Coat colour dilution may be the result of altered melanosome transport in melanocytes. Loss-of-function variants in the melanophilin gene (MLPH) cause a recessively inherited form of coat colour dilution in many mammalian and avian species including the dog. MLPH corresponds to the D locus in many domestic animals, and recessive alleles at this locus are frequently denoted with d. In this study, we investigated dilute coloured Chow Chows whose coat colour could not be explained by their genotype at the previously known MLPH:c.-22G>A variant. Whole genome sequencing of such a dilute Chow Chow revealed another variant in the MLPH gene: MLPH:c.705G>C. We propose to designate the corresponding mutant alleles at these two variants d¹ and d² . We performed an association study in a cohort of 15 dilute and 28 non-dilute Chow Chows. The dilute dogs were all either compound heterozygous d¹ /d² or homozygous d² /d² , whereas the non-dilute dogs carried at least one wildtype allele D. The d² allele did not occur in 417 dogs from diverse other breeds. However, when we genotyped a Sloughi family, in which a dilute coloured puppy had been born out of non-dilute parents, we again observed perfect co-segregation of the newly discovered d² allele with coat colour dilution. Finally, we identified a blue Thai Ridgeback with the d¹ /d² genotype. Thus, our data identify the MLPH:c.705G>C as a variant explaining a second canine dilution allele. Although relatively rare overall, this d² allele is segregating in at least three dog breeds, Chow Chows, Sloughis and Thai Ridgebacks.

Identification of SNP c.-22G>A in the melanophilin gene from a dog with color dilution alopecia: case report

ABSTRACT Mutant color alopecia is an ectodermical defection of color dilution, characterized by partial alopecia, dry, shine-less hair, and peeling and papule. Melanization damages also occur on the cortical structure of the affected hair. The animals affected have big melanin grains with irregular shape on the basal keratinocytes, also on the hair matrix cells and rod. Therefore, there is not a specific treatment that makes any difference on the syndrome evolution. Although in some animals, it is possible to use weekly showers with benzyl peroxide to reduce seborrhea formation and secondary infections. There is evidence that the condition in dogs is caused by a single nucleotide polymorphism in the gene encoding the melanophilin protein. In the present study the identification of the SNP c.-22G>A in the melanophilin gene of a Dachshund breed dog with clinical and histopathologic evidence of color dilution alopecia is reported.

Genetic testing in veterinary dermatology

BACKGROUND

Molecular genetics has made significant advances in the analysis of hereditary dermatoses during the last several years.

OBJECTIVES

To provide an update on currently available genetic tests for skin diseases of dogs, cats and horses, and to aid the veterinary clinician in the appropriate selection and applications of genetic tests.

METHODS

The scientific literature on the topic was critically reviewed. The list of known causative variants for genodermatoses and hair morphology traits was compiled by searching the Online Mendelian Inheritance in Animals (OMIA) database.

RESULTS

Genetic testing has become an important diagnostic method in veterinary medicine. Genetic tests can help to establish the correct diagnosis in some diseases with relatively nonspecific signs. Genetic tests are also essential for sustainable breeding programmes and to help minimize the frequency of animals with hereditary diseases. Advances in genetic methodology and bioinformatics already allow genome-wide screening for potential disease causing mutations for research purposes. It is anticipated that this will become a routine process in clinical practice in the future.

CONCLUSION AND CLINICAL IMPORTANCE

As specific DNA tests and broad genome-wide analyses come into more common use, it is critical that clinicians understand the proper application and interpretation of these test results.

Epistatic interactions between at least three loci determine the "rat-tail" phenotype in cattle

BACKGROUND

The "rat-tail" syndrome (RTS) is an inherited hypotrichosis in cattle, which is exclusively expressed in diluted coloured hair. The affected animals also suffer from disturbed thermoregulation, which impairs their health and growth performance. Phenotypic features that are similar to RTS are observed in dogs with black hair follicle dysplasia.

RESULTS

We used a resource cross population between German Holstein and Charolais cattle breeds to prove that epistatic interactions between at least three independent genetic loci are required for the expression of the RTS phenotype. In this population, the RTS is exclusively expressed in animals with a eumelanic background that is due to the dominant E (D) allele at the melanocortin 1 receptor gene located on Bos taurus autosome (BTA) 18. In addition, only the individuals that are heterozygous at the dilution locus on BTA5 that corresponds to the premelanosome protein or silver gene variant c.64G>A were classified as displaying a RTS phenotype. Linkage and whole-genome association analyses using different models and different pedigrees allowed us to map a third locus (hereafter referred to as the RTS locus) that is essential for the expression of the RTS phenotype to the chromosomal region between 14 and 22 Mb on BTA5. Our findings clearly demonstrate that the RTS and dilution loci are distinct loci on BTA5.

CONCLUSIONS

Our study provides evidence that the RTS locus has effects on hair conformation and coat colour dilution and that the effect on coat colour dilution is clearly independent from that of the dilution locus. Finally, our results excluded several other loci that were previously reported to be associated with or to underlie hair conformation or pigmentation traits as the causal mutations of RTS and also several major functional candidate genes that are associated with hypotrichosis in humans. Our finding on the identification of a three-locus interaction that underlies RTS provides a prime example of epistatic interaction between several independent loci that is required for the expression of a distinct phenotype.

The lavender plumage colour in Japanese quail is associated with a complex mutation in the region of MLPH that is related to differences in growth, feed consumption and body temperature

Background

The lavender phenotype in quail is a dilution of both eumelanin and phaeomelanin in feathers that produces a blue-grey colour on a wild-type feather pattern background. It has been previously demonstrated by intergeneric hybridization that the lavender mutation in quail is homologous to the same phenotype in chicken, which is caused by a single base-pair change in exon 1 of MLPH.

Results

In this study, we have shown that a mutation of MLPH is also associated with feather colour dilution in quail, but that the mutational event is extremely different. In this species, the lavender phenotype is associated with a non-lethal complex mutation involving three consecutive overlapping chromosomal changes (two inversions and one deletion) that have consequences on the genomic organization of four genes (MLPH and the neighbouring PRLH, RAB17 and LRRFIP1). The deletion of PRLH has no effect on the level of circulating prolactin. Lavender birds have lighter body weight, lower body temperature and increased feed consumption and residual feed intake than wild-type plumage quail, indicating that this complex mutation is affecting the metabolism and the regulation of homeothermy.

Conclusions

An extensive overlapping chromosome rearrangement was associated with a non-pathological Mendelian trait and minor, non deleterious effects in the lavender Japanese quail which is a natural knockout for PRLH.

Colours of domestication

During the last decade, coat colouration in mammals has been investigated in numerous studies. Most of these studies addressing the genetics of coat colouration were on domesticated animals. In contrast to their wild ancestors, domesticated species are often characterized by a huge allelic variability of coat-colour-associated genes. This variability results from artificial selection accepting negative pleiotropic effects linked with certain coat-colour variants. Recent studies demonstrate that this selection for coat-colour phenotypes started at the beginning of domestication. Although to date more than 300 genetic loci and more than 150 identified coat-colour-associated genes have been discovered, which influence pigmentation in various ways, the genetic pathways influencing coat colouration are still only poorly described. On the one hand, similar coat colourations observed in different species can be the product of a few conserved genes. On the other hand, different genes can be responsible for highly similar coat colourations in different individuals of a species or in different species. Therefore, any phenotypic classification of coat colouration blurs underlying differences in the genetic basis of colour variants. In this review we focus on (i) the underlying causes that have resulted in the observed increase of colour variation in domesticated animals compared to their wild ancestors, and (ii) the current state of knowledge with regard to the molecular mechanisms of colouration, with a special emphasis on when and where the different coat-colour-associated genes act.

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.