Autosomal recessive hyposegmentation of granulocytes in Australian Shepherd Dogs indicates a role for LMBR1L in myeloid leukocytes.

Pelger-Huët anomaly (PHA) in humans is an autosomal dominant hematological phenotype without major clinical consequences. PHA involves a characteristic hyposegmentation of granulocytes (HG). Human PHA is caused by heterozygous loss of function variants in the LBR gene encoding lamin receptor B. Bi-allelic variants and complete deficiency of LBR cause the much more severe Greenberg skeletal dysplasia which is lethal in utero and characterized by massive skeletal malformation and gross fetal hydrops. HG phenotypes have also been described in domestic animals and homology to human PHA has been claimed in the literature. We studied a litter of Australian Shepherd Dogs with four stillborn puppies in which both parents had an HG phenotype. Linkage analysis excluded LBR as responsible gene for the stillborn puppies. We then investigated the HG phenotype in Australian Shepherd Dogs independently of the prenatal lethality. Genome-wide association mapped the HG locus to chromosome 27 and established an autosomal recessive mode of inheritance. Whole genome sequencing identified a splice site variant in LMBR1L, c.191+1G>A, as most likely causal variant for the HG phenotype. The mutant allele abrogates the expression of the longer X2 isoform but does not affect transcripts encoding the shorter X1 isoform of the LMBR1L protein. The homozygous mutant LMBR1L genotype associated with HG is common in Australian Shepherd Dogs and was found in 39 of 300 genotyped dogs (13%). Our results point to a previously unsuspected function of LMBR1L in the myeloid lineage of leukocytes.

Single-cell profiling of bronchoalveolar cells reveals a Th17 signature in neutrophilic severe equine asthma.

Severe equine asthma (SEA) is a complex respiratory condition characterized by chronic airway inflammation. It shares many clinical and pathological features with human neutrophilic asthma, making it a valuable model for studying this condition. However, the immune mechanisms driving SEA have remained elusive. Although SEA has been primarily associated with a Th2 response, there have also been reports of Th1, Th17, or mixed-mediated responses. To uncover the elusive immune mechanisms driving SEA, we performed single-cell mRNA sequencing (scRNA-seq) on cryopreserved bronchoalveolar cells from 11 Warmblood horses, 5 controls and 6 with SEA. We identified six major cell types, including B cells, T cells, monocytes-macrophages, dendritic cells, neutrophils, and mast cells. All cell types exhibited significant heterogeneity, with previously identified and novel cell subtypes. Notably, we observed monocyte-lymphocyte complexes and detected a robust Th17 signature in SEA, with CXCL13 upregulation in intermediate monocytes. Asthmatic horses exhibited expansion of the B-cell population, Th17 polarization of the T-cell populations, and dysregulation of genes associated with T-cell function. Neutrophils demonstrated enhanced migratory capacity and heightened aptitude for neutrophil extracellular trap formation. These findings provide compelling evidence for a predominant Th17 immune response in neutrophilic SEA, driven by dysregulation of monocyte and T-cell genes. The dysregulated genes identified through scRNA-seq have potential as biomarkers and therapeutic targets for SEA and provide insights into human neutrophilic asthma.

Online Mendelian Inheritance in Animals (OMIA): a genetic resource for vertebrate animals.

Online Mendelian Inheritance in Animals (OMIA) is a freely available curated knowledgebase that contains information and facilitates research on inherited traits and diseases in animals. For the past 29 years, OMIA has been used by animal geneticists, breeders, and veterinarians worldwide as a definitive source of information. Recent increases in curation capacity and funding for software engineering support have resulted in software upgrades and commencement of several initiatives, which include the enhancement of variant information and links to human data resources, and the introduction of ontology-based breed information and categories. We provide an overview of current information and recent enhancements to OMIA and discuss how we are expanding the integration of OMIA into other resources and databases via the use of ontologies and the adaptation of tools used in human genetics.

PCYT2 deficiency in Saarlooswolfdogs with progressive retinal, central, and peripheral neurodegeneration.

We investigated a syndromic disease comprising blindness and neurodegeneration in 11 Saarlooswolfdogs. Clinical signs involved early adult onset retinal degeneration and adult-onset neurological deficits including gait abnormalities, hind limb weakness, tremors, ataxia, cognitive decline and behavioral changes such as aggression towards the owner. Histopathology in one affected dog demonstrated cataract, retinal degeneration, central and peripheral axonal degeneration, and severe astroglial hypertrophy and hyperplasia in the central nervous system. Pedigrees indicated autosomal recessive inheritance. We mapped the suspected genetic defect to a 15 Mb critical interval by combined linkage and autozygosity analysis. Whole genome sequencing revealed a private homozygous missense variant, PCYT2:c.4A>G, predicted to change the second amino acid of the encoded ethanolamine-phosphate cytidylyltransferase 2, XP_038402224.1:(p.Ile2Val). Genotyping of additional Saarlooswolfdogs confirmed the homozygous genotype in all eleven affected dogs and demonstrated an allele frequency of 9.9% in the population. This experiment also identified three additional homozygous mutant young dogs without overt clinical signs. Subsequent examination of one of these dogs revealed early-stage progressive retinal atrophy (PRA) and expansion of subarachnoid CSF spaces in MRI. Dogs homozygous for the pathogenic variant showed ether lipid accumulation, confirming a functional PCYT2 deficiency. The clinical and metabolic phenotype in affected dogs shows some parallels with human patients, in whom PCYT2 variants lead to a rare form of spastic paraplegia or axonal motor and sensory polyneuropathy. Our results demonstrate that PCYT2:c.4A>G in dogs cause PCYT2 deficiency. This canine model with histopathologically documented retinal, central, and peripheral neurodegeneration further deepens the knowledge of PCYT2 deficiency.

Biallelic variants in DNA2 cause poikiloderma with congenital cataracts and severe growth failure reminiscent of Rothmund-Thomson syndrome.

Rothmund-Thomson syndrome (RTS) is a rare, heterogeneous autosomal recessive genodermatosis, with poikiloderma as its hallmark. It is classified into two types: type I, with biallelic variants in ANAPC1 and juvenile cataracts, and type II, with biallelic variants in RECQL4, increased cancer risk and no cataracts. We report on six Brazilian probands and two siblings of Swiss/Portuguese ancestry presenting with severe short stature, widespread poikiloderma and congenital ocular anomalies. Genomic and functional analysis revealed compound heterozygosis for a deep intronic splicing variant in trans with loss of function variants in DNA2, with reduction of the protein levels and impaired DNA double-strand break repair. The intronic variant is shared by all patients, as well as the Portuguese father of the European siblings, indicating a probable founder effect. Biallelic variants in DNA2 were previously associated with microcephalic osteodysplastic primordial dwarfism. Although the individuals reported here present a similar growth pattern, the presence of poikiloderma and ocular anomalies is unique. Thus, we have broadened the phenotypical spectrum of DNA2 mutations, incorporating clinical characteristics of RTS. Although a clear genotype-phenotype correlation cannot be definitively established at this moment, we speculate that the residual activity of the splicing variant allele could be responsible for the distinct manifestations of DNA2-related syndromes.

Heterozygous DSP in-frame deletion in a poodle with syndromic ichthyosis involving additional hair and tooth abnormalities.

Ichthyoses comprise a large heterogeneous group of skin disorders, characterized by generalized scaly and hyperkeratotic skin. We investigated a miniature poodle with early onset generalized scaling, dry and irregularly thickened skin, paw pad hyperkeratosis and abnormalities in hair and teeth. The clinical signs of ichthyosis were confirmed by histopathological examination, which revealed mild epidermal hyperplasia and lamellar orthokeratotic hyperkeratosis. A hereditary condition was suspected and a genetic investigation was initiated. We sequenced the whole genome of the affected dog and searched for potentially causative variants in functional candidate genes for the observed phenotype. The analysis revealed a heterozygous in-frame deletion in DSP, NC_049256.1:g.8804542_8804544del resulting from a de novo mutation event as evidenced by genotyping leukocyte DNA from both parents. The 3 bp deletion is predicted to remove one aspartic acid without disrupting the open reading frame (XM_038584124.1:c.1821_1823del, XP_038440052.1:p.(Asp608del)). The DSP gene encodes desmoplakin, a desmosomal plaque protein, responsible for cell-cell adhesion to provide resistance to mechanical stress in epidermal and cardiac tissues. We hypothesize that the deletion of one amino acid in the N-terminal globular head domain acts in a dominant negative manner and thus impairs the proper connection with other proteins. Several variants in DSP in humans and cattle have been described to result in different phenotypes associated with hair and skin abnormalities, sometimes in combination with variable cardiac and/or dental manifestations. In conclusion, we characterized a new syndromic ichthyosis phenotype in a dog and identified a de novo 3 bp deletion in the DSP gene as causal variant.

KRT5 in-frame deletion in a family of German Shepherd dogs with split paw pad disease resembling localized epidermolysis bullosa simplex in human patients.

Split paw pad disease is a scarcely defined phenotype characterized by skin lesions on the paw pads of dogs. We studied a family of German Shepherd dogs, in which four dogs developed intermittent paw pad lesions and lameness. The paw pads of two of the affected dogs were biopsied and demonstrated cleft formation in the stratum spinosum and stratum corneum, the outermost layers of the epidermis. Whole genome sequencing data from an affected dog revealed a private heterozygous 18 bp in frame deletion in the KRT5 gene. The deletion NM_001346035.1:c.988_1005del or NP_001332964.1:p.(Asn330_Asp335del) is predicted to lead to a loss of six amino acids in the L12 linker domain of the encoded keratin 5. KRT5 variants in human patients lead to various subtypes of epidermolysis bullosa simplex (EBS). Localized EBS is the mildest of the KRT5-related human diseases and may be caused by variants affecting the L12 linker domain of keratin 5. We therefore think that the detected KRT5 deletion in dogs represents a candidate causal variant for the observed skin lesions in dogs. However, while the clinical phenotype of KRT5-mutant dogs of this study closely resembles human patients with localized EBS, there are differences in the histopathology. EBS is defined by cleft formation within the basal layer of the epidermis while the cleft formation in the dogs described herein occurred in the outermost layers, a hallmark of split paw pad disease. Our study provides a basis for further studies into the exact relation of split paw pad disease and EBS.

Intragenic MFSD8 duplication and histopathological findings in a rabbit with neuronal ceroid lipofuscinosis.

Neuronal ceroid lipofuscinoses (NCL) are among the most prevalent neurodegenerative disorders of early life in humans. Disease-causing variants have been described for 13 different NCL genes. In this study, a refined pathological characterization of a female rabbit with progressive neurological signs reminiscent of NCL was performed. Cytoplasmic pigment present in neurons was weakly positive with Sudan black B and autofluorescent. Immunohistology revealed astrogliosis, microgliosis and axonal degeneration. During the subsequent genetic investigation, the genome of the affected rabbit was sequenced and examined for private variants in NCL candidate genes. The analysis revealed a homozygous ~10.7 kb genomic duplication on chromosome 15 comprising parts of the MFSD8 gene, NC_013683.1:g.103,727,963_103,738,667dup. The duplication harbors two internal protein coding exons and is predicted to introduce a premature stop codon into the transcript, truncating ~50% of the wild-type MFSD8 open reading frame encoding the major facilitator superfamily domain containing protein 8, XP_002717309.2:p.(Glu235Leufs*23). Biallelic loss-of-function variants in MFSD8 have been described to cause NCL7 in human patients, dogs and a single cat. The available clinical and pathological data, together with current knowledge about MFSD8 variants and their functional impact in other species, point to the MFSD8 duplication as a likely causative defect for the observed phenotype in the affected rabbit.

Deletion of the SELENOP gene leads to CNS atrophy with cerebellar ataxia in dogs.

We investigated a hereditary cerebellar ataxia in Belgian Shepherd dogs. Affected dogs developed uncoordinated movements and intention tremor at two weeks of age. The severity of clinical signs was highly variable. Histopathology demonstrated atrophy of the CNS, particularly in the cerebellum. Combined linkage and homozygosity mapping in a family with four affected puppies delineated a 52 Mb critical interval. The comparison of whole genome sequence data of one affected dog to 735 control genomes revealed a private homozygous structural variant in the critical interval, Chr4:66,946,539_66,963,863del17,325. This deletion includes the entire protein coding sequence of SELENOP and is predicted to result in complete absence of the encoded selenoprotein P required for selenium transport into the CNS. Genotypes at the deletion showed the expected co-segregation with the phenotype in the investigated family. Total selenium levels in the blood of homozygous mutant puppies of the investigated litter were reduced to about 30% of the value of a homozygous wildtype littermate. Genotyping >600 Belgian Shepherd dogs revealed an additional homozygous mutant dog. This dog also suffered from pronounced ataxia, but reached an age of 10 years. Selenop-/- knock-out mice were reported to develop ataxia, but their histopathological changes were less severe than in the investigated dogs. Our results demonstrate that deletion of the SELENOP gene in dogs cause a defect in selenium transport associated with CNS atrophy and cerebellar ataxia (CACA). The affected dogs represent a valuable spontaneous animal model to gain further insights into the pathophysiological consequences of CNS selenium deficiency.

Skin barrier, phenotypic and genotypic characterisation of autosomal recessive ichthyosis in TGM1-deficient Jack Russell Terriers and response to topical ceramide.

BACKGROUND: Autosomal recessive ichthyosis leads to structural or biochemical changes that impair skin barrier function. HYPOTHESIS/OBJECTIVES: To assess (1) the phenotype and genotype in a litter of Jack Russell Terriers with autosomal recessive congenital ichthyosis (ARCI), and (2) the defective skin barrier and determine if a topical ceramide can modulate the barrier. ANIMALS: A healthy dam and litter of Jack Russell Terrier puppies (healthy male, affected male and female), one affected adult Jack Russell Terrier and one unrelated healthy Jack Russell Terrier. MATERIALS AND METHODS: A severe cornification defect was identified via examination of affected puppies. As the phenotype worsened, the affected puppies received a topical application of ω-0-acylceramide for 10 days. Before humane euthanasia, the skin barrier was evaluated via transepidermal water loss (TEWL), corneometry and pH in affected dogs. Genomic testing was performed, and skin samples were analysed by light and electron microscopy. RESULTS: Affected puppies were homozygous for the 1980 bp LINE-1 insertion in the TGM1 (transglutaminase 1) gene; the unaffected littermate and the dam were heterozygous carriers. ARCI puppies were underweight and had a severe hyperkeratotic phenotype that impaired mobility. TEWL was markedly higher in affected dogs. The cutaneous pH of affected puppies was higher than the normal littermate. Treatment of the skin with ω-0-acylceramide normalised the pH to match the littermate and decreased TEWL. Electron microscopy revealed marked attenuation of the cornified envelope. CONCLUSIONS AND CLINICAL RELEVANCE: Dogs with TGM1-deficient ARCI have an impaired skin barrier. Topical therapy can partially repair the barrier defect.

Novel MRI and histopathological findings in a young Bullmastiff cross dog with mitochondrial fission encephalopathy.

A 9-month-old male Bullmastiff cross dog was presented with a history of progressive proprioceptive ataxia and behavior changes. Neuroanatomical localization was multifocal with forebrain and vestibulo-cerebellum involvement. MRI identified moderate diffuse cerebral sulci widening, dilation of the ventricular system, and rounded, well-defined, bilaterally symmetrical T2W, FLAIR, and T2* hyperintense intra-axial lesions affecting the olivary nuclei. Histopathological examination was indicative of a primary mitochondrial disorder. This was confirmed following genetic analysis which identified mitochondrial fission encephalopathy with a homozygous frameshift variant in the MFF gene. This case report documents diagnostic imaging and histopathological findings not previously reported in dogs affected with mitochondrial fission encephalopathy, suggesting a different selective regional vulnerability of the neurons.

Genetic Variants Affecting Skeletal Morphology in Domestic Dogs.

Purebred dog breeds provide a powerful resource for the discovery of genetic variants affecting skeletal morphology. Domesticated and subsequently purebred dogs have undergone strong artificial selection for a broad range of skeletal variation, which include both the size and shapes of their bones. While the phenotypic variation between breeds is high, within-breed morphological variation is typically low. Approaches for defining genetic variants associated with canine morphology include quantitative within-breed analyses, as well as across-breed analyses, using breed standards as proxies for individual measurements. The ability to identify variants across the genomes of individual dogs can now be paired with precise measures of morphological variation to define the genetic interactions and the phenotypic effect of variants on skeletal morphology.

SOAT1 missense variant in two cats with sebaceous gland dysplasia.

Spontaneously arisen hereditary diseases in domestic animals provide an excellent opportunity to study the physiological functions of the altered genes. We investigated two 4-month-old sibling domestic short haired kittens with dry dark debris around the eyes, nose, and ears, dark crusting on the legs and a thin poor hair coat. Skin biopsies revealed abnormal sebaceous gland morphology with lack of normal sebocyte arrangement and differentiation. Hair follicles had a distorted silhouette, interpreted as a change secondary to the observed sebaceous gland dysplasia. Whole genome sequencing on both affected kittens and 65 genetically diverse feline genomes was performed. Filtering for variants that were present in both kittens but absent from the control genomes revealed a homozygous missense variant in SOAT1, encoding sterol O-acyltransferase 1. The protein is localized in the endoplasmic reticulum and catalyzes the formation of cholesteryl esters, an essential component of sebum and meibum. The identified SOAT1:c.1531G > A variant is predicted to change a highly conserved glycine residue within the last transmembrane domain of SOAT1, p.Gly511Arg. In mice, variants in Soat1 or complete knockout of the gene lead to the "hair interior defect" (hid) or abnormal Meibomian glands, respectively. SOAT1:c.1531G > A represents a plausible candidate variant for the observed sebaceous gland dysplasia in both kittens of this study. The variant was not present in 10 additional cats with a similar clinical and histopathological phenotype suggesting genetic heterogeneity. SOAT1 variants should be considered as potential cause in hereditary sebaceous gland dysplasias of humans and domestic animals.

A TNR Frameshift Variant in Weimaraner Dogs with an Exercise-Induced Paroxysmal Movement Disorder.

BACKGROUND: Some paroxysmal movement disorders remain without an identified genetic cause. OBJECTIVES: The aim was to identify the causal genetic variant for a paroxysmal dystonia-ataxia syndrome in Weimaraner dogs. METHODS: Clinical and diagnostic investigations were performed. Whole genome sequencing of one affected dog was used to identify private homozygous variants against 921 control genomes. RESULTS: Four Weimaraners were presented for episodes of abnormal gait. Results of examinations and diagnostic investigations were unremarkable. Whole genome sequencing revealed a private frameshift variant in the TNR (tenascin-R) gene in an affected dog, XM_038542431.1:c.831dupC, which is predicted to truncate more than 75% of the open read frame. Genotypes in a cohort of 4 affected and 70 unaffected Weimaraners showed perfect association with the disease phenotype. CONCLUSIONS: We report the association of a TNR variant with a paroxysmal dystonia-ataxia syndrome in Weimaraners. It might be relevant to include sequencing of this gene in diagnosing humans with unexplained paroxysmal movement disorders. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

STK36 splice site variant in an Australian Shepherd dog with primary ciliary dyskinesia.

Primary ciliary dyskinesia (PCD) represents a group of diseases characterized by impaired movement of cilia and subsequent health problems in diverse organ systems, notably the respiratory tract. Almost 50 candidate genes for PCD are known in humans. In this study, we investigated an Australian Shepherd dog with a history of recurrent respiratory infections and nasal discharge. A transmission electron microscopy investigation led to the diagnosis of PCD with central pair defect, in which the normal 9:2 arrangement of respiratory cilia was altered and reduced to a 9:0 arrangement. Whole genome sequencing data from the affected dog was obtained and searched for variants in PCD candidate genes that were not present in 918 control genomes from different breeds. This revealed a homozygous single base pair exchange at a splice site of STK36, XM_038585732.1:c.2868-1G>A. The mutant allele was absent from 281 additionally genotyped Australian Shepherd dogs. RT-PCR confirmed aberrant splicing in the affected dog with the skipping of exon 20 and the insertion of a cryptic exon, which is predicted to lead to a premature stop codon and truncation of 36% of the STK36 wild-type open reading frame, XP_038441660.1:(p.Met957Profs*11). STK36 variants were previously reported to cause PCD in humans and mice. The knowledge from other species together with the absence of the mutant allele in more than 1000 control dogs suggests STK36:c.2868-1G>A as the most likely candidate variant for PCD in the investigated case.

Heterozygous ATP2A2 missense variant identified in a Shih Tzu with Darier disease.

Darier disease is caused by heterozygous loss of function variants in the ATP2A2 gene encoding the endoplasmic/sarcoplasmic reticulum Ca2+ pump ATP2A2. Defective intracellular calcium signaling in the epidermis results in a loss of desmosomal adhesion and the development of characteristic skin lesions. In this study, we investigated a Shih Tzu that developed erythematous papules on the ventrum and, over time, the dorsal neck and a nodule in the right ear canal with secondary ear infection. Histopathologic examination demonstrated discrete foci of acantholysis affecting suprabasal layers of the epidermis. Whole genome sequencing of the affected dog identified a heterozygous missense variant, p.N809H, affecting an evolutionarily conserved amino acid residue of the ATP2A2 protein. The highly characteristic clinical and histopathologic findings together with a plausible variant in the only known functional candidate gene establish the diagnosis of canine Darier disease in the studied dog and highlight the potential of genetic analyses as complementary diagnostic approach in veterinary medicine.

SDR9C7 missense variant in a Chihuahua with non-epidermolytic ichthyosis.

Ichthyoses represent a heterogeneous group of cornification disorders that are associated with skin barrier defects. We investigated a 9-month-old Chihuahua showing excessive scale formation. Clinical and histopathological examinations revealed non-epidermolytic ichthyosis and a genetic defect was suspected. We therefore sequenced the genome of the affected dog and compared the data with 564 genetically diverse control genomes. Filtering for private variants identified a homozygous missense variant in SDR9C7, c.454C>T or p.(Arg152Trp). SDR9C7 is a known candidate gene for ichthyosis in humans and encodes the short-chain dehydrogenase/reductase family 9C member 7. The enzyme is involved in the production of a functional corneocyte lipid envelope (CLE), a crucial component of the epidermal barrier. Pathogenic variants in SDR9C7 have been described in human patients with autosomal recessive ichthyosis. We assume that the identified missense variant in the affected Chihuahua of this study impairs the normal enzymatic activity of SDR9C7 and thus prevents the formation of a functioning CLE, resulting in a defective skin barrier. To the best of our knowledge, this is the first report of a spontaneous SDR9C7 variant in domestic animals.

A CDH23 missense variant in Beauceron dogs with non-syndromic deafness.

Congenital coat-colour-related deafness is common among certain canine breeds especially those exhibiting extreme white spotting or merle patterning. We identified a non-syndromic deafness in Beauceron dogs characterised by a bilateral hearing loss in puppies that is not linked to coat colour. Pedigree analysis suggested an autosomal recessive transmission. By combining homozygosity mapping with whole genome sequencing and variant filtering in affected dogs we identified a CDH23:c.700C>T variant. The variant, located in the CHD23 (cadherin related 23) gene, was predicted to induce a CDH23:p.(Pro234Ser) change in the protein. Proline-234 of CDH23 protein is highly conserved across different vertebrate species. In silico tools predicted the CDH23:p.(Pro234Ser) change to be deleterious. CDH23 encodes a calcium-dependent transmembrane glycoprotein localised near the tips of hair-cell stereocilia in the mammalian inner ear. Intact function of these cilia is mandatory for the transformation of the acoustical wave into a neurological signal, leading to sensorineural deafness when impaired. By genotyping a cohort of 90 control Beauceron dogs sampled in France, we found a 3.3% carrier frequency. The CDH23:c.[700C>T] allele is easily detectable with a genetic test to avoid at-risk matings.

Dystrophin (DMD) Missense Variant in Cats with Becker-Type Muscular Dystrophy.

Muscular dystrophy due to dystrophin deficiency in humans is phenotypically divided into a severe Duchenne and milder Becker type. Dystrophin deficiency has also been described in a few animal species, and few DMD gene variants have been identified in animals. Here, we characterize the clinical, histopathological, and molecular genetic aspects of a family of Maine Coon crossbred cats with clinically mild and slowly progressive muscular dystrophy. Two young adult male littermate cats exhibited abnormal gait and muscular hypertrophy with macroglossia. Serum creatine kinase activities were highly increased. Histopathologically, dystrophic skeletal muscle exhibited marked structural changes including atrophic, hypertrophic, and necrotic muscle fibers. Immunohistochemistry showed irregularly reduced expression of dystrophin but the staining of other muscle proteins such as ß- and γ-sarcoglycans as well as desmin was also diminished. Whole genome sequencing of one affected cat and genotyping of the littermate found both to be hemizygous mutant at a single DMD missense variant (c.4186C>T). No other protein-changing variants in candidate genes for muscular dystrophy were detected. In addition, one clinically healthy male littermate was hemizygous wildtype, while the queen and one female littermate were clinically healthy, but heterozygous. The predicted amino acid exchange (p.His1396Tyr) resides in a conserved central rod spectrin domain of dystrophin. Various protein modeling programs did not predict major disruption of the dystrophin protein by this substitution, but the altered charge of the region may still affect protein function. This study represents the first genotype-to-phenotype correlation of Becker-type dystrophin deficiency in companion animals.

Independent DSG4 frameshift variants in cats with hair shaft dystrophy.

Investigations of hereditary phenotypes in spontaneous mutants may help to better understand the physiological functions of the altered genes. We investigated two unrelated domestic shorthair cats with bulbous swellings of the hair shafts. The clinical, histopathological, and ultrastructural features were similar to those in mice with lanceolate hair phenotype caused by loss-of-function variants in Dsg4 encoding desmoglein 4. We sequenced the genomes from both affected cats and compared the data of each affected cat to 61 control genomes. A search for private homozygous variants in the DSG4 candidate gene revealed independent frameshift variants in each case, c.76del or p.Ile26fsLeu*4 in case no. 1 and c.1777del or p.His593Thrfs*23 in case no. 2. DSG4 is a transmembrane glycoprotein located primarily in the extracellular part of desmosomes, a complex of adhesion molecules responsible for connecting the keratin intermediate filaments of neighbouring epithelial cells. Desmosomes are essential for normal hair shaft formation. Both identified DSG4 variants in the affected cats lead to premature stop codons and truncate major parts of the open-reading frame. We assume that this leads to a complete loss of DSG4 function, resulting in an incorrect formation of the desmosomes and causing the development of defective hair shafts. Together with the knowledge on the effects of DSG4 variants in other species, our data suggest that the identified DSG4 variants cause the hair shaft dystrophy. To the best of our knowledge, this study represents the first report of pathogenic DSG4 variants in domestic animals.