A frameshift insertion in FA2H causes a recessively inherited form of ichthyosis congenita in Chianina cattle.

The aim of this study was to characterize the phenotype and to identify the genetic etiology of a syndromic form of ichthyosis congenita (IC) observed in Italian Chianina cattle and to estimate the prevalence of the deleterious allele in the population. Sporadic occurrence of different forms of ichthyosis including IC have been previously reported in cattle. However, so far, no causative genetic variant has been found for bovine IC. Nine affected cattle presenting congenital xerosis, hyperkeratosis and scaling of the skin as well as urolithiasis and cystitis associated with retarded growth were examined. Skin histopathology revealed a severe, diffuse orthokeratotic hyperkeratosis with mild to moderate epidermal hyperplasia. The pedigree records indicated a monogenic recessive trait. Homozygosity mapping and whole-genome sequencing allowed the identification of a homozygous frameshift 1 bp insertion in the FA2H gene (c.9dupC; p.Ala4ArgfsTer142) located in a 1.92 Mb shared identical-by-descent region on chromosome 18 present in all cases, while the parents were heterozygous as expected for obligate carriers. These findings enable the selection against this sub-lethal allele showing an estimated frequency of ~ 7.5% in Chianina top sires. A sporadic incidence of mild clinical signs in the skin of heterozygous carriers was observed. So far, pathogenic variants affecting the encoded fatty acid 2-hydroxylase catalyzing the synthesis of 2-hydroxysphingolipids have been associated with myelin disorders. In conclusion, this study represents the first report of an FA2H-related autosomal recessive inherited skin disorder in a mammalian species and adds FA2H to the list of candidate genes for ichthyosis in humans and animals. Furthermore, this study provides a DNA-based diagnostic test that enables selection against the identified pathogenic variant in the Chianina cattle population. However, functional studies are needed to better understand the expression of FA2H in IC-affected Chianina cattle.

A KRT71 Loss-of-Function Variant Results in Inner Root Sheath Dysplasia and Recessive Congenital Hypotrichosis of Hereford Cattle.

Genodermatoses, such as heritable skin disorders, mostly represent Mendelian conditions. Congenital hypotrichosis (HY) characterize a condition of being born with less hair than normal. The purpose of this study was to characterize the clinicopathological phenotype of a breed-specific non-syndromic form of HY in Hereford cattle and to identify the causative genetic variant for this recessive disorder. Affected calves showed a very short, fine, wooly, kinky and curly coat over all parts of the body, with a major expression in the ears, the inner part of the limbs, and in the thoracic-abdominal region. Histopathology showed a severely altered morphology of the inner root sheath (IRS) of the hair follicle with abnormal Huxley and Henle's layers and severely dysplastic hair shafts. A genome-wide association study revealed an association signal on chromosome 5. Homozygosity mapping in a subset of cases refined the HY locus to a 690 kb critical interval encompassing a cluster of type II keratin encoding genes. Protein-coding exons of six positional candidate genes with known hair or hair follicle function were re-sequenced. This revealed a protein-changing variant in the KRT71 gene that encodes a type II keratin specifically expressed in the IRS of the hair follicle (c.281delTGTGCCCA; p.Met94AsnfsX14). Besides obvious phenocopies, a perfect concordance between the presence of this most likely pathogenic loss-of-function variant located in the head domain of KRT71 and the HY phenotype was found. This recessive KRT71-related form of hypotrichosis provides a novel large animal model for similar human conditions. The results have been incorporated in the Online Mendelian Inheritance in Animals (OMIA) database (OMIA 002114-9913).

Clinicopathological and Genomic Characterization of a Simmental Calf with Generalized Bovine Juvenile Angiomatosis.

Bovine juvenile angiomatosis (BJA) comprises a group of single or multiple proliferative vascular anomalies in the skin and viscera of affected calves. The purpose of this study was to characterize the clinicopathological phenotype of a 1.5-month-old Simmental calf with multiple cutaneous, subcutaneous, and visceral vascular hamartomas, which were compatible with a generalized form of BJA, and to identify genetic cause for this phenotype by whole-genome sequencing (WGS). The calf was referred to the clinics as a result of its failure to thrive and the presence of multiple cutaneous and subcutaneous nodules, some of which bled abundantly following spontaneous rupture. Gross pathology revealed similar lesions at the inner thoracic wall, diaphragm, mediastinum, pericardium, inner abdominal wall, and mesentery. Histologically, variably sized cavities lined by a single layer of plump cells and supported by a loose stroma with occasional acute hemorrhage were observed. Determined by immunochemistry, the plump cells lining the cavities displayed a strong cytoplasmic signal for PECAM-1, von Willebrand factor, and vimentin. WGS revealed six private protein-changing variants affecting different genes present in the calf and absent in more than 4500 control genomes. Assuming a spontaneous de novo mutation event, one of the identified variants found in the PREX1, UBE3B, PCDHGA2, and ZSWIM6 genes may represent a possible candidate pathogenic variant for this rare form of vascular malformation.

A de novo mutation in KRT5 in a crossbred calf with epidermolysis bullosa simplex.

A 6-day-old Belgian Blue-Holstein calf was referred because of a syndrome resembling epidermolysis bullosa simplex (EBS). The clinical phenotype included irregular and differently sized erosions and ulcerations spread over the body, in particular on the limbs and over bone prominences, as well as in the nasal planum and oral mucosa. Blisters were easily induced by rubbing the skin. The skin lesions displayed a clear dermal-epidermal separation at the level of the basal cell layer. Post mortem examination revealed erosions in the pharynx, proximal esophagus, and rumen. Whole-genome sequencing revealed a heterozygous disruptive in-frame deletion variant in KRT5 (c.534_536delCAA). Genotyping of both parents confirmed the variant as de novo mutation. Clinicopathological and genetic findings were consistent with the diagnosis of KRT5-related EBS providing the second example of a spontaneous mutation causing epidermolysis bullosa in cattle.

A Heterozygous Missense Variant in the COL5A2 in Holstein Cattle Resembling the Classical Ehlers-Danlos Syndrome.

Classical Ehlers-Danlos syndrome (cEDS) is a heritable connective tissue disorder characterized by variable degrees of skin hyperextensibility and fragility, atrophic scarring, and generalized joint hypermobility. The purpose of this study was to characterize the clinicopathological phenotype of a cEDS-affected Holstein calf and to identify the causative genetic variant associated with the disorder by whole-genome sequencing (WGS). A 3-day-old female Holstein calf was referred because of easily induced skin detachment and hyperextensibility in the neck. A complete clinical investigation was performed in the calf, dam, and maternal-grandmother. The calf and dam showed hyperextensibility of the neck skin and atrophic scarring; additionally, the calf presented skin fragility. Moreover, the histopathology of biopsies from the calf and its dam showed that the collagen bundles in affected skin areas were wavy, short, thin, and surrounded by edema and moderate to severe acute hemorrhages. Genetic analysis revealed a private heterozygous missense variant in COL5A2 (c.2366G>T; p.Gly789Val) that was present only in the calf and dam. This confirmed the diagnosis of cEDS and represents the first report of a causal variant for cEDS in cattle and the first COL5A2-related large animal model.

Is a de novo nonsense variant in the ASPDH gene the cause of ulcerative skin lesions in a Holstein calf?

BACKGROUND: Genetic skin diseases in cattle are rare. CLINICAL SUMMARY: A 7-week-old female Holstein calf was presented with epidermal lesions and alopecia in the caudal region of the ears and on the neck, as well as deep bilateral ulcerative lesions on the palmar aspect of the metacarpi and dorsal aspect of the right metacarpus. Clinical, pathological and histopathological examination of the calf was suggestive of a subepidermal vesicular dermatosis. Genetic analysis identified a de novo non-sense variant affecting the aspartate dehydrogenase domain containing (ASPDH) gene, which might be associated with the formation of subepidermal vesicles in this case. CONCLUSION AND CLINICAL IMPORTANCE: The observed phenotype in the calf may represent a novel form of a vesicular skin disorder. Haploinsufficiency of the ASPDH gene might be considered as a possible cause.

Phylogenetic relationship of Ornithobacterium rhinotracheale isolated from poultry and diverse avian hosts based on 16S rRNA and rpoB gene analyses.

BACKGROUND: Ornithobacterium (O.) rhinotracheale is an emerging bacterial pathogen in poultry and not fully understood to date. Because of its importance particularly for the global turkey meat industry, reliable diagnostic and characterization methods are needed for early treatment and in future for better vaccine production. The host range of birds infected by O. rhinotracheale or carrying the bacterium in their respiratory tract has constantly increased raising important epidemiological and taxonomic questions for a better understanding of its diversity, ecology and transmission cycles. The purpose of this study was to introduce partial rpoB gene sequencing for O. rhinotracheale into routine diagnostics to differentiate strains isolated from poultry and more diverse avian hosts (i.e., birds of prey, corvids and pigeons) and to compare phylogenetic relationships with results from 16S rRNA gene analysis and multilocus sequence typing (MLST). RESULTS: Partial 16S rRNA gene analysis revealed a high level of homogeneity among the 65 investigated O. rhinotracheale sequences with similarity values ranging from 98.6 to 100% between sequences from non-galliform and poultry species. The corresponding rpoB gene sequences were heterogeneous and ranged in their similarity values from 85.1 to 100%. The structure of the rpoB tree was in strong correlation with previous MLST results revealing three main clusters A (poultry and birds of prey), B (poultry, birds of prey and corvids) and C (pigeons), which were clearly separated from each other. CONCLUSIONS: By using partial sequences from a single gene, the rpoB gene analysis is in good agreement with MLST results with a slight decrease in resolution to distinguish more similar strains. The present results provide strong evidence that traditional phenotypic and genetic methods may not properly represent the heterogeneous group of bacteria classified as O. rhinotracheale. From housekeeping gene analyses, it is very likely that the genus Ornithobacterium includes additional species and partial rpoB gene sequencing can be recommended as fast, cost-effective and readily available method to identify strains and differentiate between O. rhinotracheale and Ornithobacterium-like bacteria.