A large deletion encompassing exon 2 of the ectodysplasin A (EDA) gene in a British blue crossbred calf with hypohidrotic ectodermal dysplasia.

BACKGROUND: Hypohidrotic ectodermal dysplasia (HED) is a congenital syndrome of mammals affecting organs and tissues of ectodermal origin characterized by absence or hypoplasia of hair, teeth, and eccrine glands. The disorder has been reported in several species, including humans, mice, dogs and cattle, associated with variants in genes affecting the ectodysplasin pathway, including the X-linked ectodysplasin A (EDA) gene. Until now, nine pathogenic variants have been found in the bovine EDA gene. Here we report a novel variant in EDA in a crossbreed male Belgian Blue calf with HED, and provide an overview of the phenotypic and allelic heterogeneity of EDA-related forms of HED in cattle. CASE PRESENTATION: A 45-day-old male crossbreed British Blue calf was referred with congenital hypotrichosis, oligodontia and omphalitis. On histopathological examination of the nasal planum, nasolabial glands and ducts were not observed. The density of hair follicles was low, and they were small, with a predominance of telogen-phase hairs, and some serocellular crusts. The phenotype of the calf resembled that of HED. Whole-genome sequencing (WGS) was performed and revealed a 21,899 base-pair deletion encompassing the coding exon 2 of EDA, predicted to result in an altered transcript and aberrant protein. CONCLUSIONS: The clinicopathological and genetic findings were consistent with a case of X-linked HED. A very similar EDA deletion has been previously reported in a family of Holstein cattle with HED. The newly identified hemizygous EDA loss-of-function variant is certainly pathogenic and therefore is the genetic cause for the observed phenotype. This case report provides an additional example of the potential of WGS-based precise diagnostics in livestock species such as cattle to increase the diagnostic yield in rare diseases.

A large deletion in the COL2A1 gene expands the spectrum of pathogenic variants causing bulldog calf syndrome in cattle.

BACKGROUND: Congenital bovine chondrodysplasia, also known as bulldog calf syndrome, is characterized by disproportionate growth of bones resulting in a shortened and compressed body, mainly due to reduced length of the spine and the long bones of the limbs. In addition, severe facial dysmorphisms including palatoschisis and shortening of the viscerocranium are present. Abnormalities in the gene collagen type II alpha 1 chain (COL2A1) have been associated with some cases of the bulldog calf syndrome. Until now, six pathogenic single-nucleotide variants have been found in COL2A1. Here we present a novel variant in COL2A1 of a Holstein calf and provide an overview of the phenotypic and allelic heterogeneity of the COL2A1-related bulldog calf syndrome in cattle. CASE PRESENTATION: The calf was aborted at gestation day 264 and showed generalized disproportionate dwarfism, with a shortened compressed body and limbs, and dysplasia of the viscerocranium; a phenotype resembling bulldog calf syndrome due to an abnormality in COL2A1. Whole-genome sequence (WGS) data was obtained and revealed a heterozygous 3513 base pair deletion encompassing 10 of the 54 coding exons of COL2A1. Polymerase chain reaction analysis and Sanger sequencing confirmed the breakpoints of the deletion and its absence in the genomes of both parents. CONCLUSIONS: The pathological and genetic findings were consistent with a case of "bulldog calf syndrome". The identified variant causing the syndrome was the result of a de novo mutation event that either occurred post-zygotically in the developing embryo or was inherited because of low-level mosaicism in one of the parents. The identified loss-of-function variant is pathogenic due to COL2A1 haploinsufficiency and represents the first structural variant causing bulldog calf syndrome in cattle. Furthermore, this case report highlights the utility of WGS-based precise diagnostics for understanding congenital disorders in cattle and the need for continued surveillance for genetic disorders in cattle.

A de novo variant in OTX2 in a lamb with otocephaly.

BACKGROUND: Otocephaly is a rare lethal malformation of the first branchial arch. While the knowledge on the causes of otocephaly in animals is limited, different syndromic forms in man are associated with variants of the PRRX1 and OTX2 genes. CASE PRESENTATION: A stillborn male lamb of the Istrian Pramenka sheep breed showed several congenital craniofacial anomalies including microstomia, agnathia, aglossia, and synotia. In addition, the lamb had a cleft palate, a small opening in the ventral neck region, a cystic oesophagus and two hepatic cysts. The brain was normally developed despite the deformed shape of the head. Taken together the findings led to a diagnosis of otocephaly. Whole-genome sequencing was performed from DNA of the affected lamb and both parents revealing a heterozygous single nucleotide variant in the OTX2 gene (Chr7: 71478714G > A). The variant was absent in both parents and therefore due to a de novo mutation event. It was a nonsense variant, XM_015097088.2:c.265C > T; which leads to an early premature stop codon and is predicted to truncate more than 70% of the OTX2 open reading frame (p.Arg89*). CONCLUSIONS: The genetic findings were consistent with the diagnosis of the otocephaly and provide strong evidence that the identified loss-of-function variant is pathogenic due to OTX2 haploinsufficiency. The benefits of trio-based whole-genome sequencing as an emerging tool in veterinary pathology to confirm diagnosis are highlighted.

APOB-associated cholesterol deficiency in Holstein cattle is not a simple recessive disease.

In 2015, cholesterol deficiency (CD) was reported for the first time as a new recessive defect in Holstein cattle. After GWAS mapping and identification of a disease-associated haplotype, a causative loss-of-function variant in APOB was identified. CD-clinically affected APOB homozygotes showed poor development, intermittent diarrhea and hypocholesterolemia and, consequently, a limited life expectation. Herein, we present a collection of 18 cases clinically diagnosed as CD-affected APOB heterozygotes. CD-clinically affected heterozygotes show reduced cholesterol and triglyceride blood concentrations. The differences in total blood cholesterol and triglycerides between nine CD-clinically affected and 36 non-affected heterozygotes were significant. As only some APOB heterozygotes show the clinical CD phenotype, we assume that the penetrance is reduced in heterozygotes compared to the fully penetrant effect observed in homozygotes. We conclude that APOB-associated CD represents most likely an incomplete dominant inherited metabolic disease with incomplete penetrance in heterozygotes.

Chromosomal imbalance in pigs showing a syndromic form of cleft palate.

BACKGROUND: Palatoschisis or cleft palate is a known anomaly in pigs resulting in their death. However, little is known about its aetiology. A detailed description of the phenotype was derived from necropsy and by computed tomography revealing that all 20 cases also exhibited hypodontia and renal cysts. Furthermore, a genetic origin was assumed due to dominant inheritance as all 20 recorded cases were confirmed offspring of a single boar. RESULTS: Single nucleotide variant (SNV) genotyping data were used to map the defect in the porcine genome and led to the detection of a chromosomal imbalance in the affected offspring. Whole genome sequencing of an affected piglet and a normal full sib was used to identify a chromosomal translocation and to fine map the breakpoints in the genome. Finally, we proved that the boar, which sired the malformed piglets, carried a balanced translocation. The detected translocation of Mb-sized segments of chromosome 8 and 14 had not been previously observed during karyotyping. All affected offspring were shown to be carriers of a partial trisomy of chromosome 14 including the FGFR2 gene, which is associated with various dominant inherited craniofacial dysostosis syndromes in man, and partial monosomy of chromosome 8 containing MSX1 known to be associated with tooth agenesis and orofacial clefts in other species. CONCLUSIONS: This study illustrates the usefulness of recently established genomic resources in pigs. In this study, the application of genome-wide genotyping and sequencing methods allowed the identification of the responsible boar and the genetic cause of the observed defect. By implementing systematic surveillance, it is possible to identify genetic defects at an early stage and avoid further distribution of congenital disorders.