WGS of Mouton Vendéen sheep with Epidermolysis Bullosa

Junctional Epidermolysis Bullosa (EB) is a severe congenital disease affecting the skin at the extremities of the limbs and the mucous membranes. In sheep, this recessive disease causes perinatal death of affected lambs. Multiple observations of EB cases were recently reported in the French Mouton Vendéen meat sheep breed. Skin biopsies of 6 affected lambs and when available, blood samples from the parents (n = 7) and unaffected full-sib lambs (n = 4) were collected for genomic DNA extraction. Based on the hypothesis of a recessive transmission of a deleterious variant, we have performed whole-genome sequencing of 2 unrelated EB-affected lambs (supposed homozygous carriers) and 1 unaffected full-sib (supposed heterozygous or non-carrier). The strategy focused on 13 candidate genes already associated with EB or skin fragility syndrome in several species, and mainly belonging to the collagen, laminin, integrin and keratin families. After variant analysis of these 13 genes, we have identified a novel SNP in the exon 23 of the ITGB4 gene of the integrin family (OAR11_v4.0, g.54799925G>A) whose variant allele causes a premature stop codon (p.Arg885*). By a specific RFLP assay, we have determined that all EB-affected lambs were homozygous for this variant allele, their parents were heterozygous and the full-sibs were either heterozygous or non-carrier, fitting well with a recessive mutation segregation. Through a large set of genotyping of renewal ewe lambs from the same annual cohort (n = 1227), the population allele frequency was estimated to be 6.8%. The discovery of a new mutation in ovine ITGB4 enhances the role of this gene in EB etiology and is an important molecular tool to improve the selection scheme management of the Mouton Vendéen breed to limit the dissemination of this disease.