Each February, I enjoy volunteering on the Horse Show Committee of our local Livestock Exposition. In addition to checking health papers at the arrivals station, I work at the education center for schoolchildren, where one of our star attractions is a huge (20 hands high) Flemish war horse. Unfortunately, extraordinary size, in both humans and horses, is often associated with devastating health problems, especially when combined with inbreeding. This paper by Milenkovic and colleagues (2003) describes a mutation in a laminin gene that causes a lethal skin disorder, Herlitz junctional epidermolysis bullosa (H-JEB), in French draft horses.
Flemish Draft Horse, ancestral breed for many European draft horses. This horse is chestnut in coloration, and has an extremely gentle and calm disposition.
Epidermolysis bullosa refers to a group of skin blistering and fragility disorders; the H-JEB variety is characterized by an autosomal recessive pattern of inheritance, separation of the epidermal and dermal skin layers, and mutations in the gene encoding the laminin 5 adhesion protein component of hemidesmosome anchors. Junctional epidermolysis bullosa, caused by a mutation in the LAMC2 gene, has been reported in Belgian draft horses (Spirito et al., 2002), and Milenkovic et al. (2003) examined this same gene in affected Trait Breton and Trait Comtois draft horses.
Pedigrees, skin samples from affected foals, and genomic DNA from blood samples were collected for 19 Trait Comtois and 47 Trait Breton horses. The PCR (polymerase chain reaction) technique and DNA sequencing were used to look for presence of the exon 10 mutation in the LAMC2 gene, and linkage disequilibrium analysis between the JEB phenotype and this mutation was performed. The phenotype, which includes skin blistering, skin and mucosal ulceration, and loss of hooves, has a lethal prognosis, such that affected foals required euthanasia soon after birth. Histological analysis of the skin samples revealed absence of the epidermis, particularly on the lower legs, as well as severe ulcers on the mucosa of the mouth. One or two founder stallions, probably heterozygous for the LAMC2 mutation, were identified in the pedigrees for these two French draft horse breeds. Apart from the scientific importance of a mutation that affects a structural protein essential for skin development in both humans and horses, this study is extremely useful for breeders of the Breton and Comtois draft horses.
* Milenkovic, D., Chaffaux, S., Taourit, S., Guérin, G. (2003). a mutation in the LAMC2 gene causes the Herlitz junctional epidermolysis bullosa (H-JEB) in two French draft horse breeds. Genet. Sel. Evol. 35, 249-256.
Spirito F., Charlesworth A., Linder, K., Ortonne J.P., Baird J., Meneguzzi, G. (2002). Animal models for skin blistering conditions: absence of laminin 5 causes hereditary junctional mechanobullous disease in the Belgian horse. J. Invest. Dermatol. 3, 684-691.
* primary paper discussed in this post, a “Special Horse Show Edition” of Weekend Disease Models
Milenkovic, D., Chaffaux, S., Taourit, S., Guï¿½rin, G. (2003). . Genetics Selection Evolution, 35(2), 249-256. DOI: 10.1051/gse:2003007