Recent achievements in the genetic correction of keratinocytes isolated from patients with
junctional epidermolysis bullosa have paved the way to a gene
therapy approach for the disease. Because gene therapy protocols require preclinical validation in animals, we have characterized spontaneous animal models of
junctional epidermolysis bullosa. In this study we have elucidated the genetic basis of the hereditary junctional mechanobullous disease in the Belgian horse, a condition characterized by blistering of the skin and mouth epithelia, and exungulation (loss of the hoof). Immunofluorescence analysis associated the condition to the absent expression of the gamma2 chain of
laminin 5 and designated Lamc2 as the candidate gene. Comparative analysis of the nucleotide sequence of the full-length gamma2
cDNA isolated by reverse transcription polymerase chain reaction amplification of total
RNA purified from the epithelium of a
junctional epidermolysis bullosa foal and a healthy control disclosed a homozygous basepair insertion (1368insC) in the affected animal. Mutation 1368insC results in a downstream
premature termination codon and is predicted to cause absent expression of the
laminin gamma2
polypeptide. Our results also show that: (i) the horse
junctional epidermolysis bullosa genetically corresponds to the severe Herlitz form of
junctional epidermolysis bullosa in man; (ii) the amino acid sequence and structure of the horse
laminin gamma2 chain are virtually identical to the human counterpart; (iii) the moderate eruption of skin
blisters in the affected animals with respect to the human Herlitz
junctional epidermolysis bullosa patients correlates with the protection provided by hair. Our observations suggest that the affected foals are a convenient source of epithelial cells from tissues that cannot be obtained from human
junctional epidermolysis bullosa patients, and imply that hairless strains of animals with recessive skin disorders would be the best models for in vivo gene therapy approaches to skin blistering diseases.