Equine epitheliogenesis imperfecta in two american saddlebred foals is a lamina lucida defect.

This research investigates two foals of the American Saddlebred breed that manifested skin and dental abnormalities caused by a condition known as epitheliogenesis imperfecta (EI). The findings suggest that the observed defects may be due to a problem with laminin-5, a protein vital for skin’s structural integrity.

Necropsy Findings

• The researchers performed a necropsy on the two affected foals, revealing missing patches of epithelium, the outer layer of skin, as well as on the oral mucosa, lining of the mouth.
• On top of skin abnormalities, the foals also suffered from dental irregularities.
• No signs of ‘pyloric atresia’, a condition where the opening from the stomach into the small intestine is blocked, were discovered in either animal. This indicates that the defect was confined to the epithelial tissues.

Epidermis-Dermis Separation

• Upon histopathologic examination, a detachment of the epidermis, the outermost skin layer, from the dermis, the skin’s middle layer, was noted.
• The researchers concluded that this separation had occurred within the lamina lucida, a layer of the basal lamina (a layer separating the epidermis and the dermis), as witnessed under a transmission electron microscope.

Abnormal Hemidesmosomes

• The ultrastructure (detailed structure as viewed under an electron microscope) of the intact skin of the EI-affected foals showed irregular hemidesmosomes, connector proteins that play crucial roles in binding the outermost layer of the skin to its underlayer.
• Their abnormalities include a lack of a subbasal plate, an assembly of proteins required to maintain stability of the hemidesmosomes.

Similarity to Herlitz Junctional Epidermolysis Bullosa

• The morphological (structure and form of the organs) and ultrastructural defects seen in these foals were similar to defects witnessed in human newborns affected by Herlitz junctional epidermolysis bullosa (H-JEB), a severe, often fatal, skin disorder.
• H-JEB is caused by an aberration in one of the subunits of laminin-5, a protein that plays an integral role in securing the epidermis to the dermis of the skin.
• Due to the similarity between the two conditions, the study proposes the hypothesis that equine EI could be instigated by a defect within laminin-5.