APPLIED MEDICINE: CLINICAL PATHOLOGY AND DERMATOLOGY


areas of ulcers are along the coronary bands, which may progress to sloughing of the hoof.6–9 The clinical, histopathological, ultrastructural,


Fig. 1. Newborn Belgian foal shows characteristic skin lesions of junctional epidermolysis bullosa-Herlitz form.


tering occurs in the dermis (or sublamina densa). The fourth type of EB is the Kindler syndrome, which is a mixed type of EB that exhibits multiple cleavage planes within the affected skin.1,3 JEB-Herlitz (JEB-H) represents the most severe


form of EB, which is characterized by generalized, extensive mucocutaneous blistering at birth with erosions of the skin and mucous membranes, and dental enamel hypoplasia.3,4 In humans, the dis- ease is lethal in early childhood.1 JEB-H is most often caused by homozygous null mutations in the genes LAMA3, LAMB3,or LAMC2, each gene encod- ing for one of the three chains of the heterotrimer laminin-332 (previously laminin-5).3 The Herlitz form of JEB is the result of complete absence of laminin-332.4,5 Laminin-332 is a major adhesion protein within


the basement membrane zone of the skin and mu- cous epithelia that provides stable anchorage of basal epithelial cells (keratinocytes) to the under- lying dermis by connecting the hemidesmosomal component64 integrin to collagen VII–containing anchoring fibrils.4 Laminin-332 is an essential component of the dermal-epidermal basement mem- brane.5 The usual mode of transmission is auto- somal recessive.3,4 In North America, reports of a junctional mecha- nobullous disease in Belgian foals were first pub- lished in the late 1980s.6–8 The most consistent skin changes are irregular, round, red, and ulcer- ated areas over the bony prominences of the hocks, stifles, hips, carpi, elbows, and fetlocks (Fig. 1). The severity and extent of the skin lesions progress with age. Affected foals usually have very exten- sive oral erosions and ulcers, especially around the base of the incisor teeth. One of the most charac- teristic findings is that the temporary incisor teeth, which are not usually noticed until 8 to 14 days of age, are visible at birth. The teeth are very white and have irregular serrated edges, with pitted enamel. Excessive amounts of blood-tinged saliva may occur as a result of oral ulceration. Irregular


and immunohistochemical findings have shown that the disease in North American Belgian draft foals fits all the criteria of the JEB-H form of EB.10 The mutation responsible for this particular form in Belgian draft horses was first identified on Janu- ary 24, 2001, by researchers at the INSERM 634 Laboratory, University of Nice, France.10 The mu- tation is a cytosine insertion in the genomic nucleic acid sequence of affected horses at position 1368 of the laminin2-encoding polynucleotide, resulting in a frame shift that leads to a premature termination codon and absent expression of the LAMC2 gene.10 An autosomal recessive mode of inheritance of this mutation was verified.10 After the identification of the LAMC2 mutation, a commercial polymerase chain reaction (PCR) test was developed at the Veterinary Genetics Labora- tory (VGL), School of Veterinary Medicine, Univer- sity of California-Davis. This test was performed on DNA samples with fluorescence-labeled primers designed to amplify the region containing the mu- tation. The mutation is a single base insertion, and thus carriers have a PCR product that is one base longer than the normal allele. The single base difference is detected by analysis of the PCR prod- ucts by capillary electrophoresis on ABI 3730 DNA sequencer.9 The availability of a commercial PCR test and appropriate genetic counseling made it possible for Belgian draft horse breeders to avoid the financial and genetic losses associated with the birth of JEB-H foals. Commencing on November 1, 2002, the Belgian Draft Horse Corporation of America (BDHCA) instituted rules that require the sire of a foal being registered to have been DNA-profiled and JEB-tested. This testing program is organized by the corporation office. The breed association pro- vides hair sample collection information and forms to the owners of horses to be tested. Samples are submitted to the VGL for testing, and results are reported directly to the breed association office. The JEB results are printed on the Certificate of Registry. The Canadian Belgian Horse Association (CBHA) instituted the same requirements that com- menced on January 1, 2003. The testing of mares for the LAMC2 mutation has been on a voluntary basis; however, when mares are bred by artificial insemi- nation with frozen semen they are required to be DNA- and JEB-tested. Foals resulting from frozen semen insemination are also required to be DNA- and JEB-tested. The aim of the genetic testing pro- gram is (1) to prevent the birth of JEB-H Belgian foals and (2) to reduce the number of carrier animals in the population.


2. Materials and Methods


Until December 31, 2012, mane hair root samples from 1785 stallions, 301 mares, and nine geldings


AAEP PROCEEDINGS  Vol. 59  2013 511


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