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Gene or Region: LAMC2
Reference Variant: no change in LAMC2
Mutant Variant: insertion of C nucleotide
Affected Breeds: Belgian, Breton, Comtois
Research Confidence: High - Findings reproduced multiple studies
Explanation of Results: jeb1/jeb1 = homozygous for Junctional Epidermolysis Bullosa 1, trait expressed jeb1/n = heterozygous for Junctional Epidermolysis Bullosa 1, carrier n/n = no variant detected
Junctional Epidermolysis Bullosa 1 (JEB1), also known as red foot disease or hairless foal syndrome, results in the inability to produce the proteins needed to keep the skin on the body. Affected foals exhibit symptoms within days of birth, including blisters at the pressure points, detachment of the hooves, and oral ulcers. As there is no treatment, affected foals are humanely euthanized. JEB1 is an autosomal recessive condition, thus a horse must inherit two copies of the allele (jeb1/jeb1) to show any signs. Horses with only one copy of the variant (jeb1/n) are known as carriers due to their ability to produce affected foals.
LAMC2 is a subunit of a key component of basement membranes. Mutations in other subunits of this complex have been shown to result in JEB in many human populations. This particular mutation is a single base insertion that disrupts the normal amino acid sequence, resulting in an early stop codon and truncated protein.
Spirito F et al., “Animal models for skin blistering conditions: absence of laminin 5 causes hereditary junctional mechanobullous disease in the Belgian horse.” (2002) J Invest Dermatol. 119: 684-91. PMID: 12230513
Milenkovic D et al., “A mutation in the LAMC2 gene causes the Herlitz junctional epidermolysis bullosa (H-JEB) in two French draft horse breeds.” (2003) Genet Sel Evol. 35: 249-56. PMID: 12633536
Occipitoatlantoaxial Malformation 1 (OAAM1) is an inherited developmental condition predominantly found in Arabian horses, characterized by abnormal development of the cervical vertebrae leading to compression of the upper cervical cord and subsequent neurological damage.
Polysaccharide Storage Myopathy (PSSM) is a glycogen storage disorder in which affected horses have chronic episodes of exertional rhabdomyolysis (“tying-up”). Acute symptoms are an unwillingness to move and muscle damage following exercise. Moderate symptoms can usually be managed through a low-sugar/starch diet and exercise.
Recurrent Laryngeal Neuropathy (RLN) is a disease that results in loss of the neurons that open the larynx, significantly affecting performance in Thoroughbreds and other sport horses. It is an important issue for horses in competitive events because the resultant paralysis of the larynx leads to obstruction of air flow during intense exercise, creating the abnormal inspiratory noise that gives RLN its common name: “roaring”.
