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Gene or Region: MYO5A
Reference Variant: C
Mutant Variant: -
Affected Breeds: Arabian
Research Confidence: High confidence - Findings reproduced multiple studies
Explanation of Results: lfs/lfs = homozygous for Lavender Foal Syndrome, lethal lfs/n = heterozygous for Lavender Foal Syndrome, carrier n/n = no variant detected
Lavender Foal Syndrome (LFS), also known as coat color dilution lethal, is a neurological dysfunction in newborn foals. Symptoms are apparent at birth and include seizures, severe hyper-extension of limbs, neck and back, stiff paddling leg movements, involuntary eye movement and inability to stand or sit upright. The coat usually has a dilute color that ranges in shade from silver to a pale lavender/pink. As there is no treatment, affected foals are humanely euthanized. LFS is an autosomal recessive condition, thus a horse must inherit two copies of the allele (LFS/LFS) to show any signs. Horses with only one copy of the allele (LFS/n) are known as carriers due to their ability to produce affected foals.
MYO5A functions as part of a trafficking complex that serves to move important molecules in pigment cells and neurons. Mutations in humans result in Griscelli syndrome, which is characterized by dilute hair and neurological dysfunction. The LFS mutation is a single base deletion that results in a premature stop codon, and thus a truncated protein.
Brooks SA et al., “Whole-genome SNP association in the horse: identification of a deletion in myosin Va responsible for Lavender Foal Syndrome.” (2010) PLoS Genet. 6: e1000909. PMID: 20419149
Gabreski NA et al., “Investigation of allele frequencies for Lavender foal syndrome in the horse.” (2012) Anim Genet. 43: 650. PMID: 22497275
Tarr CJ et al., “The carrier prevalence of severe combined immunodeficiency, lavender foal syndrome and cerebellar abiotrophy in Arabian horses in South Africa.” (2014) Equine Vet J. 46: 512-4. PMID: 24033554
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”.
