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Lavender foal syndrome (LFS) is a lethal neurological disease of the Arabian foal, caused by a mutation in the MYO5A gene. Affected foals are born with a characteristic coat dilution, lavender-grey or silver in tone, and with severe neurological signs: tetany, seizures and inability to stand and suckle. There is no treatment and most die or are euthanased in the first days. Carriers are healthy and of normal colour, so DNA testing is the only way to identify them.

LFS is concentrated in the Arabian horse, with a greater presence in lines of Egyptian ancestry. Gabreski et al. (2012) studied carrier allele frequencies and AbouEl Ela et al. (2023) documented its origin among Egyptian Arabians. There is no universal frequency: it depends on the population and the lines, so local data should be used before extrapolating figures.

- Coat dilution of lavender or greyish-silver tone at birth\n- Tetany and recurrent seizures from the first day\n- Opisthotonus and abnormal postures\n- Nystagmus or strabismus in some foals\n- Inability to stand and suckle\n- Paddling movements and rapid deterioration\n- Death or euthanasia in the first days of life

LFS was reported as a distinct condition in Arabian lines, with a particular presence in horses of Egyptian ancestry. In 2010, Brooks and colleagues combined genome-wide association with sequencing and identified a frameshift deletion in the MYO5A gene, which encodes myosin VA. This gene is the same one implicated in human Griscelli syndrome, which makes LFS a natural model of that disease. Since publication, carrier testing has been available and is recommended in breeding programmes for the breed.

- Test Arabian breeding animals, as a priority in lines with Egyptian ancestry\n- Never mate carrier with carrier: 25% risk of lavender foals\n- The birth of a lavender foal confirms that both parents are carriers: do not repeat the mating\n- A carrier may be mated to a clear animal, keeping only clear offspring for breeding\n- Lavender colour in an Arabian newborn is an immediate warning sign: confirm with DNA testing

The neonatal differential diagnosis includes neonatal maladjustment syndrome ('dummy foal'), hypoxic-ischaemic encephalopathy, sepsis and idiopathic seizures; the coat dilution is the guiding clue, although it may go unnoticed in low light. Confirmation is genetic. As it is a lethal disease with no treatment, the foal's welfare advises early euthanasia once the diagnosis is confirmed.

1. Brooks SA et al. 2010. Whole-genome SNP association in the horse: identification of a deletion in myosin Va responsible for Lavender Foal Syndrome. PLoS Genet. PMID: 20419149
2. Gabreski NA et al. 2012. Investigation of allele frequencies for Lavender foal syndrome in the horse. Anim Genet. PMID: 22497275
3. AbouEl Ela NH et al. 2023. Evidence for origin of lavender foal syndrome among Egyptian Arabian horses in Egypt. Equine Vet J. PMID: 35665534
4. Christen M et al. 2021. MYO5A Frameshift Variant in a Miniature Dachshund with Coat Color Dilution and Neurological Defects Resembling Human Griscelli Syndrome Type 1. Genes (Basel). PMID: 34680875
OMIA001501-9796.