Lavender Foal Syndrome (LFS)

Lavender Foal Syndrome is an inherited neurological disorder affecting primarily Arabian horses. It is characterized by a combination of unusual coat dilution and severe neurological abnormalities. The disease is incurable and invariably results in the death of the foal or euthanasia.

Affected foals are born with unusually light-colored coats, described as lavender, light gray, pewter, or light chestnut. At the same time, they exhibit severe neurological signs, including an inability to stand and suckle, seizures resembling tetanus, marked backward arching of the head and neck (opisthotonus), stiffness or paddling movements of the limbs, and involuntary eye movements (nystagmus). These signs may resemble other diseases affecting newborn foals, such as sepsis or neonatal encephalopathy; however, the characteristic coat color is highly suggestive of LFS.

The syndrome is caused by the c.4249del mutation in the MYO5A gene, which encodes the motor protein myosin Va. This protein is involved in the transport of pigment-containing melanosomes as well as the transport of substances within nerve cells. Therefore, the mutation causes both abnormal pigment distribution in the coat and severe impairment of the nervous system.

The mutation is inherited in an autosomal recessive manner. This means that the disease develops only in individuals that inherit the mutated allele from both parents. Carriers of the mutated allele are clinically healthy but can pass the mutation on to their offspring. When two heterozygous carriers are mated, theoretically 25% of the offspring will be genetically clear, 50% will be carriers, and 25% will inherit the mutated allele from both parents and therefore be affected by the disease.

Genetic testing makes it possible to reliably identify carriers of the mutation and prevent the birth of affected foals through appropriate breeding planning.

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References:

Brooks, SA., Gabreski, N., Miller, D., Brisbin, A., Brown, HE., Streeter, C., Mezey, J., Cook, D., Antczak, DF. : Whole-genome SNP association in the horse: identification of a deletion in myosin Va responsible for Lavender Foal Syndrome. PLoS Genet 6:e1000909, 2010. Pubmed reference: 20419149