Lavender Foal Syndrome (LFS), or coat colour dilution lethal (CCDL), is a rare and lethal disorder in Arabian horses and crossbreeds. Foals with LFS are born with neurological problems and a lightened coat colour. [1][2][3]

Lavender Foal Syndrome is a genetic condition that is caused by a mutation in the MYO5A gene, which affects nervous system function and skin pigmentation. Foals that inherit two copies of the gene from their parents develop LFS.

There is no cure or treatment available, and the condition is always fatal. Affected foals experience debilitating neurological symptoms, often resulting in euthanasia.

The only way to prevent Lavender Foal Syndrome is with responsible breeding practices and genetic testing in Arabian horse populations. By identifying carriers of the disorder and ensuring they do not mate with each other, the likelihood of producing foals with LFS is reduced.

Lavender Foal Syndrome in Horses

First described in 1996, Lavender Foal Syndrome (LFS) is caused by a fatal genetic mutation that affects the nervous system of Arabian foals.

Foals with LFS exhibit severe neurological signs, including incoordination and seizures. These foals cannot stand to nurse and die shortly after they are born.

Affected foals also display a unique coat colour, often described as a pale or silvery lavender, giving the condition its name.

The genetic mutation responsible for LFS is autosomal recessive, meaning that both parents must be carriers of the defective gene for their offspring to be affected. [3]

Awareness campaigns have been launched in various parts of the world to inform Arabian horse breeders about the importance of genetic testing. By testing potential breeding pairs, the prevalence of LFS can be reduced.

Prevalence

Most foals affected by LFS are Arabian horses from specific bloodlines, notably Egyptian Arabians. This breed sub-group originated in Egypt but is highly sought after in the United States. [1]

Approximately 10.3% of Egyptian Arabian horses and 1.6 – 1.8% of Arabians from other bloodlines are carriers of the gene responsible for Lavender Foal Syndrome.

Arabian Horse Genefits

The Arabian horse is an ancient breed known for its athletic endurance and spirited yet gentle nature. Arabians are distinguished by their dished face, high tail-carriage, arching neck and wide set eyes. [7]

The Arabian breed traces back to several founder horses, notably the “Godolphin Arabian,” the “Darley Arabian,” and the “Byerly Turk.” The extensive use of these founders in breeding led to a high prevalence of certain genetic alleles (mutations) among the Arabian population.

This limited genetic variation was further exacerbated by linebreeding, a selective breeding practice in which related animals are mated to preserve and emphasize desirable traits or phenotypes within a population. [8]

The combination of selective breeding and the Arabian’s limited initial gene pool led to the emergence of several recessive genetic conditions in the breed, including Lavender Foal Syndrome.

However, not all purebred Arabian populations carry the gene mutation responsible for LFS. [9] With genetic testing, responsible breeders can prevent LFS while maintaining the cherished traits of the Arabian breed.

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Clinical Signs

Foals with LFS are easiest to identify by the faded coat colour they display. Affected foals may appear silver, pewter, light chestnut, pale pink or lavender.

The following clinical signs are also reported in foals with LFS: [3][4][5][6]

  • Opisthotonos (backwards arching of the head, neck and spine)
  • Paddling movements with the limbs
  • Recumbency (laying down)
  • General weakness
  • Ataxia (lack of coordination)
  • Difficulty standing and nursing
  • Limb hyperextension
  • Nystagmus (Involuntary eye movements)

Affected foals may have exaggerated spinal reflexes and react strongly to touch. They may suffer from tetanic episodes that mimic seizures, in which the limbs, neck and back extend and contract. These episodes are not considered seizures as the foal’s mental state does not appear to be affected during this time. [6]

Foals with LFS often have difficulty adopting sternal recumbency, a position where the horse lies on its chest and abdomen. Most foals remain in a lateral recumbent position, lying on their side until they eventually pass away. [6]

In cases of Lavender Foal Syndrome, the dam typically has a normal pregnancy, but the delivery can be difficult. Signs of LFS may be mistaken for oxygen deprivation due to difficult birth or a spinal cord injury. [1]

Diagnosis

Diagnosing foals with LFS can be challenging since their initial clinical signs may mimic other neonatal conditions, such as encephalitis (inflammation of the brain). Moreover, LFS-affected foals might have normal clinical parameters, including consistent bloodwork results, further complicating the diagnosis. [1]

Before considering a diagnosis of LFS, your veterinarian will check the foal for signs of trauma, like a head injury, or any skull abnormalities that could be responsible for the neurological symptoms. [3]

The distinct pale coat colour, severe neurological deficits, and non-responsiveness to treatment are key features of LFS that differentiate it from other conditions.

Genetic testing is conducted to confirm a suspected diagnosis of Lavender Foal Syndrome. Your veterinarian will order a DNA test of the affected foal to confirm the presence of the MYO5A gene mutation responsible for LFS.

Differential Diagnosis

Differential diagnosis is the process of distinguishing a particular disease or condition from others that present with similar clinical features. When a foal presents with neurological symptoms, several conditions might be considered, including:

  • Neonatal septicaemia (NS): This life-threatening condition in newborn foals is characterized by a systemic bacterial infection that develops within the first few days of life. Affected foals exhibit a fever, lethargy, fast heart rate, weakness and may be unable to stand or nurse. [13]
  • Neonatal maladjustment syndrome: Also known as dummy foal syndrome this condition occurs when a foal experiences oxygen deprivation or other stressors during birth, resulting in a range of neurological abnormalities. Affected foals are born healthy but develop neurological symptoms shortly after birth, including unresponsiveness, confusion and difficult nursing. [12][14]
  • Occipitoatlantoaxial malformation (OAAM): This developmental defect occurs when the foal’s occipital, atlas and axis vertebrae are malformed or fused in the neck, compressing the spinal cord. This can cause incoordination, abnormal posture, inability to stand or nurse and paralysis of the legs. [12][15]
  • Neonatal Encephalopathy: This is another condition that can cause neurological signs in foals. It might be caused by a variety of factors, including perinatal asphyxia or a lack of oxygen during birth.

Other potential causes of neurological dysfunction in neonatal foals might include metabolic disturbances, toxic exposures, and congenital anomalies. Comprehensive veterinary evaluation and diagnostics are crucial to differentiate these causes.

MYO5A Gene Mutation

Lavender Foal Syndrome is caused by a mutation in the MYO5A gene, which not only affects neurological function but also influences coat colour. The MYO5A gene produces Myosin-Va, a protein essential during embryonic development.

Genes are segments of DNA that provide instructions for the cell to make specific proteins. Genetic mutations arise when alterations in the DNA sequence lead to the production of abnormal or non-functional proteins, potentially affecting the organism’s health and characteristics.

In the case of LFS, affected foals have a single base deletion in exon 30 of the MYO5A gene. This disrupts the synthesis of Myosin-Va, rendering it non-functional.

The MYO5A gene is particularly important during embryonic development, especially in the function of neural crest cells. These unique stem cell later differentiate into melanocytes that determine skin colour and neurons in the brain. [10]

Given the MYO5A gene’s involvement in the development of melanocytes and brain cells, it becomes clearer why foals with LF