section name header

Basics ⬇

Outline

BASICS

Overview!!navigator!!

LFS, or coat color dilution lethal, is a tetanic neurologic syndrome of neonatal foals of Egyptian Arabian breeding. The disease is rare and the outcome is uniformly fatal in affected individuals. The disease is genetic and appears to have an autosomal recessive mode of inheritance.

Signalment!!navigator!!

  • LFS affects neonatal Arabian foals of pure Egyptian lineage, with clinical signs of disease noted immediately after birth
  • Cases involving other breeds have not been reported, and there is no apparent sex predilection

Signs!!navigator!!

  • Persistent seizure-like activity with pronounced extensor rigidity, opisthotonos, and frequent paddling
  • Apparent blindness
  • Failure to stand
  • Preserved, often strong, suckle reflex
  • Dilute coat color, classically silver-gray “lavender,” but may also be dilute chestnut or pale slate gray
  • Affected foals are not always of “lavender” coloration

Causes and Risk Factors!!navigator!!

A genetic basis has been documented with an autosomal recessive mode of inheritance. A single point mutation in the myosin Va gene has been associated with the condition.

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Neonatal maladjustment syndrome
  • Neonatal septicemia
  • Idiopathic epilepsy of Arabian foals—also noted in Arabian foals of Egyptian breeding, but affected foals are normal at birth and between episodes, and may “outgrow” the seizure disorder by 12–18 months of age
  • Occipitoatlantoaxial malformation—also noted more commonly in Arabian foals. Palpation and diagnostic imaging (radiography) confirm this diagnosis
  • Hydrocephalus—seizures are characteristic, and affected foals often display visible doming of the skull

CBC/Biochemistry/Urinalysis!!navigator!!

The CBC is typically unremarkable, unless septicemia develops. Serum biochemistry analysis is usually normal, but it may display evidence that the foal has not nursed its dam or received colostrum (hypoproteinemia, hypoglobulinemia, hypogammaglobulinemia, and hypoglycemia).

Other Laboratory Tests!!navigator!!

  • Definitive diagnosis can be achieved through genetic testing of affected foals
  • Serum/plasma immunoglobulin G will be low if there has been inadequate ingestion of colostrum

Imaging!!navigator!!

Skull and cervical spinal radiography may be performed to rule out congenital bony malformations in these regions, but imaging is not useful for supporting a diagnosis of LFS.

Other Diagnostic Procedures!!navigator!!

Histopathologic analysis of skin biopsy specimens may reveal melanin clumping and follicular dysplasia in affected individuals.

Pathologic Findings!!navigator!!

No gross or histologic lesions of the central nervous system have been noted during postmortem examination of affected foals. Evidence of self-trauma inflicted during paddling and changes associated with recumbency (dependent pulmonary atelectasis, decubital ulceration) are often the only gross postmortem findings. Melanin clumping in the dermal follicular bulbs and hair shafts may be noted histologically.

Treatment ⬆ ⬇

TREATMENT

Affected foals may be referred to a tertiary care facility for evaluation and treatment for neonatal maladjustment syndrome or sepsis. Failure to respond to conventional treatment for these diseases, as well as the characteristic signalment and appearance of these foals, is often sufficiently diagnostic. There is no treatment for LFS, and the prognosis is hopeless for affected individuals.

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

N/A

Contraindications/Possible Interactions!!navigator!!

N/A

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

A lack of response to treatment and recognition of the likely diagnosis based on breed and color should prompt euthanasia in most cases. Genetic testing can confirm the diagnosis antemortem.

Prevention/Avoidance!!navigator!!

Based on the known genetic nature and mode of inheritance of the disorder, it is recommended that genetic testing of Egyptian Arabian breeding stock be performed and carriers removed from breeding programs in an attempt to prevent the disease.

Expected Course and Prognosis!!navigator!!

Affected foals do not recover and invariably die or are euthanized in the hours or days following birth.

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

Mares and stallions that have produced affected foals have also produced foals with juvenile epilepsy. The relationship, if any, between these 2 syndromes is not clear, but they do not appear to occur concurrently.

Abbreviations!!navigator!!

LFS = lavender foal syndrome

Suggested Reading ⬆ ⬇

Brooks SA, Gabreski N, Miller D, et al. Whole-genome SNP association in the horse: identification of a deletion in myosin Va responsible for lavender foal syndrome. PLoS Genet 2010;6(4):e1000909.

Page P, Parker R, Harper C, et al. Clinical, clinicopathologic, postmortem examination findings and familial history of 3 Arabians with lavender foal syndrome. J Vet Intern Med 2006;20:1491–1494.

Author(s) ⬆

Author: Teresa A. Burns

Consulting Editor: Margaret C. Mudge