Neuro-muscular

Question 1

What is HYPP ?

Answer 1

Hyperkalemic Periodic Paralysis
Genetic disease affecting QH and related breeds, due to a defect in the Na+ channel (SCN4A)
Autosomal dominant with incomplete penetrance.
Major increase in the plasma [K+] until 9.0 mmol/L
Clinical signs : weakness, sweating, muscle fasciculations, prolapse of the 3rd eyelid

Question 2

DDX congenital neurologic disorders in foals

Answer 2

• Hydrocephalus (Friesian)
• Occipitoatlantoaxial malformation (Arabian)
• Cerebellar abiotrophy (Arabian) → autosomal recessive trait, generally detectable between 4 weeks to 6 months of age.
• Juvenile idiopathic epilepsy (JIE) (Arabian of Egyptian lineage) → self-limiting and resolves by 1 to 2 years of age.
• Narcolepsy and cataplexy (familial component)

Question 3

DDX of inherited muscular disorders in foals

Answer 3

• PSSM : QH, Paint, Appaloosa, Draft, WB… Incompletely penetrant autosomal dominant mutation → GYS1 gene. Subclinical in foals.
• Glycogen branchong enzyme deficiency : important cause of stillbirth or early neonatal death in QH and Paint. Autosomal recessive mutation of GBE1 gene → severe impairment of glucose homeostasis.

Question 4

A 24-hour-old Arabian foal of Egyptian lineage is presented in emergency with convulsive neurological disorders. What is your diagnostic hypothesis?

Answer 4

• Lavender foal syndrome (LFS) is a rare inherited lethal disorder occurring in Arabian horses, particularly those of the Egyptian bloodline but also described in other bloodlines.
• The phenotype of a homozygous recessive foal is marked by silver, pale pink or lavender coat colour, hence the name of the disease, also known as coat colour dilution lethal (CCDL).
• The LFS newborn foal exhibits neurological abnormalities such as tetanic seizures with opisthotonic epilepsy, recumbent posture and reluctance to stand for nursing despite the presence of the suckling reflex.

Question 5

Which hereditary disorders are common in Arabian foals ?

Answer 5

• Severe Combined Immunodeficiency disorder (SCID)
• Cerebellar abiotrophy
• Lavender Foal Syndrome (LFS) or Coat Color Dilution Lethal (CCDL)

Question 6

What is the clinical hypothesis of a Thoroughbred foals, presented with neurological tetany and seizures due to hypocalcemia ?

Answer 6

Equine familial isolated hypoparathyroidism (EFIH) : fatal condition in Thoroughbred foals, characterized by muscle contractions and seizures due to hypocalcemia.
Autosomal recessive
Allele frequency in TB → 1.8%