Equine familial isolated hypoparathyroidism

Carrier

Your horse has ONE equine familial isolated hypoparathyroidism gene mutation.

This means that your horse does not have the disease but is a carrier of the mutation.

Breeding implications

Horses with just one gene mutation are clinically unaffected and can live normal lives without any limitations on performance.

If you breed your horse with a mate that does not have the equine familial isolated hypoparathyroidism mutation, there is:

  • A 50% chance the foal will not have this mutation.
  • A 50% chance the foal will have one gene mutation and be disease free, like your horse.

If you choose to breed your horse with another horse that also has one mutation, there is:

  • A 25% chance the foal will not have this mutation.
  • A 50% chance the foal will have one gene mutation and be disease free, like your horse.
  • A 25% chance the foal will have the disease.

If you breed your horse with a mate that is affected with this disease, there is:

  • A 50% chance the foal will have one gene mutation and be disease free, like your horse.
  • A 50% chance the foal will have the disease.
What is equine familial isolated hypoparathyroidism?

Previously known as idiopathic hypocalcaemia, this inherited syndrome affects foals up to 5 weeks of age and causes hypocalcaemia (low blood calcium). Foals affected by this disease have undeveloped or non-existent parathyroid glands, leading to a deficiency in parathyroid hormones and an inability to maintain blood calcium levels. Affected foals don’t respond to oral supplementation of calcium and will either die or be humanely euthanized after prognosis. The disease is not contagious and there are ways to prevent it through responsible breeding practices.

What are the symptoms?
  • Frequent and watery bowel movements.
  • Muscle rigidity and contractions.
  • Bouts of circling.
  • A stilted gait with head and neck extended.
  • Seizure-like activity.
  • High fever.
  • Tachycardia (an unusually fast pulse).
How is it inherited?

Equine familial isolated hypoparathyroidism is a recessive condition, which means your horse must have two copies of the gene mutation to be affected. However, as your horse has only one copy of the disease gene, it is called a carrier, without having the disease.

Genomic Details

Equine familial isolated hypoparathyroidism is associated with a gene mutation in the RAPGEF5 gene. It is not currently known how this gene causes the disease. However, the RAPGEF5 gene regulates a protein called beta-catenin that is important for foal growth and development. This gene also expresses in parathyroid tissue.

The mutation that causes equine familial isolated hypoparathyroidism is a switch in one of the four base pairs that make up a DNA molecule. Cytosine (C) is replaced by Adenine (A) changing the RAPGEF5 gene. Therefore, a horse’s genetic result for equine familial isolated hypoparathyroidism is one of three possibilities:

  • C/C: Normal. Does not have the disease. Does not have the mutation.

  • C/A: Carrier. Has one disease mutation from one parent. This is enough to cause the disease. It might be passed to their foal.

  • A/A: Affected. Has two disease gene mutations, one from each parent. One mutation will be passed to their foal.