Idiopathic hypocalcemia

A lethal idiopathic hypocalcemia was described in 1997 for thoroughbred foals. The affected foals suffer from muscle spasms and seizures within the first weeks of life due to calcium deficiency in the blood. Other manifestations can be a stiff gait and increased sweating. The foals died within a few weeks or were euthanized due to the poor prognosis.
In addition to calcium deficiency, the blood count also shows a magnesium deficiency and an increased phosphate level. The parathormone (PTH), which is produced by the parathyroid, increases normally with calcium deficiency. However, no increased PTH concentration was found in the affected foals.
In 2020, the genetic cause underlying calcium deficiency could be described. A gene variant in the RAPGEF5 gene is associated with a subfunction of the parathyroid gland (hypoparathyroidism). This subfunction in turn causes a reduced PTH production, which causes the calcium deficiency.
This is a recessive hereditary disease, i.e. only animals carrying two copies of the disease-causing gene variant show symptoms.
The gene variant has so far only been described in English thoroughbreds. However, since thoroughbreds are used in breeding of other breeds, further distribution is not excluded.