Good news!   

Your horse is clear of myotonia and does not have this gene mutation.   

Your horse cannot pass on this mutation. There are no breeding or performance implications.  

What is myotonia?

Myotonia is a heritable condition that affects the skeletal muscles and causes horses to experience rigid muscle contractions when startled or excited.  

When the horse deliberately contracts its muscles (such as when running in fright) the action of relaxing the muscle is occasionally prolonged, causing the muscle fibers to contract and render the horse immobile.  

Genomic Details

The CLCN1 gene provides instructions for making a protein called a chloride channel. This protein helps to control how muscles tense and relax. Horses with the disease mutation have faulty instructions and cannot relax their muscles after being used.

The mutation that causes myotonia is a switch in one of the four base pairs that make up a DNA molecule. Adenine (A) is replaced by Cytosine (C) changing the CLCN1 gene. Therefore, a horse’s genetic result for myotonia is one of three possibilities:

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

  • A/C: Carrier. Does not have the disease. Carries one gene mutation from one parent. This might be passed to their foal.

  • C/C: Affected. Has the genetic disease. The horse has inherited a gene mutation from each parent. One mutation will be passed to their foal