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Congenital Myotonia - CM - Equigerminal

Congenital Myotonia - CM

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  • DNA test for the Congenital Myotonia (CM). This test verifies the presence of the recessive cm gene.


  • 30 to 40 hair roots
  • 5 mL of blood in a K3 EDTA tube

Turnaround time

  • 2 to 5  working days

Why test?

  • This genetic test helps breeders to identify horses that carrying the cm recessive mutation. Informed choices can be made for breeding selections, and prevent the born of affected foals.

Results description

The DNA test verifies the presence of the recessive cm gene and presents results as one of the following:

  • N/ - Normal for Congenital Myotonia (CM).  Absence of the affected variant responsible for Congenital Myotonia
  • N/cm Carrier of Congenital Myotonia (CM). Presence of one copy of the genetic variant causative of Congenital Myotonia. The horse is clinical healthy and can pass the genetic variant responsible for CM to 50% of their progeny when bred.
  • cm/ - Affected by CM. Presence of two copies of the genetic variant causative of Congenital Myotonia. The horse is affected with Congenital Myotonia and will pass genetic variant to 100% of its offspring.

Additional information

  • Congenital Myotonia is an inherited neuromuscular disorder characterised by the slow relaxation of muscles after voluntary contraction or electrical stimulation.
  • This disorder has been identified in New Forest ponies and it is caused by an autosomal recessive mutation, which is responsible for the function of chloride ion channels in the skeletal muscle.
  • Carriers of the mutation appear normal, but when two carriers are mated, a 25 percent chance exists that an affected foal will be produced. 
  • Affected foals appear normal at birth. The first symptoms are recurrent episodes of recumbency and difficulty rising to its feet as a result of muscle stiffness. They occur during the first weeks of age and usually increase in the following months.
  • Picking up the limbs is not possible because of the muscle rigidity. The eye-bulb may be retracted due to the myotonia.