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CM Congenital Myotonia

    Test that shows if your pony carries the gene change that makes muscles slow to relax, seen in New Forest...

    €43.05 Incl. VAT

      AboutAbout

      This test shows whether your pony carries the gene change linked to congenital myotonia, an inherited muscle disease. The muscles contract normally but are slow to relax, so an affected pony is stiff and struggles to get up.

      It is meant for New Forest ponies and ponies with New Forest ancestry, before breeding or sale.

      Why test?Why test?

      Breeding. Knowing the result of both parents tells you what each mating can produce.

      Tracing a breeding line. Testing relatives shows how far the variant has spread within a breeding group.

      Buying and selling. The result is objective information you can show a buyer.

      A stiff foal. In a New Forest foal that is stiff, struggles to rise or keeps going down, the result confirms or rules out this cause.

      Clinical signsClinical signs

      Signs are known from one affected foal, a colt that developed normally for the first four to six weeks of life and was examined at seven months.

      • Repeated episodes of going down and struggling to get back up because the muscles were too stiff, becoming more frequent over the months
      • More muscle than other foals of the same age
      • Very straight hind legs that barely bent at the hock, a stiff and unwilling way of going, hind feet that did not always follow the front ones, and easily losing balance
      • Fetlocks that could not be bent by hand, and a neck and body that could barely be moved
      • The eyeball pulling back into the socket, with the third eyelid sliding across for about thirty seconds after the eye was examined
      • Overreacting to anything sudden, such as the stable door opening
      • A changed voice: the whinny ended in a high squeak or a low growl
      • Bright and alert, weak but not uncoordinated; stiffness was the main problem

      None of these signs is unique to congenital myotonia. Your veterinarian makes the diagnosis, using the history, the examination and this result.

      TransmissionTransmission

      Congenital myotonia is recessive. A foal needs one copy from the sire and one from the dam to be affected. The gene is not on a sex chromosome, so colts and fillies are affected equally.

      What each mating can produce:

      • n/n x n/n gives 100% n/n
      • n/n x n/CM gives 50% n/n, 50% n/CM
      • n/n x CM/CM gives 100% n/CM
      • n/CM x n/CM gives 25% n/n, 50% n/CM, 25% CM/CM
      • n/CM x CM/CM gives 50% n/CM, 50% CM/CM
      • CM/CM x CM/CM gives 100% CM/CM
      PreventionPrevention

      There is no cure, so prevention is a breeding decision.

      Breeding. Never mate two carriers. Mate a carrier only with a partner that tested negative, and test every foal. No affected foals are born, though some foals will be carriers. This keeps a valuable line while the variant is bred out. Check your studbook's current rules before registering or licensing a stallion.

      Managing an affected pony. No treatment has been evaluated in the horse. Your veterinarian guides care case by case.

      ResultsResults

      n/n: negative. No copy of the variant. Cannot pass it on.

      n/CM: carrier. One copy. The pony stays healthy. Can pass the variant on.

      CM/CM: affected. Two copies. Linked to congenital myotonia. Passes the variant to every foal.

      SampleSample

      Hair roots: 20 to 40 hairs pulled (not cut) from the mane or tail, with the roots attached. Tape them inside the marked area of the printable sample submission form. Hairs without roots cannot be analysed.

      Blood: 5 mL of whole blood in a K3-EDTA tube, collected by a veterinarian. Label the tube with the horse's name and send it with the submission form.

      Keep samples dry and at room temperature, and do not freeze them. Do not send hair that is wet, mouldy or soiled with bedding or faeces. One sample can be used for several DNA tests ordered together.

      TurnaroundTurnaround

      Standard processing: results within 5 to 10 working days of the sample arriving at the laboratory. Shipping is arranged and paid for by the client, and transit time is not included in the 5 to 10 working days.

      Samples that fail DNA extraction or amplification are repeated at no extra cost, which may add a few working days. We contact you if a new sample is required.

      How it worksHow it works

      🛒 Buy the test: select and buy the test online.

      📧 Receive the instructions: after payment is confirmed, you receive the sample collection instructions by e-mail.

      📄 Complete the form: print and complete the submission form with the animal’s identification.

      ✨ Collect the sample: pull 20 to 40 hair roots with the bulb and stick them in the marked area of the form, or ask your veterinarian to collect blood in a K3-EDTA tube.

      📮 Send it to the laboratory: Equigerminal, S.A., HIESE, Rua da Quinta do Sobreiro, 25, Quinta Vale do Espinhal, 3230-343 Penela, PORTUGAL.

      📊 Receive the report: the certified report is issued as soon as the analysis is validated.

      FAQsFAQs

      At what age can a pony be tested?
      Any age, from newborn foal to adult. The genotype never changes, so one test lasts for life.

      How certain is this variant?
      It rests on a single published case. The affected foal had two copies and its sire and dam one each. The authors call it a probable cause that matched the condition in every animal studied.

      Is it fatal?
      The published report gives no outcome, survival figures or prognosis, so no one can say that it is. What it means for an individual pony is a veterinary judgement.

      Does a negative result mean my pony cannot get stiff muscles?
      No. This test looks only for congenital myotonia. Hyperkalaemic periodic paralysis is a separate condition with its own test, and horses have other muscle diseases with no known gene.

      For ProfessionalsFor Professionals

      Genetic and clinical detail for veterinarians, geneticists and laboratories.

      • Gene / locus: CLCN1 (chloride voltage-gated channel 1, skeletal muscle), ECA4.
      • Variant: D592A (Asp592Ala), missense at a residue conserved across mammals, predicted probably damaging; candidate causal variant (Wijnberg et al., 2012). HGVS (EquCab3.0): NC_009147.3:g.96518592A>C; XM_001915636.4:c.1775A>C; XP_001915671.3:p.(Asp592Ala).
      • Alternative designations: published against GenBank XM_001915636 / XP_001915671 (same numbering as the current RefSeq versions).
      • Variant identifiers: rs5334475185 (EVA); OMIA variant 161.
      • Variant classification: not currently evaluated (ISAG/AVCG, per OMIA).
      • Mechanism: the CLCN1 chloride channel provides most of the resting membrane conductance of the muscle fibre; reduced channel function leaves the fibre firing after contraction, producing myotonia. Human homologue: myotonia congenita; the same gene underlies myotonia in goats, mice and dogs.
      • Variant analysis: three CLCN1 differences were found; two did not segregate with disease and are unlikely to alter protein function. The full-length cDNA of the affected foal showed no other abnormality, which excludes a splicing effect (Wijnberg et al., 2012).
      • Inheritance: autosomal recessive (OMIA code R).
      • Penetrance / expressivity: heterozygous relatives were unaffected (Wijnberg et al., 2012).
      • Breeds with documented carriers or cases: New Forest Pony only (OMIA variant record); absent in 56 horses of 13 other breeds (Wijnberg et al., 2012).
      • Allele / carrier frequencies: no population survey published. In the discovery study (102 animals: affected foal, dam, sire, 22 relatives, 21 unrelated New Forest Ponies, 56 horses of 13 other breeds), the affected foal was the only homozygote and 9 carriers were found, all within one family: eight mares including the dam, and the sire. All traced to one suspected founder stallion, paternal grandsire and maternal great-grandsire of the affected foal; none of the 21 unrelated New Forest Ponies carried it. The authors suggest the variant may be recent and confined to one line (Wijnberg et al., 2012). Not detected in 296 horses with muscle disease tested at a neuromuscular laboratory (Aleman et al., 2022). Family-derived percentages are not breed carrier rates.
      • Clinical / diagnostic notes for veterinarians: in the index case (Utrecht University equine clinic), electromyography showed myotonic discharges in every muscle tested; biopsies of four muscles showed marked variation in fibre diameter without necrosis; hyponatraemia, hypokalaemia, hypomagnesaemia and hypochloraemia with raised calcium and phosphate normalised after an episode; renal function was normal; HYPP genotype was negative. The myotonic EMG pattern is not specific to this disease. Electromyography and muscle biopsy are separate procedures and are not replaced by this test. The discovery authors state that direct genetic testing enables eradication of the disease from the New Forest pony breeding population.

      Key references:

      • Wijnberg ID, Owczarek-Lipska M, Sacchetto R, Mascarello F, Pascoli F, Grunberg W, van der Kolk JH, Drogemuller C (2012). A missense mutation in the skeletal muscle chloride channel 1 (CLCN1) as candidate causal mutation for congenital myotonia in a New Forest pony. Neuromuscul Disord 22:361-367. doi:10.1016/j.nmd.2011.10.001. PMID 22197188.
      • Aleman M, Scalco R, Malvick J, Grahn RA, True A, Bellone RR (2022). Prevalence of genetic mutations in horses with muscle disease from a neuromuscular disease laboratory. J Equine Vet Sci 118:104129. doi:10.1016/j.jevs.2022.104129.

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