Comparative Neuromuscular Diseases Laboratory
Royal Veterinary College
Royal College Street
London
NW1 0TU
Plant sample testing for Atypical Myopathy – owner Information sheet
Atypical myopathy is an often fatal toxic myopathy that is caused by the ingestion of sycamore
seeds, leaves and/or seedlings. This plant material contains a substance called Hypoglycin A (HGA)
that gets converted to a toxin in the horse’s body.
This toxin blocks crucial metabolic pathways,
preventing energy utilisation in the cells. In the horse,
the muscles involved in breathing and posture are
most commonly affected, but heart muscle can also
be involved. Affected horses are usually at pasture or
graze regularly, which makes the ingestion of seeds
and/or seedlings more likely. Clinical signs are often
insidous, with horses showing colic-like signs and/or
generalised weakness, but they can progress rapidly
over 6-12 hours to muscle tremors, low head carriage, reluctance to move and/or recumbancy. Dark
brown or reddish urine is commonly noticed reflecting the pigments released from damaged muscle.
Horses can die with breathing problems or due to a severe heart problem.
Why is it important to confirm Atypical Myopathy?
There is no current treatment for Atypical Myopathy but there are several therapies that have
shown promising results in other animal species affected by this intoxication. Confirmation of the
presence of HGA and its toxic metabolite (MCPA-carnitine) in horse serum is now possible at the RVC
Comparative Neuromuscular Diseases Laboratory: the test can be used in horses suspected of
Atypical Myopathy but also in apparently healthy co-grazers to determine whether they too have
ingested the toxin. If so, preventive therapy could be established earlier which might help avoid the
severe, or fatal consequencies of this disease. These tests should be ordered by your vet after
collection of a blood sample.
There are trees in my pasture but I am not sure whether they are sycamores
Sycamores belong to a large tree family called Acer. There are more than 25 different species in this
family and not all of them have HGA toxin. Differentiation between species is usually based on the
appearance of seeds and leaves but it can be challenging. Several Acer species are present in the UK
-some of them are native such us the field maple (A. campestre), and others have become
naturalised over centuries such as the sycamore (A. pseudoplatanus). The Norway maple (A.
platanoides) and most recently those used for ornamental purposes such as A. palmatum and A.
japonicum are also found. In our pastures, A. campestre and A. platanoides are harmless for horses
as their seeds do not contain HGA. A. psedoplatanus (sycamore) has been shown to have variable
amounts of HGA in its seeds, seedlings and leaves although the factors that result in the variation are
largely unknown. The seeds of the Acer trees are sometimes called “helicopters” as they rotate
rapidly as they fall, due to their special shape: this allows
the seed to be dispersed by the wind. Consequently,
even if you do not have sycamore trees on or at the
boundries of your horse’s pasture, remain vigilant,
particularly in autumn and after strong winds, as some
seeds can reach your pasture when trees are up to 200
yards away. If you want to know whether the
seeds/leaves/seedlings present in your pastures are
potentially harmful for your horse, the Comparative
Neuromuscular Diseases Laboratory at the Royal Veterinary College is offering now a test to detect
HGA in seeds, leaves and seedlings.
How should I take and send the samples?
When collecting samples from the tree, take seeds and/or leaves, ideally from at least 3 branches. If
you collect seeds from the ground or seedlings, divide your pasture in 4 quadrants (4 quarters) and
take samples from each of them (if they are widely scattered) or take them from the area where the
seeds have dispersed. This will allow you to have a representative result for your tree or pasture.
Plant samples should be collected in sealable plastic bags (e.g. sandwich bags) and sent as soon as
possible to the laboratory using the address label that is found on our website; include the plant
material submission form with the samples. The amount of material will depend on the amount
available in your pasture but in generally we recommend:
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A double handfuls of seeds ( approx. 20g)
10 leaves collected from different branches or the ground
One handful of seedlings (approx. 10g).
Results are available in 2-4 weeks following submission. If you require a more rapid
turnaround we do offer an expedited service (at higher cost); please see our website for details.
Please note that the laboratory is unable to discuss specific results with you: instead, we strongly
recommend that you contact your vet for advice. Also please note that if you suspect your horse has
atypical myopathy, or you have concerns, you must contact your vet immediately.
Further details and prices can be found on the lab website.