A glycogen synthase 1 mutation associated with equine polysaccharide storage myopathy and exertional rhabdomyolysis occurs in a variety of UK breeds.
BACKGROUND
A glycogen synthase (GYS1) mutation has been described in horses with histopathological evidence of polysaccharide storage myopathy (PSSM) in the USA. It is unknown whether the same mutation is present in horses from the UK.


OBJECTIVE
To determine whether the GYS1 mutation occurs in UK horses with histopathological evidence of PSSM and exertional rhabdomyolysis.


OBJECTIVE
The R309H GYS1 mutation is present in a variety of UK horse breeds and that the mutation is commonly associated with exertional rhabdomyolysis.


METHODS
DNA was extracted from 47 muscle or blood samples from UK horses with histories of exertional rhabdomyolysis in which muscle biopsy diagnosis had been pursued. The proportions of GYS1 mutation positive cases were compared among histopathologically defined groups. In addition, breeds that carried the GYS1 mutation were identified from a total of 37 grade 2 (amylase-resistant) PSSM cases.


RESULTS
Of 47 horses with exertional rhabdomyolysis in which a muscle biopsy diagnosis was pursued, 10 (21%) carried the GYS1 mutation. The mutation was only found in horses with grade 2 PSSM (i.e. not in horses with normal, idiopathic myopathy or grade 1 PSSM biopsy samples). In total, the GYS1 mutation was found in 24/37 (65%) of grade 2 PSSM cases. A variety of breeds, including Quarter Horse, Appaloosa, Warmblood, Connemara-cross, Cob, Polo Pony and Thoroughbred cross carried the mutation.


CONCLUSIONS
The GYS1 mutation is an important cause of exertional rhabdomyolysis of UK horse breeds but does not account for all forms of PSSM.


CONCLUSIONS
Genotyping is recommended in cases of exertional rhabdomyolysis, prior to or in combination with, muscle biopsy. However a significant proportion of horses with histopathological evidence of PSSM and/or exertional rhabdomyolysis have different diseases.
Comparative Neuromuscular Diseases Laboratory, Department of Veterinary Clinical Sciences, The Royal Veterinary College, Hawkshead Lane, North Mymms, Hatfield, Hertfordshire AL9 7TA, UK.
R L
RL
Stanley
M E
ME
McCue
S J
SJ
Valberg
J R
JR
Mickelson
I G
IG
Mayhew
C
C
McGowan
C N
CN
Hahn
J C
JC
Patterson-Kane
R J
RJ
Piercy
D000818:Animals; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D020022:Genetic Predisposition to Disease; D006008:Glycogen Storage Disease / Q000235:genetics / Q000378:metabolism / Q000662:veterinary*; D006006:Glycogen Synthase / Q000235:genetics* / Q000378:metabolism; D006734:Horse Diseases / Q000235:genetics*; D006736:Horses; D008297:Male; D018482:Muscle, Skeletal / Q000473:pathology; D011134:Polysaccharides / Q000378:metabolism; D012189:Retrospective Studies; D012206:Rhabdomyolysis / Q000235:genetics / Q000662:veterinary*; D006113:United Kingdom
D011134:Polysaccharides; D006006:Glycogen Synthase