Equine multiple acyl-CoA dehydrogenase deficiency (MADD) associated with seasonal pasture myopathy in the midwestern United States.
BACKGROUND
Seasonal pasture myopathy (SPM) is a highly fatal form of nonexertional rhabdomyolysis that occurs in pastured horses in the United States during autumn or spring. In Europe, a similar condition, atypical myopathy (AM), is common. Recently, a defect of lipid metabolism, multiple acyl-CoA dehydrogenase deficiency (MADD), has been identified in horses with AM.


OBJECTIVE
To determine if SPM in the United States is caused by MADD.


METHODS
Six horses diagnosed with SPM based on history, clinical signs, and serum creatine kinase activity, or postmortem findings.


METHODS
Retrospective descriptive study. Submissions to the Neuromuscular Diagnostic Laboratory at the University of Minnesota were reviewed between April 2009 and January 2010 to identify cases of SPM. Inclusion criteria were pastured, presenting with acute nonexertional rhabdomyolysis, and serum, urine, or muscle samples available for analysis. Horses were evaluated for MADD by urine organic acids, serum acylcarnitines, muscle carnitine, or histopathology.


RESULTS
Six horses had clinical signs and, where performed (4/6 horses), postmortem findings consistent with SPM. Affected muscle (4/4) showed degeneration with intramyofiber lipid accumulation, decreased free carnitine concentration, and increased carnitine esters. Serum acylcarnitine profiles (3/3) showed increases in short- and medium-chain acylcarnitines and urinary organic acid profiles (3/3) revealed increased ethylmalonic and methylsuccinic acid levels, and glycine conjugates, consistent with equine MADD.


CONCLUSIONS
Similar to AM, the biochemical defect causing SPM is MADD, which causes defective muscular lipid metabolism and excessive myofiber lipid content. Diagnosis can be made by assessing serum acylcarnitine and urine organic acid profiles.
Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011, USA. beatrice@iastate.edu
B T
BT
Sponseller
S J
SJ
Valberg
N E
NE
Schultz
H
H
Bedford
D M
DM
Wong
K
K
Kersh
G D
GD
Shelton
D000818:Animals; D005260:Female; D006651:Histocytochemistry / Q000662:veterinary; D006734:Horse Diseases / Q000201:enzymology* / Q000209:etiology; D006736:Horses; D008297:Male; D015146:Midwestern United States; D054069:Multiple Acyl Coenzyme A Dehydrogenase Deficiency / Q000097:blood / Q000652:urine / Q000662:veterinary*; D018482:Muscle, Skeletal / Q000201:enzymology*; D012189:Retrospective Studies; D012206:Rhabdomyolysis / Q000201:enzymology / Q000209:etiology / Q000662:veterinary*