Inheritance of recurrent exertional rhabdomyolysis in thoroughbreds.
OBJECTIVE
To develop a diagnostic test for recurrent exertional rhabdomyolysis (RER) in Thoroughbreds that relied on in vitro contracture of muscle biopsy specimens and determine whether the inheritance pattern of RER diagnosed on the basis of this contracture test was consistent with an autosomal dominant trait.


METHODS
Clinical trial.


METHODS
8 adult horses with RER and 16 control adult horses for development of the contracture test; 23 foals for inheritance of RER.


METHODS
External intercostal muscle biopsy specimens from the 24 adult horses were tested for contracture in response to halothane and caffeine, and criteria for a positive test result were determined. These criteria were then applied to results for the 23 foals to determine whether they had RER. Simple segregation analysis was performed to determine whether results were consistent with a dominant pattern of inheritance.


RESULTS
Results of the contracture test were positive for 5 of the 12 colts and 4 of the 11 fillies. Results of segregation analysis were consistent with an auto-. somal dominant pattern of inheritance. Two sires with RER produced colts with RER, supporting the hypothesis that RER had an autosomal, rather than an X-linked, inheritance pattern. In addition, in 1 instance, an unaffected colt was produced by 2 affected parents, which was not consistent with a recessive mode of inheritance.


CONCLUSIONS
Although the expression of the RER trait is influenced by sex, temperament, and diet, among other factors, results from the in vitro muscle contracture test and this breeding trial suggest that RER in Thoroughbreds can be modeled as a genetic trait with an autosomal dominant pattern of inheritance.
Dranchak
Patricia K
PK
Department of Veterinary Biomedical Sciences, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108, USA.
Valberg
Stephanie J
SJ
Onan
Gary W
GW
Gallant
Esther M
EM
MacLeay
Jennifer M
JM
McKenzie
Erica C
EC
De La Corte
Flavio D
FD
Ekenstedt
Kari
K
Mickelson
James R
JR
D018685:Anesthetics, Inhalation / Q000494:pharmacology; D000818:Animals; D001706:Biopsy / Q000662:veterinary; D002110:Caffeine / Q000494:pharmacology; D016022:Case-Control Studies; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D005260:Female; D005799:Genes, Dominant; D006221:Halothane / Q000494:pharmacology; D006734:Horse Diseases / Q000175:diagnosis / Q000235:genetics* / Q000503:physiopathology; D006736:Horses; D008297:Male; D009119:Muscle Contraction / Q000235:genetics / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D010375:Pedigree; D010805:Physical Conditioning, Animal / Q000009:adverse effects; D012008:Recurrence; D012206:Rhabdomyolysis / Q000175:diagnosis / Q000235:genetics / Q000503:physiopathology / Q000662:veterinary*
D018685:Anesthetics, Inhalation; D000697:Central Nervous System Stimulants; D002110:Caffeine; D006221:Halothane