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Inheritance of recurrent exertional rhabdomyolysis in Thoroughbreds

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  • 1 Department of Veterinary Biomedical Sciences, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108.
  • | 2 Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108.
  • | 3 Department of Animal and Food Sciences, University of Wisconsin, River Falls, WI 54022.
  • | 4 Department of Veterinary Biomedical Sciences, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108.
  • | 5 Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108.
  • | 6 Present address is the Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523.
  • | 7 Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108.
  • | 8 Present address is Comparative Exercise Physiology Laboratory, College of Veterinary Medicine, Oklahoma State University, Stillwater, OK 74078.
  • | 9 Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108
  • | 10 Present address: Departamento de Clinica de Grandes Animais, Centro de Ciencias Rurais, Universeidada Federal de Santa Maria, Santa Maria, Brazil.
  • | 11 Department of Veterinary Biomedical Sciences, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108.
  • | 12 Department of Veterinary Biomedical Sciences, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108.

Abstract

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.

Design—Clinical trial.

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

Procedure—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 autosomal 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 and Clinical Relevance—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. ( J Am Vet Med Assoc 2005;227:762–767)

Abstract

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.

Design—Clinical trial.

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

Procedure—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 autosomal 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 and Clinical Relevance—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. ( J Am Vet Med Assoc 2005;227:762–767)