Heritability of recurrent exertional rhabdomyolysis in Thoroughbred racehorses

J. M. MacLeay From the Departments of Clinical and Population Sciences (MacLeay, Valberg, Santschi) and Veterinary Pathobiology (Mickelson), College of Veterinary Medicine, University of Minnesota, St Paul, MN 55108; the Department of Theoretical Statistics, University of Minnesota, Minneapolis, MN 55455 (Kassube, Geyer); Sorum Veterinary Services, city, CA zip (S. Sorum. M. Sorum).

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S. J. Valberg From the Departments of Clinical and Population Sciences (MacLeay, Valberg, Santschi) and Veterinary Pathobiology (Mickelson), College of Veterinary Medicine, University of Minnesota, St Paul, MN 55108; the Department of Theoretical Statistics, University of Minnesota, Minneapolis, MN 55455 (Kassube, Geyer); Sorum Veterinary Services, city, CA zip (S. Sorum. M. Sorum).

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S. A. Sorum From the Departments of Clinical and Population Sciences (MacLeay, Valberg, Santschi) and Veterinary Pathobiology (Mickelson), College of Veterinary Medicine, University of Minnesota, St Paul, MN 55108; the Department of Theoretical Statistics, University of Minnesota, Minneapolis, MN 55455 (Kassube, Geyer); Sorum Veterinary Services, city, CA zip (S. Sorum. M. Sorum).

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M. D. Sorum From the Departments of Clinical and Population Sciences (MacLeay, Valberg, Santschi) and Veterinary Pathobiology (Mickelson), College of Veterinary Medicine, University of Minnesota, St Paul, MN 55108; the Department of Theoretical Statistics, University of Minnesota, Minneapolis, MN 55455 (Kassube, Geyer); Sorum Veterinary Services, city, CA zip (S. Sorum. M. Sorum).

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T. Kassube From the Departments of Clinical and Population Sciences (MacLeay, Valberg, Santschi) and Veterinary Pathobiology (Mickelson), College of Veterinary Medicine, University of Minnesota, St Paul, MN 55108; the Department of Theoretical Statistics, University of Minnesota, Minneapolis, MN 55455 (Kassube, Geyer); Sorum Veterinary Services, city, CA zip (S. Sorum. M. Sorum).

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E. M. Santschi From the Departments of Clinical and Population Sciences (MacLeay, Valberg, Santschi) and Veterinary Pathobiology (Mickelson), College of Veterinary Medicine, University of Minnesota, St Paul, MN 55108; the Department of Theoretical Statistics, University of Minnesota, Minneapolis, MN 55455 (Kassube, Geyer); Sorum Veterinary Services, city, CA zip (S. Sorum. M. Sorum).

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J. R. Mickelson From the Departments of Clinical and Population Sciences (MacLeay, Valberg, Santschi) and Veterinary Pathobiology (Mickelson), College of Veterinary Medicine, University of Minnesota, St Paul, MN 55108; the Department of Theoretical Statistics, University of Minnesota, Minneapolis, MN 55455 (Kassube, Geyer); Sorum Veterinary Services, city, CA zip (S. Sorum. M. Sorum).

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C. J. Geyer From the Departments of Clinical and Population Sciences (MacLeay, Valberg, Santschi) and Veterinary Pathobiology (Mickelson), College of Veterinary Medicine, University of Minnesota, St Paul, MN 55108; the Department of Theoretical Statistics, University of Minnesota, Minneapolis, MN 55455 (Kassube, Geyer); Sorum Veterinary Services, city, CA zip (S. Sorum. M. Sorum).

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Abstract

Objective

To determine the likely mode of inheritance and identify probable foundation horses for recurrent exertional rhabdomyolysis (RER) in Thoroughbred (TB) racehorses.

Animals

4 families of TB racehorses with a high prevalence of RER, consisting of 3 to 53 horses/family, were used to determine mode of inheritance. Sixty-two TB horses with RER and 34 control TB racehorses without RER were used to identify probable foundation horses for the RER trait.

Procedure

RER was diagnosed by a veterinarian and verified by detecting high serum creatine kinase activity. Pedigrees dating from 1930 for all horses were entered into a database. Pedigrees of horses in 4 families were visually inspected for a pattern of inheritance and used for calculation of foundation horse contributions and inbreeding coefficients. The Markov chain Monte Carlo technique was used to analyze pedigrees of the 62 affected and 34 control horses for the conditional probability of foundation genotypes. A dominant mode of inheritance with variable expression model was used.

Results

Pedigree analysis supported an autosomal dominant mode of inheritance with variable expression. All affected horses from the 4 families shared a common ancestor. This ancestor and 5 other stallions had a conditional probability of 1.00 for being affected. All 6 stallions shared a common male ancestor within 3 to 5 generations.

Conclusions and Clinical Relevance

On the basis of this study, the RER trait has been in TB racehorses for more than 70 years and may be inherited as an autosomal dominant trait with variable expression. (Am J Vet Res 1999;60:250–256)

Abstract

Objective

To determine the likely mode of inheritance and identify probable foundation horses for recurrent exertional rhabdomyolysis (RER) in Thoroughbred (TB) racehorses.

Animals

4 families of TB racehorses with a high prevalence of RER, consisting of 3 to 53 horses/family, were used to determine mode of inheritance. Sixty-two TB horses with RER and 34 control TB racehorses without RER were used to identify probable foundation horses for the RER trait.

Procedure

RER was diagnosed by a veterinarian and verified by detecting high serum creatine kinase activity. Pedigrees dating from 1930 for all horses were entered into a database. Pedigrees of horses in 4 families were visually inspected for a pattern of inheritance and used for calculation of foundation horse contributions and inbreeding coefficients. The Markov chain Monte Carlo technique was used to analyze pedigrees of the 62 affected and 34 control horses for the conditional probability of foundation genotypes. A dominant mode of inheritance with variable expression model was used.

Results

Pedigree analysis supported an autosomal dominant mode of inheritance with variable expression. All affected horses from the 4 families shared a common ancestor. This ancestor and 5 other stallions had a conditional probability of 1.00 for being affected. All 6 stallions shared a common male ancestor within 3 to 5 generations.

Conclusions and Clinical Relevance

On the basis of this study, the RER trait has been in TB racehorses for more than 70 years and may be inherited as an autosomal dominant trait with variable expression. (Am J Vet Res 1999;60:250–256)

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