Decreased oxidative phosphorylation and PGAM deficiency in horses suffering from atypical myopathy associated with acquired MADD C.M. Westermann a, ⁎, L. Dorland b , O.P. van Diggelen c , K. Schoonderwoerd c , J. Bierau b , H.R. Waterham d , J.H. van der Kolk a a Department of Equine Sciences, Medicine Section, Faculty of Veterinary Medicine, Yalelaan 114, 3584 CM, Utrecht University, Utrecht, The Netherlands b Department of Clinical Genetics, Laboratory of Inherited Metabolic Diseases, Academic Hospital Maastricht, Maastricht, The Netherlands c Laboratory of Enzyme Diagnostics, Department of Clinical Genetics, Erasmus Medical Centre, Rotterdam, The Netherlands d Laboratory Genetic Metabolic Diseases, Department of Clinical Chemistry, Amsterdam Medical Centre, Amsterdam, The Netherlands abstract article info Article history: Received 21 July 2011 Accepted 21 July 2011 Available online 27 July 2011 Keywords: Atypical myopathy Oxidative phosphorylation Respiratory chain PGAM-deficiency Equine MADD Earlier research on ten horses suffering from the frequently fatal disorder atypical myopathy showed that MADD (multiple acyl-CoA dehydrogenase deficiency) is the biochemical derangement behind atypical myopathy. From five horses that died as a result of this disease and seven healthy control horses, urine and plasma were collected ante mortem and muscle biopsies were obtained immediately post-mortem (2 patients and 7 control horses), to analyse creatine, purine and carbohydrate metabolism as well as oxidative phosphorylation. In patients, the mean creatine concentration in urine was increased 17-fold and the concentration of uric acid approximately 4-fold, compared to controls. The highest degree of depletion of glycogen was observed in the patient with the most severe myopathy clinically. In this patient, glycolysis was more active than in the other patients and controls, which may explain this depletion. One patient demonstrated very low phosphoglycerate mutase (PGAM) activity, less than 10% of reference values. Most respiratory chain complex activity in patients was 20–30% lower than in control horses, complex II activity was 42% lower than normal, and one patient had severely decrease ATP-synthase activity, more than 60% lower than in control horses. General markers for myopathic damage are creatine kinase (CK) and lactic acid in plasma, and creatine and uric acid in urine. To obtain more information about the cause of the myopathy analysis of carbohydrate, lipid and protein metabolism as well as oxidative phosphorylation is advised. This study expands the diagnostic possibilities of equine myopathies. © 2011 Elsevier Inc. All rights reserved. 1. Introduction Equine acquired multiple acyl-Coa dehydrogenase deficiency (equine MADD) is the cause of an acute myopathy, known as atypical myopathy (AM), an often fatal condition affecting grazing horses [1–5]. The disease has been reported since 1939 and has an emerging nature, with the largest outbreak in Europe occurring during the autumn of 2009 and affecting at least 371 horses from 10 different countries with a mortality of 71% [6,7]. Clinical symptoms include muscular weakness, recumbency, sweating and myoglobinuria. Routine plasma biochemical analysis reveals markedly elevated activity of the muscle enzymes creatine kinase (CK), lactate dehydrogenase (LDH) and aspartate amino transferase (ASAT), indicating severe muscle damage [8]. Typical histopathologic lesions are degeneration of type I fibers and accumu- lation of lipid droplets [2]. Based on the characteristic urinary profiles of organic acids (ethylmalonic acid and 2-methylsuccinic acid), glycine conjugates ((iso)valerate, butyrate and hexanoate), predominantly short-chain acylcarnitines (acylgroups less than 10 carbon atoms) and deficiency of multiple dehydrogenases in muscle tissue, equine MADD can be confirmed [4,5]. Particular weather conditions appear to trigger the condition suggesting that an exogenic factor, such as a (myco-)toxin, may play an important role in the aetiology of this disease [8]. In humans MADD is an autosomal recessive inherited disorder. However, this seems to be unlikely in equine atypical myopathy given the epizootic occurrence, the variety of breeds involved, the complete recovery of several horses, the ETF and ETF-QO activities as well as their ratios (ETF/SCHAD and ETF-QO/SCHAD) [4,5]. A recent publication reported a strong suspicion that leaves of the Maple tree (Acer pseudoplatanus) covered with European tar spot (Rhytisma acerinum) are the potential cause of this disorder [9]. Molecular Genetics and Metabolism 104 (2011) 273–278 ⁎ Corresponding author. Fax: + 31 302537970. E-mail address: C.M.Westermann@uu.nl (C.M. Westermann). 1096-7192/$ – see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.ymgme.2011.07.022 Contents lists available at ScienceDirect Molecular Genetics and Metabolism journal homepage: www.elsevier.com/locate/ymgme