In dystrophic muscles, intracytoplasmic calcium homeostasis is altered by several mechanisms. One of them involves a defect of the sarcoplasmic ryanodine receptor (RyR1) which leads to excessive leakage of intracellular Ca2 + from the reticulum release. These uncontrolled calcium sparks have been studied in isolated intact muscle fiber from mdx mice and are considered as dystrophic signals. The GRMD dog recapitulates in detail the condition of Duchenne muscular dystrophy patients but to date these signals were not described. Here we present the analysis of calcium sparks in an heterogeneous population of dystrophin-deficient dogs which locomotor phenotype was accurately characterized using a clinical score and several 3D accelerometric parameters. Data were obtained in 22 GRMD dogs. Using predictive markers of the clinical evolution or clinical history, 9 dogs were affected by a severe form (loss of ambulation before the age of 6 months of age) and 13 dogs by a moderate form (no loss of ambulation). Fresh tibialis cranialis muscle biopsies were analyzed for calcium sparks in fourteen 2 month-old dogs, three 4 month-old dogs, seven 6 month-old dogs and in 3 dogs between 12 and 15 month-old. Biopsies from 6 healthy littermates served as controls. All biopsies from GRMD dogs displayed elevated uncontrolled Ca2+ sparks, but the frequency of the events seemed not correlated to the clinical form nor to the age of the dogs. This study shows that leaky RyR1 is a general alteration in dystrophic muscles. Therefore, the pharmacologic inhibition of sarcoplasmic reticulum Ca2 + leak is an additional therapeutic strategic for which the GRMD dog could help to demonstrate its clinical relevance.