We analysed the clinical, histochemical, ultrastructural and genetic data of patients affected by central core disease (CCD) studied during the last 20 years. From a total series of 86 CCD-families, we have identified 46 CCD families with RYR1 mutations (16 autosomal dominant, 8 autosomal recessive, 17 sporadic cases and 5 de novo mutations). Out of the other 40 CCD families, the RyR1 gene was entirely excluded in 7 families, by cDNA sequencing or linkage analysis, indicating a genetic heterogeneity of CCD.