In this study, we used targeted NGS to screen a large and representative series of patients with intra- and extra-medullary MM (including pPCL or sPCL) for mutations in BRAF, NRAS and KRAS. We evaluated the relationships between the identified variants and the clinical and biological features of the disease, and determined the transcriptional signature associated with MAPK pathway activation in MM. Here, KRAS is linked to Miyoshi myopathy.