The vast majority of primary disorders (>90%) involve translocations between chromosome 14 (IGH gene, 14q32.33) and chromosomes 4 (FGFR3, MMSET genes, in 15% of MM cases), 11 (CCND1, in 15% MM), 16 (MAF, in 5% MM) and 20 (MAFB, in 1% MM). Here, FGFR3 is linked to Miyoshi myopathy.