Focusing on IGHD genes that were frequent in both MM types, we noted that the utilization of the IGHD3-10 gene in RF2 was significantly more frequent in IgG MM compared to IgA MM (57.9% versus 33.3%, p-value <0.05), whereas RF3 predominated in cases expressing the IGHD5-12 gene belonging to IgA MM versus IgG MM (63.6% versus 57.1%, p-value <0.05) (Supplemental Table 6). Here, BTK is linked to Miyoshi myopathy.