Finally, investigation of the transcriptional circuits, which differentiate twins with MS from unaffected twin siblings in the reference nodes of the myeloid compartment, revealed increased expression of FKBP5, CCND3, PER1 and IRAK3 in classical monocytes of twins with MS compared with their unaffected twin siblings (Extended Data Fig. 3f, Supplementary Table 4). Here, PER1 is linked to myeloid sarcoma.