Given the links between MS progression and mitochondrial DNA (Campbell et al., 2011; Campbell and Mahad, 2018) and previous evidence linking ccf-mtDNA to other neurodegenerative diseases (Pyle et al., 2015a; Podlesniy et al., 2013), we analysed the ccf-mtDNA present in the post mortem ventricular CSF (vCSF) of PMS cases where neurodegeneration is more pronounced, comparing both ccf-mtDNA abundance and integrity to matched controls. Here, PITX1 is linked to premenstrual tension.