B2M and premenstrual tension: Similar to our previous work (Pyle et al., 2015a), and the work of others (Podlesniy et al., 2013; Varhaug et al., 2017; Leurs et al., 2017), we limited our analysis to samples harbouring <1 copy of a housekeeping gene (B2M) to minimise the perceived contamination of cells or cellular debris in the vCSF; reducing our cohort to 14 PMS cases (38%) and 25 controls (58%).