Our overall comparably higher ccf-mtDNA levels could be attributed to the increased autolysis or pleoctytosis which occurs in post-mortem CSF (Morris et al., 2012; Bardale, 2009), however we observed a significant reduction in ccf-mtDNA copies in PMS cases, despite no significant difference in PMI, brain weight or B2M levels between PMS cases and controls and no correlation between ccf-mtDNA and ccf-B2M levels, suggesting that this is not the case. The gene discussed is B2M; the disease is premenstrual tension.