For example, Sarchielli et al. have indicated that CSF levels of BDNF are significantly higher in persons with migraine disease, CSF levels of NGF and BDNF positively correlate with each other, and BDNF levels in the CSF correlate with number of headache days in each month (although correlation was weaker compared to NGF and headache frequency) but not with headache severity [35, 39]. The gene discussed is NGF; the disease is Headache.