BDNF and fragile X syndrome: In addition, GRIN2B and BDNF had distinct subpopulations of individual FXS patients with protein expression levels 2+ standard deviations outside the average for controls (3 patients in GRIN2B and 2 in BDNF, red boxes), with additional patients between 1 and 2 standard deviations outside average for controls (2 in GRIN2B and 3 in BDNF) (Fig. 5b, c).