PECAM1 and Nijmegen breakage syndrome: Populations of lymphocytes identified as CD31+CD45RA+ and CD27+CD45RA+CD197+, were significantly less numerous in NBS patients than in healthy controls, both within the CD4+ (median 6.6 vs. 48.9%, 25 vs. 534 cells/μl p < 0.01, and 11.6 vs. 67.6%, 46 vs. 732 cells/μl, p < 0.01, respectively) and CD8+ cell subset (median 32.7 vs. 59.4%, 73 vs. 400 cells/μl, p < 0.01, and 13.7 vs. 48.6%, 25 vs. 302 cells/μl, p < 0.01, respectively; Figures 3, 4).