Race and leukocyte telomere length, S. C. Hunt et al. 453 Fig. 2 Age- and body mass index-adjusted leukocyte telomere length (LTL) in a subset of the Bogalusa Heart Study (BHS) based on terminal restriction fragment lengths, determined by using restriction enzymes HinfI/RsaI and HphI/MnII, and by quantitative polymerase chain reaction. Figure displays results from 72 men and 162 women, equally divided by race. Table 3 Leukocyte telomere parameters in a subset of the Bogalusa Heart Study by race and sex in which leukocyte telomere length (LTL) and telomere repeats were measured using restriction enzymes HinfI/RsaI and HphI/MnII, and by quantitative polymerase chain reaction (qPCR) LTL (HinfI/RsaI) (kb) Unadjusted Age-adjusted Age- and BMI-adjusted LTL (HphI/MnII) (kb) Unadjusted Age-adjusted Age- and BMI-adjusted qPCR LTL (T/S units) Unadjusted Age-adjusted Age- and BMI-adjusted BMI, body mass index. Bogalusa Heart Study Whites Men 7.15 ± 0.13 7.16 ± 0.12 7.14 ± 0.12 5.59 ± 0.13 5.61 ± 0.12 5.58 ± 0.13 2.71 ± 0.08 2.69 ± 0.09 2.68 ± 0.09 Women 7.25 ± 0.08 7.24 ± 0.08 7.20 ± 0.08 5.79 ± 0.08 5.78 ± 0.08 5.74 ± 0.08 2.71 ± 0.05 2.72 ± 0.06 2.70 ± 0.06 African Americans Men 7.80 ± 0.11 7.81 ± 0.12 7.82 ± 0.12 6.07 ± 0.13 6.08 ± 0.12 6.10 ± 0.12 3.01 ± 0.10 2.99 ± 0.08 2.99 ± 0.09 Women 7.91 ± 0.08 7.91 ± 0.08 7.95 ± 0.08 6.32 ± 0.08 6.31 ± 0.08 6.34 ± 0.08 3.05 ± 0.06 3.06 ± 0.06 3.08 ± 0.06 p-value gender 0.4702 0.3878 0.3748 0.0292 0.0637 0.0503 0.7923 0.4788 0.4449 p-value race < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 whites and 260 bp for African Americans. However, no such difference was noted between women and men of both races in the relatively younger BHS cohort (Table 2; Fig. 1). Further details regarding LTL results derived from the HinfI/RsaI digest are summarized in Table 2. In most clinical studies, the restriction enzymes for TRF analysis typically comprise HinfI/RsaI. In principle, longer LTL in African Americans than in whites may arise from race-related poly- morphisms in length or the nearest restriction site proximal to the canonic (TTAGGG) stretch of the telomeric repeats. For this reason we also measured in a subset of the BHS cohort TRF length using the restriction enzymes HphI/MnII. Both restriction enzymes HinfI/RsaI and HphI/MnII yield an admixture of TRFs comprising primarily canonical but also some noncanonical telomere repeats at the proximal region of the telomeres. However, HphI/MnII cut the DNA at TGAGGG and TCAGGG, yielding shorter TRFs than those generated by HinfI/RsaI (Allshire et al., 1989; Baird et al., 2006). This is shown in Fig. 2 and Table 3 (and in Supplementary Fig. S1). In this subset, we also measured telomeric DNA content by quantitative polymerase chain reaction (qPCR) analysis, which strictly quantifies telomere repeats. Regardless of the method used, African Americans displayed longer LTL (or a higher T/S ratio) than whites (Fig. 2; also see Table 3). We note that the qPCR method (Cawthon, 2002) has a higher CV% than the TRF length analysis, which might limit detection of small variation in telomere length (Aviv et al., 2006b). However, given the considerable difference in LTL between African Americans and whites, the qPCR measure- ments confirmed the findings of the TRF length analysis. Interestingly, analysis of the TRF products generated by the HphI/ MnII digest showed a significant sex effect on LTL in the BHS. We also obtained the overall and differential counts of leukocytes and their subsets, including neutrophils, in the majority of participants of the BHS whose telomere parameters were measured (Supplementary Table S1). Although African Americans showed significantly lower leukocyte and neutrophil © 2008 The Authors Journal compilation © Blackwell Publishing Ltd/Anatomical Society of Great Britain and Ireland 2008