Table 1. Characteristics of African American participants from the SAPPHIRE and SAGE II cohorts stratified by asthma status*.
| Variable | SAPPHIRE cohort | SAGE II cohort | ||||
|---|---|---|---|---|---|---|
| Participants with asthma (n = 2,828) | Participants without asthma (n = 848) | P-value† | Participants with asthma (n = 823) | Participants without asthma (n = 496) | P-value† | |
| Age (years)–mean ± SD | 36.98 ± 12.12 | 39.60 ± 12.55 | <0.001 | 14.06 ± 3.69 | 15.85 ± 3.71 | < 0.001 |
| Female–no. (%) | 1955 (69.1) | 581 (68.5) | 0.766 | 407 (49.5) | 284 (57.3) | 0.007 |
| African ancestry (%)–mean ± SD‡ | 0.80 ± 0.12 | 0.81 ± 0.12 | 0.226 | 0.79 ± 0.13 | 0.78 ± 0.12 | 0.431 |
| BMI (kg/m2)–mean ± SD | 33.17 ± 9.39 | 31.75 ± 7.89 | <0.001 | -- | -- | -- |
| BMI percentile—mean ± SD§ | -- | -- | -- | 76.39 ± 24.74 | 70.95 ± 27.21 | 0.005 |
| Smoking status–no. (%) | -- | -- | <0.001 | -- | -- | 0.001 |
| Current | 765 (27.1) | 107 (12.6) | -- | 68 (8.3) | 68 (13.7) | -- |
| Past | 322 (11.4) | 98 (11.6) | -- | 1 (0.1) | 2 (0.4) | |
| Never | 1740 (61.5) | 643 (75.8) | -- | 753 (91.6) | 426 (85.9) | -- |
| Percent of predicted FEV1 –mean ± SD|| | 85.14 ± 19.67 | 96.70 ± 15.29 | <0.001 | 99.01 ± 13.79 | 101.64 ± 9.22 | < 0.001 |
| Composite ACT score <20 –no. (%)¶ | 1,580 (55.9) | -- | -- | -- | -- | -- |
| Asthma severity score–mean ± SD** | 1.68 ± 0.85 | -- | -- | -- | -- | -- |
| ICS medication use at baseline–no. (%)†† | 237 (46.3) | -- | -- | 282 (58.51) | -- | -- |
| Mitochondrial copy number–mean ± SD‡‡ | 218.60 ± 58.80 | 200.47 ± 64.95 | <0.001 | 235.99 ± 59.22 | 223.07 ± 61.48 | <0.001 |
| WBC counts (1000/μL)–mean ± SD | 6.68 ± 2.32 | 6.10 ± 1.80 | <0.001 | 6.22 ± 1.98 | 6.20 ± 2.12 | 0.951 |
| Neutrophil counts | 3.70 ± 1.92 | 3.24 ± 1.33 | <0.001 | -- | -- | -- |
| Monocyte counts | 0.46 ± 0.17 | 0.43 ± 0.15 | 0.006 | -- | -- | -- |
| Lymphocyte counts | 2.28 ± 0.80 | 2.26 ± 0.72 | 0.633 | -- | -- | -- |
| Eosinophil counts | 0.21 ± 0.19 | 0.14 ± 0.11 | <0.001 | -- | -- | -- |
| Hemoglobin (g/dL)–mean ± SD | 13.29 ± 1.55 | 13.24 ± 1.40 | 0.492 | -- | -- | -- |
| Platelet count (1000/μL)–mean ± SD | 242.35 ± 67.00 | 242.30 ± 61.09 | 0.985 | -- | -- | -- |
| Mitochondrial haplogroup—no. (%)§§ | -- | -- | 0.429 | -- | -- | 0.735 |
| L0 | 122 (4.3) | 42 (5.0) | -- | 42 (5.1) | 22 (4.4) | -- |
| L1 | 516 (18.2) | 166 (19.6) | -- | 149 (18.1) | 94 (19.0) | -- |
| L2 | 826 (29.2) | 262 (30.9) | -- | 225 (27.3) | 145 (29.2) | -- |
| L3 | 1110 (39.2) | 298 (35.1) | -- | 291 (35.4) | 174 (35.1) | -- |
| L4 | 22 (0.8) | 7 (0.8) | -- | 5 (0.6) | 2 (0.4) | -- |
| M | 45 (1.6) | 11 (1.3) | -- | 17 (2.1) | 10 (2.0) | -- |
| N + R | 187 (6.6) | 62 (7.3) | -- | 94 (11.4) | 49 (9.9) | -- |
| East Eurasian | 48 (1.7) | 13 (1.5) | -- | 32 (3.9) | 17 (3.4) | -- |
| West Eurasian | 141 (5.0) | 40 (4.7) | -- | 61 (7.4) | 27 (5.4) | -- |
SAPPHIRE denotes Study of Asthma Phenotypes and Pharmacogenomic Interactions by Race-ethnicity; SAGE II, Study of African Americans, Asthma, Genes, & Environment II; SD, standard deviation; BMI, body mass index; FEV1, forced expiratory volume at 1 second; ACT, asthma control test; ICS, inhaled corticosteroid; and WBC, white blood cell.
*The SAPPHIRE study sample was restricted to participants aged ≥18 years at enrollment and the SAGE II study samples was restricted to participants aged <20 years at enrollment.
†P-value for the difference between study participants with and without asthma in each cohort.
‡The average proportion of African ancestry among African Americans was estimated using a set of autosomal markers which spanned the nuclear genome.
§Growth charts specific for age and sex (available at http://www.cdc.gov/nccdphp/dnpao/growthcharts/resources/sas.htm) were used to calculate the BMI percentile of SAGE II participants.
||Based on the predictive equations from Hankinson et al. (Am J Respir Crit Care Med. 1999 Jan;159[1]:179–87).
¶Composite ACT scores <20 are considered “uncontrolled” asthma.
**This scoring algorithm, which is based on asthma rescue medication use, was developed by Allen-Ramey et al. (J Manag Care Pharm 2006; 12:310–21). This measure was calculated on the 512 individuals with asthma and available pharmacy claims information.
††This measure was calculated on the 512 individuals with asthma and available pharmacy claims information in SAPPHIRE participants and was based on cross-sectional self-report of use in SAGE II participants.
‡‡The mitochondrial copy number estimate was for whole blood. It was based on the sequencing read depth ratio between mitochondrial and nuclear DNA isolated from blood leukocytes.
§§Number of study individuals with a given mitochondrial haplogroup. As shown in Fig 1, the M haplogroups consist of D, E, C/Z, M7 and other M; the N macrohaplogroups consist of X, A, W, I, and the R sub-macrohaplogroups; and R sub-macrohaplogroups consist of U/K, B, F, HV/H/V, and J/T. Geographical mitochondrial haplogroup assignments were based on those described by Pereira et al. (Am J Hum Genet. 2009; 84:628–40). Haplogroups L0, L1, L2, L3, and L4 are considered to be African; haplogroups B, F, A, D, E, and C/Z are considered to be East Eurasian; and haplogroups U/K, J/T, HV/H/V, I, and W are considered to be West Eurasian.