TABLE 1.
Demographic and clinical characteristics of the study sample1
| MZ twins | DZ twins | Siblings | DZ twins and siblings2 | Entire study sample | |
| Individuals (n) | 1303 | 424 | 9525 | 2966 | 1124 |
| Female sex [n (%)] | 62 (48) | 14 (33) | 468 (49) | 134 (45) | 544 (48) |
| White ethnicity [n (%)] | 118 (91) | 34 (81) | 868 (91) | 258 (87) | 1020 (91) |
| Birth cohort [n (%)] | |||||
| 1 (<1980) | 20 (15) | 0 | 35 (4) | 14 (5) | 55 (5) |
| 2 (1980–1984) | 18 (14) | 2 (5) | 81 (9) | 23 (8) | 101 (9) |
| 3 (1985–1989) | 20 (15) | 6 (14) | 167 (18) | 59 (20) | 193 (17) |
| 4 (1990–1994) | 24 (18) | 8 (19) | 267 (28) | 81 (27) | 299 (27) |
| 5 (1995–1999) | 40 (31) | 8 (19) | 273 (29) | 70 (24) | 321 (29) |
| 6 (>1999) | 8 (6) | 18 (43)7 | 129 (14)7 | 49 (17)7 | 155 (14) |
| Age at CF diagnosis (y) | 0.34 (0–4.44)8 | 0.18 (0.01–2.93) | 0.17 (0–4.96) | 0.21 (0–4.61) | 0.20 (0–4.96) |
| n | 115 | 42 | 738 | 239 | 895 |
| Diagnosis by NBS [n (%)] | |||||
| Yes | 5 (4) | 8 (19) | 56 (6) | 22 (7) | 69 (6) |
| No | 122 (94) | 34 (81) | 750 (79) | 274 (93) | 906 (81) |
| Unknown | 3 (2) | 07 | 146 (15) | 0 | 149 (13) |
| F508del homozygotes [n (%)] | 88 (68) | 18 (43)7 | 513 (54)7 | 154 (52)7 | 619 (55) |
| Pancreatic insufficient [n (%)] | 118 (91) | 42 (100)7 | 850 (89) | 277 (94) | 1010 (90) |
| History of meconium ileus [n (%)] | |||||
| Yes | 30 (23) | 9 (21) | 153 (16) | 51 (17) | 192 (17) |
| No | 97 (75) | 33 (79) | 643 (68) | 245 (83) | 773 (69) |
| Unknown | 3 (2) | 0 | 156 (16) | 0 | 159 (14) |
| Presence of a gastrostomy [n (%)] | |||||
| Yes | 14 (11) | 10 (24) | 120 (13) | 42 (14) | 144 (13) |
| No | 108 (83) | 30 (71) | 636 (67) | 254 (86) | 774 (69) |
| Unknown | 8 (6) | 2 (5)7 | 196 (21) | 0 | 206 (18) |
| FEVq6to10 | 0.61 (0.08–0.98) | 0.66 (0.07–0.93) | 0.60 (0.01–1) | 0.59 (0.04–1) | 0.60 (0.01–1) |
| n | 122 | 42 | 932 | 282 | 1096 |
| Insurance status [n (%)] | |||||
| Private insurance | 61 (47) | 24 (57) | 501 (53) | 158 (53) | 586 (52) |
| Public insurance | 61 (47) | 15 (36) | 393 (41) | 128 (43) | 469 (42) |
| Unknown | 8 (6) | 3 (7) | 58 (6) | 10 (3) | 69 (6) |
| Height-z5to10 | −0.79 (−4.61 to 1.12) | −0.80 (−2.86 to 1.76) | −0.51 (−4.40 to 2.46) | −0.60 (−4.40 to 2.12) | −0.58 (−4.61 to 2.46) |
| Weight-z5to10 | −0.54 (−6.23 to 1.56) | −0.72 (−2.41 to 1.80) | −0.40 (−4.71 to 2.38) | −0.39 (−4.71 to 2.34) | −0.42 (−6.23 to 2.38) |
| BMI-z5to10 | −0.10 (−3.89 to 1.89) | −0.32 (−1.74 to 1.58) | −0.06 (−3.60 to 2.30) | −0.07 (−2.83 to 2.11) | −0.07 (−3.89 to 2.30) |
BMI-z5to10, average BMI z score from 5 to 10 y of age; CF, cystic fibrosis; DZ, dizygous; FEVq6to10, average cystic fibrosis–specific forced expiratory volume in 1 s percentile for all measures obtained from 6 to 10 y of age; Height-z5to10, average height z score from 5 to 10 y of age; MZ, monozygous; NBS, newborn screen; Weight-z5to10, average weight z score from 5 to 10 y of age.
Same-sex DZ twins and siblings with <3 y of difference in age.
Included 61 pairs of MZ twins and 4 families with MZ twins and a sibling.
Included 21 pairs of DZ twins.
Included 431 pairs of siblings, 27 families with 3 siblings, 1 family with 5 siblings, and 4 families with MZ twins and a sibling.
Included 148 pairs.
Compared with MZ twins, P < 0.05 (Fisher's exact test or 2-tailed t test).
Median; range in parentheses (all such values).