TABLE I.

Characteristics of same-sex twins enrolled in the University of Washington Twin Registry

	Men	Women
Characteristic	(n = 1010)	(n = 1758)
Zygosity
Monozygotic, n (%)	736 (72.9)	1266 (72.0)
Dizygotic, n (%)	274 (27.1)	492 (28.0)
Age, mean y (SD)	32.3 (14.1)	33.2 (14.8)
Race-ethnicity, n (%)*
White (non-Hispanic)	880 (87.1)	1528 (86.9)
African American	37 (3.7)	41 (2.3)
Asian–Pacific Islander	42 (4.2)	67 (3.8)
Hispanic	21 (2.1)	62 (3.5)
Native Indian–Alaska Native	8 (0.8)	30 (1.7)
Other	22 (2.2)	30 (1.7)
Physician-diagnosed asthma, n (%)†	112 (11.1)	278 (15.8)
BMI, mean (SD)†	25.1 (4.7)	24.4 (5.1)
BMI, n (%)‡
<20	77 (7.6)	274 (15.6)
20–22.49	253 (25.1)	520 (29.6)
22.5–24.99	239 (23.7)	386 (22.0)
25–27.49 (overweight)	205 (20.3)	234 (13.3)
27.5–29.99 (overweight)	110 (10.9)	96 (5.5)
30–39.99 (obese)	115 (11.4)	222 (12.6)
≥ 40 (obese)	11 (1.1)	26 (1.5)

^*P < .05.

^†P < .001.

^‡P < .0001.