Table 1. CYB561 3'-UTR variant A+1485G (rs3087776): Effect on heritable stress heart rate traits in twins and sibs.

Heritability (h²) and genetic covariance were estimated from variance components in twin pairs (MZ versus DZ), with SOLAR. Significance was estimated by MERLIN in twins and sibs, while descriptive statistics were computed by GEE in SAS.

1a. Change in heart rate (HR, beats/min) during cold stress (n=576). Bold: p<0.05.
Trait	Value (beats/min)	Change from basal (p-value).
Basal/resting HR	72.0±0.50	-
Post-stress HR	75.4±0.53	-
Delta (pre→post) HR	3.2±0.39	p=1.92E-13

1b. Heart rate (HR) traits in twin pairs: Heritability and shared genetic determination (pleiotropy).
Heart rate (HR) trait (beats/min)	Trait heritability (h^2) in twins (n=384)			Correlation with basal HR		Shared genetic determination (pleiotropy) with basal HR			Shared environmental determination with basal HR
				Spearman
	h^2	SEM	P-value	ρ	P-value	Rho_G	SEM	P-value	Rho_E	SEM	P-value
Basal/resting HR	0.509	0.064	2.47E-10	-	-	-	-	-	-	-	-
During-stress HR	0.551	0.059	8.79E-13	0.682	2.73E-75	0.747	0.058	2.85E-09	0.603	0.055	8.61E-16
Delta (pre→during) HR	0.407	0.069	1.00E-07	−0.299	1.94E-13	−0.265	0.122	0.056	−0.443	0.068	2.46E-08

1c. Effects of CYB561 3'-UTR variant on HR traits.
Category/Trait	3’-UTR A+1485G diploid genotype (n=576)			P-value
	A/A(122)	A/G (289)	G/G (165)
Heart rate, beats/min
Before environmental (cold) stress	70.0±1.2	72.6±0.8	73.1±1.1	0.010
During environmental (cold) stress	72.0±1.3	76.4±0.8	75.7±1.2	0.002

Bold: p<0.05. “()”: n.

Heritability (h^2), Rho_G, and Rho_E were estimated from twin pair (MZ versus DZ) variance components in SOLAR. Bold: p<0.05.

Model: A_allele recessive; covariates: age, sex, ancestry. Bold: p<0.05.