Table 2. Gene–gene interaction analysis of serum ALP levels followed by analysis of variance.

	Estimate	s.e.	t value	P value (>|t|)
(A) Linear multiple regression
(Intercept)	5.314	0.0375	141.52	<2.00×10−16
Age	0.002	0.0004	3.82	1.35×10−04
Sex	−0.179	0.0099	−18.18	<2.00×10−16
BMI	0.007	0.0015	4.58	4.83×10−06
rs550057	−0.241	0.0138	−17.54	<2.00×10−16
rs2071699	−0.063	0.0094	−6.72	2.10×1011
rs550057:rs2071699	0.045	0.0133	3.37	7.64×10−04

	Degree of freedom	Sum of squares	Mean squares	F value	P value (>F)	Variance explained
(B) Analysis of variance
Age	1	3.41	3.41	53.6	3.14×10−13	0.013
Sex	1	28.41	28.41	446.4	<2.20×10−16	0.110
BMI	1	1.32	1.32	20.7	5.49×10−06	0.005
rs550057	1	31.80	31.80	499.6	<2.20×10−16	0.124
rs2071699	1	2.39	2.39	37.5	1.02×10−09	0.009
rs550057:rs2071699	1	0.72	0.72	11.4	7.64×10−04	0.003
Residuals	2,976	189.41	0.06	—	—	0.736

Abbreviations: ALP, alkaline phosphatase; BMI, body mass index.

(A) Regression analysis of log-transformed serum ALP levels with the covariates age, sex, BMI, rs550057, rs2071699 and the interaction term between rs550057 and rs2071699 (as shown as rs550057:rs2071699). The mode of inheritance was assumed as T-allele dominant for rs550057 and as an additive for rs2071699.

(B) The explained variance was calculated as the proportion of the variance of the log-transformed serum ALP levels divided by the variable.