Objective: To evaluate calcium deficiency and demand in pre-puberty twins and to analyze the heritability of serum bone alkaline phosphatase (BALP).
Methods: A total of 73 pairs of twins aged 9-16 years were examined by BALP test. Microsatellite polymorphism was used to diagnose the zygosity of twins, while both intraclass correlation coefficient method and Christian formula were performed to investigate heritability of serum BALP.
Results: The results of zygosity diagnosis displayed that 34 pairs of twins were monozygotic (MZ) twins and 39 pairs were dizygotic (DZ) twins. 97.9% of the subjects appeared unusual in the activity of BALP, with activity of BALP > 250 U/L in 43.1% of subjects and 200-250 U/L in 54.8% of the subjects. The intake of calcium was unsatisfied in 48.4% of the boys and 39.0% in girls. Less than 10.0% of the subjects were satisfied with the intake of calcium in each age group while over 45.0% of the subjects in 10-13 age group were deficient in calcium. Differences between the means of BALP in different sex groups (t = 1.633, P = 0.105) and different age groups (F = 0.323, P = 0.924) were not statistically significant. Heritability analysis displayed that intra-class variation, inter-class variation, intra-class correlation coefficient were 191.54, 1462.22, 0.77 in MZ twins, and those were 491.03, 1475.57, 0.50 in DZ twins respectively with the heritability of BALP activity as 0.54.
Conclusion: Calcium deficiency is commonplace in pre-puberty twins. Our data showed that the BALP activity was influenced both by genetic (54%) and environmental (46%) factors.