Quantitative genetic analysis of circulating levels of biochemical markers of bone formation

Carboxyterminal propeptide of type 1 collagen (PICP) and bone Gla-protein-osteocalcin (BGP) are the most important components of the organic bone matrix and play a key role in bone formation. To investigate whether and to what extent variation of the plasma levels of these indices of bone turnover depends on genetic factors, we studied 355 adults belonging to nuclear pedigrees. Genetic analysis was carried out in 2 steps: 1) variance decomposition analysis was performed using the FISHER statistical package; and 2) complex segregation analysis implemented in the program package MAN. The effect of age and gender differences, gender hormones, as well as PTH and vitamin-D (calcidiol) plasma levels were evaluated simultaneously with the parameters of variance analysis. The results showed that about 50% of PICP variation is attributable to genetic factors. The effect of age was significant among men and postmenopausal women, whereas calcidiol influenced variation of PICP in premenopausal women. The results of variance analysis showed that some 40% of BGP, adjusted for confounding variables, can be explained in genetic factors. Age and PTH were important covariates for osteocalcin in men and premenopausal women. Exploration of the maximum likelihood estimates of the various hypotheses concerning the mode of intergenerational transmission of PICP and BGP demonstrated a good correspondence to the Mendelian mode of inheritance (i.e., major gene effect).