FAMILIAL COMPARISON OF BONE-MINERAL DENSITY AT THE PROXIMAL FEMUR ANDLUMBAR SPINE

Familial resemblance of bone mineral density (BMD) was studied in the lumbar spine and three regions of the proximal femur in 41 biological mother-daughter (M-D), 42 mother-son (M-S), 24 mother-grandmother (M-G ) pairs and 18 mother-grandmother-daughter (M-G-D) triads. Children we re placed into three maturity categories based on an assessment of sec ondary sex characteristics and growth velocities. Two sets of standard ized BMD Z-scores were derived for the children based on either their chronological age or their maturational status. These scores were comp ared with maternal Z-scores derived from age-specific norms. Similar c omparisons were made between the Z-scores of the mothers and grandmoth ers. For all three regions of the proximal femur and for the total AP lumbar spine the correlations between Z-score values were similar and significant (P < 0.05) between the M-G and M-D pairs ranging from 0.41 to 0.57. In general, the familial correlations improved when maturity -status based Z-scores were used for comparison. The absolute BMD valu es measured in the grandmothers and the three maturity groups of the c hildren - expressed as a percentage of the BMD of the mothers - showed that at the neck and the trochanteric regions of the proximal femur t he late-pubescent girls and boys had a significantly (P < 0.05) greate r bone density than their mothers (115-123%), whereas at the AP spine these groups averaged only 88% of their mothers BMD. This site differe ntial was not apparent when comparing the post-menopausal grandmothers with the pre-menopausal mothers (80% at both sites). Three generation comparisons demonstrated a strong familial resemblance in bone minera l density. The value of incorporating maturity-based versus chronologi cal-based parameters for comparison with adult measures in studies tha t involve growing children at different stages of development was also demonstrated.