Bone Abstracts

Differences in fracture rates and bone mass in families and individuals of different ethnic origins may be due to differing lifestyles and/or genetic backgrounds. This study aimed to assess the associations of bone mass and fracture prevalence in adolescents with maternal bone mass and fracture history, and sibling fracture history.

Data from 1389 adolescent-biological mother pairs from the Birth to Twenty (Bt20) longitudinal study were obtained. Questionnaires were completed by adolescents on fractures until 17/18 years of age. Caregivers completed questionnaires on fractures occurring at any age in the adolescent’s sibling/s. Biological mothers completed questionnaires on their own fractures prior to the age of 18 years. Anthropometric and bone mass data on adolescents-biological mother pairs was collected.

White adolescents reported more than double the fracture prevalence of that of other ethnic groups (white (W): 42% vs black (B): 20% and mixed ancestry (MA): 20%; both P<0.001). White mothers reported a higher prevalence of fractures before the age of 18 years than the other groups (W: 31% vs B: 6%; P<0.001 and MA: 16%; MA>B: P<0.01). An adolescent’s risk of fracture was higher if a sibling had a history of fracture (OR=1.5; 95% CI 1.02–2.21; P≤0.05), and if they were white and male, and decreased with increasing maternal lumbar spine BMC (24% reduction in fracture risk for every unit increase in maternal BMC Z-score). Adolescent height, maternal bone area (BA) and bone mineral content (BMC), and white ethnicity were positive predictors for adolescents’ bone mass.

In conclusion we had demonstrated firstly, a strong familial component in fracture patterns among South African adolescents and their siblings, and secondly a significant influence of maternal bone mass on their adolescents’ fracture rates; a novel finding across all ethnic groups.