Environmental factors more important than genetic for vertebral fracture

By Ingrid Grasmo

Individual-specific environmental factors such as lifestyle have a greater influence on vertebral fracture risk than genetic factors, suggest study findings.

A high incidence of vertebral fractures has been reported in Scandinavia relative to the rest of Europe, suggesting that either genetic factors or individual-specific environmental factors are at play. Previous research suggests that vertebral fractures are strongly associated with low bone mineral density, which is linked to genetic predisposition.

"To our knowledge, this is the first study to address the genetic liability and environmental influence on clinical vertebral fracture occurrence," say Helen Wagner (Uppsala University, Sweden) and colleagues.

To investigate the contribution of genetic and individual-specific environmental factors to vertebral fracture predisposition, the researchers identified 1072 vertebral fractures occurring after the age of 50 years using data from the Swedish Twin Registry for 33,432 individuals born during 1896-1944.

Wagner and team found that the relative fracture risk - given the twin partner had a fracture - was 3.56 for monozygotic twins compared with 2.07 for dizygotic twins. Furthermore, the age-adjusted heritability for all vertebral fractures was 0.17, which increased to 0.24 when restricting fracture cases to low-energy causes of injury.

Conversely, individual-specific environmental influences accounted for 70-80% of the total variance in vertebral fracture occurrence, independent of type of model used and gender. These influences were found to be stronger in older (aged 80 years or over) men than in women, with the estimate for men 0.86 versus 0.54 for women.

Further analysis showed that individual-specific environmental influences accounted for one-third of the variance (0.33) in vertebral fracture occurrence before the age of 70 years, while they explained most of the variance (0.83) among those aged 80 years or more.

The team notes that inability of the study to accurately determine all prevalent vertebral fractures among twins could likely result in an exaggerated estimate of individual-specific lifestyle influence and an attenuated estimate of the heritability.

"Individual-specific environmental influences such as lifestyle become more important with increasing age, and it is of importance to identify those environmental factors that cause more fracture cases in Scandinavia than in other European settings," conclude the researchers.

The findings are published in the journal Calcified Tissue International.

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