The genetic influence on fracture susceptibility depends on the type of fracture and age at the time of the event, results from a large Swedish twin study suggest.
In addition, the heritability of osteoporotic fractures is stronger than has been previously estimated, especially for early-occurring osteoporotic fractures, according to the study's lead author, Karl Michaëlsson, M.D., Ph.D., of the Uppsala (Sweden) University Hospital and associates.
The investigators identified 33,432 twins born from 1896 to 1944 included in the Swedish Twin Registry, currently the largest twin registry in the world.
Among them, 24,598 agreed to take part in the study.
Computer-assisted telephone interviews and the Swedish Inpatient Registry were used to identify 6,021 twins with any fracture, 3,599 with osteoporotic fractures, and 1,055 with a hip fracture after the age of 50 years.
Just 16% of the overall age-adjusted fracture variance and 27% of the osteoporotic age-adjusted fracture variance were explained by genetic variation (Arch. Intern. Med. 2005;165:1825–30).
The strongest genetic influence was evident for hip fractures. Nearly half (48%) of the variance in liability to these fractures was attributable to genetic factors.
There was a tendency toward lower heritability estimates of fractures among the men, but it was not statistically significant.
If the first hip fracture within a twin pair occurred before age 69 years, 68% of the variance of liability was explained by genetic factors. If the first hip fracture happened between ages 69 and 79 years, 47% of the variance was attributable to genetic variation. After age 79 years, that figure fell to 3%.
The same pattern of attenuated heredity estimates with increasing age also was evident for the other fracture categories.
“A search for genes and gene-environment interactions that affect early osteoporotic fracture risk is likely to be fruitful, but fracture-prevention efforts at older ages should be focused on lifestyle habits,” the authors report.
Finally, they suggest that an assessment of osteoporotic fracture risk by clinical examination may be recommended for relatives of patients with hip fractures before age 80 years.