Given previous evidence of familial predisposition for longevity, we hypothesized that siblings and parents of supercentenarians (age >or= 110 years) were predisposed to survival to very old age and that, relative to their birth cohorts, their relative survival probabilities (RSPs) are even higher than what has been observed for the siblings of centenarians.
Mean age at death conditional upon survival to ages 20 and 50 and survival probabilities from ages 20 and 50 to higher ages were determined for 50 male and 56 female siblings and 54 parents of 29 supercentenarians. These estimates were contrasted with comparable estimates based on birth cohort-specific mortality experience for the United States and Sweden.
Conditional on survival to age 20 years, mean age at death of supercentenarians' siblings was approximately 81 years for men and women. Compared with respective Swedish and U.S. birth cohorts, these estimates were 17%-20% (12-14 years) higher for the brothers and 11%-14% (8-10 years) higher for the sisters. Sisters had a 2.9 times greater probability and brothers had a 4.3 times greater probability of survival from age 20 to age 90. Mothers of supercentenarians had a 5.8 times greater probability of surviving from age 50 to age 90. Fathers also experienced an increased survival probability from age 50 to age 90 of 2.7, but it failed to attain statistical significance.
The RSPs of siblings and mothers of supercentenarians revealed a substantial survival advantage and were most pronounced at the oldest ages. The RSP to age 90 for siblings of supercentenarians was approximately the same as that reported for siblings of centenarians. It is possible that greater RSPs are observed for reaching even higher ages such as 100 years, but a larger sample of supercentenarians and their siblings and parents is needed to investigate this possibility.