Acknowledgments
We greatly appreciate the time and assistance provided by the centenarians and their family members. We could not have carried out this study without their kind cooperation. This study was partly supported by a grant from the Japanese Ministry of Health and Welfare for the Scientific Research Project on Longevity, a grant for studying the sociomedical background of centenarians (Principal Investigator, Nobuyoshi Hirose), a grant from the Japanese Ministry of Education, Science and Culture (No. 15730346, Yasuyuki Gondo), and aid for research from the Keio Health Consulting Center.

In terms of sampling bias, we also have to mention the young control data. Because of the low frequency of l/l genotype, and not population-based standardized value, we used pooled values as control. This method has the advantage of stabilizing the scattered genotype distribution among small sample studies. However, we could not avoid publication bias, that not all conducted data were published and difficult to control the participants' background. A standardized distribution of 5HTT polymorphism in various age groups with a representative sample must be compared to conform and replicate this finding.