The study began in 1994 and was originally focused on research into Alzheimer's.
However, it soon became apparent that most centenarians did not have Alzheimer's even though other forms of dementia were common, so it transitioned into finding out why some people can live to 100 and others do not.
Researchers are now investigating more detailed genetic analysis including epigenetics.
A study of gene tests of hundreds of centenarians reported in July 2010 that genetics plays an extremely important role in deciding who reaches that age.
Led by Perls, the study was funded by the National Institute on Aging's Division of Geriatrics and Clinical Gerontology.