These mutations, which have been linked to serious conditions in transplant recipients, previously went undetected in this donor population.

Nearly two-thirds of mutations in human cancers are attributable to random errors that occur naturally in healthy, dividing cells during DNA replication, researchers report in the 24 March issue of Science. Though mutations that cause human cancer have traditionally been thought to originate from heredity or environmental sources, these results — grounded in a novel mathematical model based on data from around the world — support a role for so-called "R" or random mutations in driving the disease.