在遺傳中，基因會發生改變甚至突變，這是我們都知道的�？勺罱�冰島一家研究中心指出，在人的一生中，年齡的增長，環境的變化，營養的變化也會導致基因發生改變。

    Individual human genomes change throughout a person's life influenced by environmental or nutritional factors which may explain why illnesses such as cancer come with age, a study said Tuesday.

    Researchers at Johns Hopkins University found that the so-called epigenetic marks on the sequence of a person's DNA modify over the course of their life and the extent of such changes is similar among family members.

    "We're beginning to see that epigenetics stands at the center of modern medicine because epigenetic changes, unlike DNA sequence which is the same in every cell, can occur as a result of dietary and other environmental exposure," said Andrew Feinberg, professor of molecular biology and genetics at the university.
    
    "Epigenetics might very well play a role in diseases like diabetes, autism and cancer," he added in the study published in the Journal of the American Medical Association.

    The team analyzed the DNA sequences from 600 people taking part in the AGES Reykjavik (雷克雅維克，冰島首都) Study, formerly called the Reykjavik Heart Study in Iceland.

    The participants supplied DNA samples in 1991, and then again between 2002 and 2005.

    Scientists then measured the variations in the levels of methylation (甲基化), which is the main epigenetic modification, in 111 samples. In about a third of cases, the methylation levels had changed over the years.

    "Inappropriate methylation levels can contribute to disease -- too much might turn necessary genes off, too little might turn genes on at the wrong time or in the wrong cell," said Vilmundur Gudnason, professor of cardiovascular (心臟血管的) genetics at the University of Iceland.

    "What we saw was a detectable change over time, which showed us proof of the principle that an individual's epigenetics does change with age," added Daniele Fallin, an associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health.

    Such changes could also be hereditary, which might explain why some families are more affected by certain diseases than others.