DNA changes as you age?

[snopes]

Comment: Recently, I overheard a discussion about a scientific study that
showed as twins age, their DNA can become different. Is this true?
Theoretical? Is it a "This needs more testing to validate" type of study?

This interests me because it also suggests that our DNA changes as we age.
How would this affect DNA tests for criminals who have been convicted of
crimes many years before? If the DNA test says it's not them, can we now
trust the results?

[Silas Sparkhammer]

I remember reading about the "telomere shortening effect" as DNA is copied and recopied many times.

And, like any reproductive process -- xerox, for instance -- yes, errors will be introduced and will propogate.

(As I understand it, both of these may be involved in the detrimental effects of old age. If our DNA duplicated flawlessly, we might be a lot healthier into our golden years.)

But the idea that these errors would be so profound as to render DNA identification testing invalid is profoundly ignorant. By the time DNA degraded that far, it wouldn't be able to sustain life! You'd be a walking tumor, not a person. (And, as such, quite easily identified by other means.)

Once again, a microgram of truth being distorted into a long ton of nonsense by people who don't grok the real concepts involved.

Silas

[damian]

Not sure if it's related, but an Australian girl switched blood types after a liver transplant.

[James G]

Yeah, Silas has it right. Telomers are the stretches of DNA at the end of a chromosome that slowly shorten as cells undergo replication. They can be 'repaired' by the enzyme telomerase, which is active in the germ line (the cells that give rise to sperm/eggs) which is why the human race hasn't undergone a catastrophic loss of information. Activation of telomerase in non-germ line cells is one of the steps that can be important for the immortalisation of a cell line, and thus can be a key step in the progression to cancer.

Meanwhile other mutations will be occuring at each cell division. However this would be unlikely to affect something like a DNA fingerprint. Furthermore, as the only difference between identical twins is a single cell division this is ultimately less significant than the countless subsequent divisions that occur within a person. Thus aging will no more aid the differentation between two identical twins than it will between your own left and right arms.

[jimmy101_again]

Yes, DNA "ages" and drifts over time. Any population of cells undergoes genetic drift with time. All of the cells in something as complex as a human being have different DNA sequences. The differences aren't all that frequent but there are differences.

There are changes in the telomers as cells age as others have posted.

IIRC, the fidelity of DNA replication is such that when a cell divides there are at least a couple of errors in the new DNA (that is out of ~3 billion total nucleotides).

Besides errors that occur with replication, there are changes in the epi-genome with age. Though these are not generally considered to be changes in the genome they do affect how information is extracted from the genome.

There are many regions of the genome that change radically when a cell terminally differentiates. In some cells, large regions of the genome are lost and cannot be recovered. For example, the T-cell receptor locus and the various antibody locuses are permanently changed in cells which express those genes. It would be impossible to clone a human being with a competent immune system starting from a mature T-cell since too much of the immune specific regions of the genome are missing.

Even though every cell in a human has a distinct genome the differences are so rare that it has no affect on DNA testing. Regions of the genome which change significantly depending on the cell type or cell age are not used for DNA testing purposes in criminal cases.

[RBCal]

Cancer results from acquired mutations as you age. A cell typically needs at least 5 or 6 mutations in tumor suppressors and/or oncogenes to become malignant.

The epigenome is variations in methylation on nucleotides throughout the genome. These are important in gene regulation. More methylation in a gene's promoter leads to decreased gene expression. This is also a common method of mutation in some types of cancer (colon cancer particularly). Typically methylation increases with age.

DNA testing is usally from blood. White blood cells (lymphocytes) contain most of the DNA in blood. Also, DNA testing utilizes a relatively small number of polymorphic markers which are non-coding. These can change in tumor samples but usually not in lymphocytes.