Why can your DNA vary from cell to cell? Mosaicism is a ‘hidden mix of mutations’

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Image credit: Art Spot

James Priest couldn’t make sense of it. He was examining the DNA of a desperately ill baby, searching for a genetic mutation that threatened to stop her heart. But the results looked as if they had come from two different infants. “I was just flabbergasted,” said Dr. Priest.

[Astrea Li], it turned out, carried a mixture of genetically distinct cells, a condition known as mosaicism. Some of her cells carried the deadly mutation, but others did not.

[O]ver the course of decades, it has become clear that the genome doesn’t just vary from person to person. It also varies from cell to cell. The condition is not uncommon: We are all mosaics.

When a fertilized egg — known as a zygote — starts dividing in the womb, many of its early descendant cells end up with the wrong number of chromosomes. Some are accidentally duplicated, and others lost. Most of these unbalanced cells divide only slowly or die off altogether, while the normal cells multiply far faster. But a surprising number of embryos survive with some variety in their chromosomes.

Related article:  'Living medicine': Reengineering bacteria to tackle genetic diseases

Astrea underwent transplantation surgery and recovered well enough to go home. She went on to enjoy a normal childhood.

The experience left Dr. Priest wondering how many more people might be at risk from a hidden mix of mutations.

Read full, original post: Every Cell in Your Body Has the Same DNA. Except It Doesn’t

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