Brain and Body

Mirror Images of DNA Could Help Navigate the Human Genome

August 9, 2016 | Erica Tennenhouse

DNA bases
Photo credit: Chris Hammang/Garvan Institute of Medical Research

Sequins could improve medical diagnoses.

Genome sequencing keeps getting cheaper and faster, but the technology is still not perfect. With so much complex information running through a sequencer, it is bound to make a decoding error now and again.

Such errors often arise when a stretch of DNA repeats itself — a phenomenon that takes place in around 50 percent of the genome. Repetitive DNA can consist of short two-letter repeats that sit side-by-side (for example, TATATATATA), or pieces of code that pop up again and again throughout the genome.

The trouble is, when a sequencer tries to make sense of lengthy strings of letters by aligning them to a reference human genome, the repeats can get mismatched, throwing the whole sequence out of whack.

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Now, Australian researchers have developed a technology called ‘sequins’ (short for sequencing spike-ins) that may improve the accuracy of DNA sequencing. As lead developer of the technology, Tim Mercer, of the Garvan Institute of Medical Research, explains to The Science Explorer, a sequin is an artificial stretch of DNA that gets added to a person’s genetic sample before sequencing.

From there, the sequin shadows the person’s DNA through the entire sequencing process, from the wet lab to the computer. It can thus be used as an internal control to reveal how sensitive the sequencing technology is, and how accurately it performs

Sequins are essentially mirror-image reflections of natural DNA sequences. “To design sequins, we typically reverse the sequence of the genome feature we are interested in,” says Mercer. “This mirror sequence then forms a good matched control.”

Because they get added to individual samples, sequins can be used to assess the reliability of a sequencing test on a sample-by-sample basis — something that was not previously possible.

“This is very important in clinical diagnosis, where you want to ensure the accuracy and reliability,” says Mercer, who believes the technology will give doctors a more reliable means of deciding the best course of treatment for their patients.

The sequins technology, which is being made freely available to researchers, has been described in an article published in Nature Methods.

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