Short DNA strands key to understanding Alzheimer’s

Short snippets of DNA found in human brain tissue can help understand human cognitive function and risk for developing certain neurological diseases like Alzheimer’s and autism, according to a new study.

Researchers from the Mount Sinai School of Medicine found that many of the sequences with human-specific epigenetic characteristics, until recently, considered to be “junk DNA” – with no particular function – can present new leads on how the human brain has evolved, and a starting point for studying neurological diseases.

There are nearly 40 million positions in the human genome with Deoxyribonucleic acid (DNA) sequences that are different than those in non-human primates, making the task of learning which are important and which are inconsequential a challenge for scientists.

Rather than comparing these sequences strand by strand, wanted to identify the crucial set of differences between the two genomes by looking more broadly at the chromatin, the structure that packages the DNA and controls how it is expressed.

They found hundreds of regions throughout the human genome which showed a markedly different chromatin structure in neurons in the prefrontal cortex, a brain region that controls complex emotional and cognitive behaviour, compared to non-human primates.

“While mapping the human genome has taught us a great deal about human biology, the emerging field of epigenomics may help us identify previously overlooked or discarded sequences that are key to understanding disease,” said Dr Schahram Akbarian.

“We identified hundreds of loci that represent untapped areas of study that may have therapeutic potential,” Akbarian said in a statement.

The team isolated small snippets of chromatin fibres from the prefrontal cortex. Next, they analysed these snippets to determine what genetic signals they were expressing.

For example, the sequence of DPP10-a gene critically important for normal human brain development-not only showed distinct human-specific chromatin structures different from other primate brains such as the chimpanzee or the macaque, but the underlying DNA sequence showed some interesting differences from two extinct primate-the Neanderthal and Denisovan, most closely related to our own species and also referred to as ‘archaic hominines’

“Many neurological disorders are unique to human and are very hard as a clinical syndrome to study in animals, such as Alzheimer’s disease, autism, and depression. By studying epigenetics we can learn more about those unique pieces of the human genome,” said Akbarian.

The findings are published in the journal PLoS Biology.

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