Small number of genes causing disorders

Geneticists from Trinity College Dublin have used evolution to work out why a small number of genes can contribute to autism spectrum disorders, schizophrenia, ADHD, intellectual disability, epilepsy and developmental delay.

They made this discovery by observing the genes over time and not as they are today.

There are more than 20,000 genes in the human genome that contain the all-important codes used to produce specific proteins in the body.

The geneticists focused on parts of the genome that are duplicated or deleted in some individuals. They also examined what genes near these places were doing.

Humans all have these duplicates and deletions that vary in size and seem random, but the Trinity team noticed a pattern when they were near a gene associated with a disease condition.

The copies and deletions tended to be longer near these genes but there were less of them, a circumstance that professor in genetics at Trinity, Aoife McLysaght, describes as the “Goldilocks” factor.

Prof McLysaght said: “Our idea was that there must be some genes within these regions with ‘Goldilocks’ properties: too much or too little duplication, and things don’t work properly. The number of copies must be just right.”

The group looked back over our evolutionary history, searching for genes that did not seem to tolerate too much or too little variation. It found that there was far less variation around genes associated with neuro-developmental disorders compared to genes that had no association with disorders.

In their study, the discovered “the genes that matter”.

“These disease-causing regions, within the human genome, contain a vast number of genes and it has been very difficult to identify the specific genes that cause diseases. Our work demonstrates that our evolutionary history is useful for understanding human disease,” it said.

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