New genetic cause of intellectual disability potentially uncovered in 'junk DNA'

Scientists have uncovered a rare genetic cause of intellectual disability in a historically overlooked part of the human genome: so-called junk DNA. 

This knowledge could someday help to diagnose some patients with these disorders, the researchers say. 

An intellectual disability is a neurodevelopmental disorder that appears during childhood and is characterized by intellectual difficulties that impact people's learning, practical skills and ability to live independently. Such conditions affect approximately 6.5 million Americans. 

Factors such as complications during birth can trigger intellectual disabilities. However, in most cases, the disorders have an underlying genetic cause. So far, around 1,500 genes have been linked with various intellectual disabilities — but clinicians are still not always able to identify the specific cause of every patient's condition. 

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One possible explanation for this gap in knowledge is that previous approaches for reading DNA have only focused on a tiny portion of it. Specifically, they've looked at the roughly 2% of the genome that codes for proteins, known as coding DNA. About 98% of the genome contains DNA that doesn't code for proteins. This DNA was once considered "junk DNA," but scientists are now discovering that it actually performs critical biological functions.

In a new study, published Friday (May 31) in the journal Nature Medicine, scientists used whole-genome sequencing technology to identify a rare genetic mutation within non-coding DNA that seems to contribute to intellectual disability.