Genome editing technology called CRISPR-CAS9 allows the inexpensive and accurate modification of human DNA in relation to biomedical research. However, an expert claims the technique may not work on the alteration of complex human traits such as intelligence.

Professor Cecile Janssens of the Rollins School of Public Health at Emory University explained that scientists need to take into account what can and cannot be genetically edited in human DNA. She said that for a genetic trait to be modified, two requirements must be met.

First, Janssens said that the traits need to be predominantly determined by DNA. The heritability of the trait must be close to 100 percent.

When heritability is low, non-genetic factors such as education, stress and lifestyle can significantly affect the trait. With that, the trait will less likely be genetically modifiable, she added.

Describing a previous meta-analysis of research on heritability featured in Nature Genetics, Janssens said that only a few traits had an estimated heritability higher than 90 percent. The research found that the heritability of higher-level cognition functions and intelligence was only around 50 percent; heritability of muscle power was at 70 percent; and the heritability of personality and temperament was at 45 percent.

Second, Janssens said the genetic architecture must be clear-cut. She said that traits must be the result of a single mutation or by an interaction between a limited number of mutations to be genetically modifiable.

Diseases such as Duchenne muscular dystrophy and sickle cell disease--a severe blood disorder caused by a single-gene mutation of beta-thalassemia--are future targets for gene editing. Janssens said research using CRISPR may result to discoveries for therapies and potential prevention of above diseases.

Still, the use of CRISPR on single-gene disorders can also lead to unintended DNA modifications, Janssens explained. The alteration of the gene may decrease the risk for a disease, but it may also increase the risk for another disease.

What makes a person intelligent is also not a matter of combining the "right genes" and the "right environment", but of the "right combination" of the two factors, she said.

"The technology is not the limitation for enhancing babies - nature is," concluded Janssens.

Meanwhile, former United Nations Secretary-General Kofi Annan once raised concern over the practice of gene editing.

"The greatest fear is that we may be trying to 'play God,' with unforeseeable consequences, in the end precipitating our own destruction," warned Annan.

Photo : Greg Emmerich | Flickr

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