The Chinese scientist who sparked interest and outrage last year by claiming to have used gene-editing techniques on twin sisters might have done something to enhance their intelligence.

He Jiankui has not been seen in public since last November, when he announced he used CRISPR technology to alter the genes of the girls to protect them from infection with the HIV virus carried by their father.  He might have expected congratulations, but the scientific world instead expressed horror and concern, and the Chinese government denounced him before he disappeared from public view.

Mr. He didn't say he intended to make the embryos grow into super human twins.  But he did say he was aware of a study in MIT Technology Review that showed that deleting a gene called CCR5 made laboratory mice smarter.  Scientists suspect it could improve human brain recovery after a stroke, and it could be linked to greater success in school.

But none of that is for certain.  Neurobiologist Alcino Silva of University of California, Los Angeles UCLA says the exact effect that deleting CCR5 could have hasn't been explored.

"The work in mice demonstrates the answer may be yes.  But mice are not people," Dr. Silva told the MIT Technology Review, explaining why such a thing "should not be done".

"We simply don't know what the consequences will be in mucking around.  We are not ready for it yet."