Adapted from The Gene Machine: How Genetic Technologies Are Changing the Way We Have Kids—And the Kids We Have, by Bonnie Rochman, by arrangement with Scientific American/Farrar, Straus and Giroux (US), China Renmin University Press (China). Copyright © 2017 by Bonnie Rochman. All rights reserved.

In 2010 in Texas, Jennifer Garcia had a baby, a little brother for her four-year-old son. She named him Cameron. Garcia had opted to do prenatal testing for conditions that included Down syndrome and cystic fibrosis with both boys. The tests came back fine. Once her sons were born, she did not think twice about having their heels pricked in the hospital and the resulting droplets of blood scanned for about 30 diseases that make up the standard newborn-screening test administered to babies born in hospitals throughout the Lone Star State.

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