The Genes That Could Cancel Out a Fatal Diagnosis

When Ludivine Verboogen and Romain Alderweireldt’s third child was born in Belgium in late 2015, they marveled at his long fingers. Perhaps one day he will be a famous pianist, they thought. But soon Ludivine grew worried that her son was not developing as well as his two older sisters had. His muscles seemed weak, and the physiotherapy appointments she was taking him to three times a week didn’t seem to be helping. “A lot of doctors were telling us that he was fine, nothing was wrong with him,” Romain recalled to me.

Ludivine persisted, and shortly before their son was a year old, she and Romain found out that his long fingers and lack of muscle tone had a devastating explanation. He was diagnosed with a disease called Marfan syndrome, which generally involves mutations in a gene that helps build connective tissue in the body. Many people with Marfan are exceptionally tall—Abraham Lincoln, for one, may have had the syndrome—and are at very high risk of a kind of fatal rupture in the heart. Ludivine and Romain learned that...