A tale of three sisters offers a glimpse into how, with the right systems in place, genomics research can already be applied to alleviate human suffering.

In January 2007 Jesse and Anna, members of an Old Order Amish settlement in Pennsylvania, brought their daughter Esther to the Clinic for Special Children in Strasburg, Pa. (For privacy, pseudonyms are used for all children mentioned in this article.) Esther, just a few hours old, was born with inflamed skin, patchy hair loss and a swollen liver—telltale signs of Omenn syndrome, a rare and lethal form of severe combined immune deficiency. Our clinic is a shelter for children like Esther, who enter the world facing dangerous genetic risks.

Esther’s sister Mary was born 14 years earlier, in 1993, and lived out a short life of misery marked by infections, needles, ventilators and feeding tubes. She died of pneumonia before a specific diagnosis could be confirmed and left behind a shattered family with more than $400,000 of hospital bills.

Esther’s life would be different. From her first hours, she had a medical home where her care was informed by a deep but pragmatic understanding of biology, culture and the places where they meet. Using advanced molecular techniques, our laboratory director, Erik Puffenberger, rapidly homed in on Esther’s genetic diagnosis (recombination-activating gene 1, RAG1) and proved that her sister Mary succumbed to the same condition. Using these same molecular data, Puffenberger identified an ideal bone marrow transplant donor among Esther’s siblings that enabled her to have a lifesaving transplant at 65 days of age. The entire process—from clinical presentation to genetic diagnosis to donor identification—took less than two weeks, saved the family about $80,000 and cleared the path to a cure.

Severe combined immune deficiency (SCID), first recognized in 1950, encompasses a variety of genetic disorders that render the immune system powerless. Without radical treatment in the form of bone marrow–cell transplant, children with SCID inevitably die from infections by two years of age. In 1972 a paper in The Lancet described the first specific protein deficiency linked to SCID, an enzyme called adenosine deaminase. In the years that followed immunogenetics research advanced at an explosive pace. Doctors today know of 18 different molecular causes of SCID, four of which are found in high prevalence among the Amish and Mennonites of North America (collectively called “Plain” people). And yet as this knowledge unfolded, 26 of 41 (63 percent) Plain children born with SCID died by two years of age because of late diagnosis, geographic and cultural isolation, and unaffordable access to care. It was not the research community but anguished parents—people like Jesse and Anna—who brought this problem to our front door.

Esther is now eight years old and healthy. In May 2013 her baby sister Annie arrived. Using blood from the umbilical cord, we diagnosed Annie with Omenn syndrome at four hours of age for a cost of less than $50. Annie’s father peered anxiously over the shoulders of our laboratory team as they inspected molecular markers to identify a bone marrow donor for this daughter. Annie was successfully transplanted in the first month of life and has thrived ever since.

This tale of three sisters, rising from a community’s tragic history, is a paradigm of how genomics can shape the everyday delivery of medical care. These three Amish sisters give us a peek into the future of genomics, which has the power to make the healing arts preemptive rather than reactive. Progress along this track must be measured one patient at a time, and in terms people understand. For this family, help did not come in the form of new knowledge but from choices made about how to use what we know. Applying molecular tools to the task was not so much an innovative as a sensible thing to do.

Kevin A. Strauss, who earned his MD degree from Harvard Medical School, is the medical director of the Clinic for Special Children, in Strasburg, Pa.