In the heart of Pennsylvania’s Amish country stands a barnlike building that was raised in a day by craftsmen of the “Plain People.” Horses and buggies park out front — and cutting-edge medicine is practiced within. Called the Clinic for Special Children, it focuses on the diseases and genetic mutations that affect one of the most homogenous populations in America: the Amish and Mennonites.

As Philadelphia Inquirer reporter Amy Worden wrote last week, D. Holmes Morton, a Harvard-trained pediatrician, was working at Children’s Hospital of Philadelphia in 1988 when he saw a 6-year-old Amish boy with a disease that had left him brain-damaged and unable to use his limbs.

Some doctors thought he had cerebral palsy. But Morton, who specialized in biochemical genetics, diagnosed glutaric aciduria type 1, or GA1, a metabolic disease that had previously been identified in just eight other humans. The case led him and his wife, Caroline, to found the clinic, which is 25 years old this year.

GA1 is one of 150 diseases or genetic mutations the clinic has identified that disproportionately affect the area’s Amish and Mennonites — a community of 60,000 descended from fewer than 100 settlers who came to Pennsylvania in the 1700s. (Interestingly, the Plain People never get some diseases that are familiar in the general population, including cystic fibrosis and sickle cell anemia.)

Since these diseases and mutations are not exclusive to the Plain People, Morton, and his colleagues are both treating children with special problems and doing genetic research with much broader impact.

D. Holmes Morton founded a clinic after seeing an Amish boy with a disease that had left him brain-damaged and unable to use his limbs. (Daniel Shanken/Associated Press)

Kevin Strauss, the clinic’s medical director, says a more traditional career might have put him in a laboratory “with mice and fruit flies.” Instead, he is a “physician-scientist” in a clinic that identifies five to 10 new gene mutations a year at the same time that it helps a long-underserved community. (Morton, now 63, has been awarded both a MacArthur “genius grant” and the Albert Schweitzer Prize for Humanitarianism.)

“Before 1990, 90 percent of children suffering from GA1 had irreversible brain-damage that left most of them severely disabled,” Worden writes. “Now, if caught early, those with the disease suffer no brain injury and, with vitamins and dietary restrictions, those the clinic treats have been able to live normal lives.”