Justina Pelletier is a fifteen-year-old girl from Connecticut who was born prematurely and suffers from mitochondrial disease, a little-known and somewhat controversial metabolic disorder. For over a year, she had been treated for this condition, also afflicting her older sister, by Dr. Mark Korson, a well-regarded specialist in metabolic diseases at Tufts Medical Center. Last February, her parents, who had become alarmed when a heavy case of the flu led to a serious deterioration in the child’s condition, brought her to Boston Children’s Hospital. BCH is a teaching hospital for Harvard Medical School. The idea was that while there she...