Everybody was waiting for Rudy. On Tuesday night, Patty and Rick Parker were in their cramped kitchen with their 8-year-old son Ben. Dinner was over. Bedtime was near.

Ben’s twin brother, Sammy, lay on a cot in the narrow hallway just outside the kitchen. Unable to see or speak or control his limbs, he coughed or let out a little moan every now and then. Rick and Patty took turns feeding Sammy, who has cerebral palsy, through a stomach tube. He cooed when they kissed his face or stroked his cheek, and when they cooed back, he opened his mouth into a wide, joyful O.