His Brother's Keeper: A Story from the Edge of Medicine by Jonathan Weiner HarperCollins, New York, 2004

Stephen Heywood, a six-foot-three carpenter from Boston, was 28 when his motor neurons began to fail. The earliest clue was subtle: he lost his first arm wrestling match in years to his older brother, Jamie. Then he couldn't turn a key in the front door of a house he was restoring. A year later he stumbled and pitched headfirst down a stairway. ALS is nothing if not relentless.

Clearly, a kinship links the author and the Heywood brothers. For one thing, they share eerily similar intellectual roots. Stephen and Jamie's father is a mechanical engineer on the faculty at the Massachusetts Institute of Technology (Jamie also graduated from M.I.T. with a degree from his dad's department). Jerome Weiner, Jonathan's father, is an engineering professor at Brown. In the course of the book, Weiner asks his father about Jamie's extreme makeover from high-tech entrepreneur to guerrilla bioscientist. His father replies by likening genes, DNA and protein to any other system--a pulley, a circuit, an engine. At which point the writer adds drily: if what has broken is nothing but a system made of molecules, engineers try to fix it.

"THE HEYWOODS  mean the whole story to me now," writes author Jonathan Weiner, "an allegory from the edge of medicine. A story to make us ask ourselves questions that we have to ask but do not want to ask. How much of life can we engineer? How much is permitted us? What would you do to save your brother's life?"

I longed to hear more from two voices throughout this otherwise fine and moving book. Over a 25-year career, Robert Brown, the ALS specialist at Harvard Medical School who diagnosed Stephen, has led thousands of patients where no one wants to go: the edge of a cliff looking straight down. His perspective would have balanced Jamie's frantic race for a magic bullet. The other voice I missed was Stephen's. Not his matter-of-fact statements, which do weave through the narrative, but his inner thoughts. Was this omission dictated by Stephen himself or the author's delicacy, I wondered.

The 1990s--officially deemed "The Decade of the Brain"--did yield remarkable new facts about the human nervous system as well as breakthroughs in ways of reengineering cells. What is both poignant and telling is Jamie's (and possibly Weiner's) notion that science might, as a result, rescue ALS victims on a specific timetable. Medical miracles do not obey timetables, even in an era of quantum scientific leaps.