The fluids are rarely preserved, though, and thorough autopsies often are not performed, according to Dr. Piero Rinaldo, a biochemical geneticist at the Mayo Clinic. Dr. Rinaldo spoke at the National Child Abuse Defense and Resource Center's Tenth International Conference in Reno in October. Urine and serum should be gathered before the child recovers, preferably when his condition is at its worst, Dr. Rinaldo said. If the child dies, those same fluids, plus liver and bile specimens, should be gathered at autopsy.

Dr. Rinaldo explained that many physicians who see children with unexplained symptoms give little thought to "inborn errors of metabolism," or IEM, as geneticists call these disorders. In the past forty years the number of IEM known to medical science has grown from 81 to more than one thousand. Practicing physicians can hardly keep up with this explosive growth in medical knowledge, and frequently IEM are either not recognized or misdiagnosed.

Repeated unexplained injuries to a child incline physicians to diagnose child abuse. More than one SIDS death in a family affects them that way, too. Yet these recurrences also suggest a hereditary metabolic disorder, Dr. Rinaldo said.

One IEM, glutaric acidemia type 1, can lead to a subdural hematoma and retinal hemorrhages. These are two symptoms which often underlie a diagnosis of shaken baby syndrome.