Detecting Poisons at Birth

In Massachusetts, just before a newborn baby is taken home from the hospital he is given a novel goodby: a doctor takes hold of him and jabs a lancet into his heel. From the resulting tiny puncture, the doctor squeezes three drops of blood, one each into circles printed on a piece of filter paper. With a midget bandage stuck on his heel, the baby is ready to leave. There is still one more formality: the mother gets a leaflet explaining the purpose of the jab in the heel and why she should have it repeated when the baby is a month old.

The Massachusetts department of public health decided a year ago to turn the commonwealth into a proving ground for an all-out attack on an inherited metabolic disorder, phenylketonuria or PKU, which causes severe mental retardation. (At least 5,000 of the 5.5 million mentally retarded in the U.S. are PKU victims.) Because of a defective gene inherited from both parents, a PKU baby cannot make use of phenylalanine, which is found in most protein foods, and the poison that accumulates in his system as a result permanently damages the brain. But if PKU is detected early enough, a special diet will avert nearly all the damage. The difficulty lies in early detection. In the laboratory, the blood spots on the filter paper will reveal PKU.

All maternity services in Massachusetts now do the heel test before discharging a baby. But the child may then be no more than four days old, which is a little too early for PKU to be detected with certainty. Hence the advice to the mother: take the month-old baby to a pediatrician for a second test. In case the mother has no pediatrician, or feels she cannot afford to use one, the health department gives her an alternative. Along with the explanatory leaflet the mother gets some filter paper, with instructions to put a piece inside the baby's diaper. After the wet diaper is removed, the mother dries the paper and mails it to a state laboratory, where chemical analysis will diagnose PKU. This urine test is rated useful, but not quite as reliable as the heel-blood test.

From the first few months of the voluntary plan, its value was clear, and now an act of the General Court of Massachusetts has made testing mandatory. Only a year ago, the frequency of PKU was estimated at one in every 20,000 births. Then authorities began to suspect it might be twice as high. But among the first 40,000 babies tested in Massachusetts, eight cases were detected--an incidence of one in 5,000 births. For the whole U.S., that would be 800 PKU babies a year.

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