Thanks to newborn screening tests, each year nearly 12,000 babies who have a serious or life-threatening disorder are diagnosed in time to be treated. (In fact, one of the criteria that a state typically uses when deciding whether a disease should be included in its screening panel is whether there's an effective and affordable treatment.) All 50 states and the District of Columbia now require that every baby be screened for 21 or more of the 29 disorders on the uniform panel recommended by the American College of Medical Genetics. Parents are probably familiar with cystic fibrosis and sickle cell anemia, but other conditions are so rare that you may never have heard of them. The majority are metabolic disorders, in which babies lack a critical cellular function needed to break down, store, or use vital nutrients. Without those nutrients, babies can suffer seizures, organ failure, and even sudden death. "With many of the diseases we screen for, a baby seems perfectly normal at birth," says Parents advisor Jane Morton, M.D., clinical professor of pediatrics at Stanford University School of Medicine. "By identifying the disease quickly, we can prevent serious problems that could cause irreversible damage to the baby."
Doctors can prescribe drugs or supplements, or make careful modifications to a baby's diet that mean the difference between life and death. For example, with one metabolic disease -- phenylketonuria, or PKU -- babies lack an enzyme that converts the amino acid phenylalanine to another amino acid. As a result, this protein building block rises to toxic levels and can cause mental retardation. But if PKU is diagnosed within days of birth, a child will be put on a special infant formula and, later, a rigorously monitored diet that is low in meat, cheese, and legumes that contain the problematic amino acid.
Even though diseases like PKU are caused by genetic abnormalities, the heel-prick test doesn't actually look for faulty genes. It identifies elevated levels of biochemical markers within the dried spots of a baby's blood that indicate a biological process may not be working quite right. An abnormal result won't provide a definite diagnosis, but means a child should have more specific follow-up tests. When parents pass along faulty genes, they usually don't have symptoms of the disease themselves or know of similar conditions in their genealogy. "In more than 90 percent of cases, an infant's diagnosis comes as a complete surprise to the family," says Amy Gaviglio, a genetic counselor with the Minnesota Department of Health.