Newborn screening debuted as a public health program in the United States in the early 1960s, and has expanded to countries around the world, with different testing menus in each country. Both prenatal screening (screening before birth) and newborn screening (screening soon after birth) have improved health care. The first disorder detected by modern newborn screening programs was phenylketonuria, a metabolic condition in which the inability to degrade the essential amino acid phenylalanine can cause irreversible mental retardation unless detected early.