Which genetic disorder requires newborn screening specimens shortly after birth and again at two weeks old?

The requirement for newborn screening specimens shortly after birth and again at two weeks old is particularly relevant for phenylketonuria (PKU). PKU is an autosomal recessive genetic disorder caused by a deficiency of the enzyme phenylalanine hydroxylase. Without early detection and dietary intervention, infants with PKU can develop serious complications, including intellectual disability and other neurological issues.

The screening for PKU is typically performed shortly after birth to identify affected individuals early, allowing for the implementation of a special diet low in phenylalanine. A second specimen collected at around two weeks of age is essential because it ensures that accurate results are obtained, particularly after newborns have started digesting proteins from breast milk or formula.

In contrast, while cystic fibrosis and sickle cell anemia are also included in newborn screening panels, their screening protocols differ regarding the timing of follow-up tests. Hemophilia, meanwhile, is usually diagnosed based on clinical findings and family history rather than routine newborn screening.