Final answer:
Phenylketonuria (PKU) is the genetic disorder that requires newborn/neonatal screening (NBS) specimens to be collected shortly after birth and again when the infant is about two weeks old.
Step-by-step explanation:
The genetic disorder that requires newborn/neonatal screening (NBS) specimens to be collected shortly after birth and again when the infant is about two weeks old is phenylketonuria (PKU). PKU is an inherited disorder in which the body cannot break down an amino acid called phenylalanine. If left untreated, phenylalanine can build up in the blood and cause intellectual disability and other health problems. Newborn screening tests for PKU by measuring the level of phenylalanine in the baby's blood. If the initial test is positive, a confirmatory test is done to diagnose PKU.