Defects in Metabolism of Amino Acids: PKU One condition that all
newborns in the U.S. are screened for is phenylketonuria (PKU),
a metabolic disorder passed down from both parents. Before the
simple blood test that checks for PKU became routine, the
condition could go undetected long enough to cause severe
intellectual disability. Now the disorder can be diagnosed
before it leads to any damage. What is PKU? PKU is caused by a
defect in a gene known as the PAH gene. This defect changes the
way that the amino acid phenylalanine is broken down by the body
during digestion. Phenylalanine comes from commonly eaten foods.
It helps the body make protein. It is also important for brain
development. It is normally changed to tyrosine, which helps
create all of the body's proteins. Because phenylalanine can't
be properly processed when you have PKU, the amino acid can
build up in the bloodstream and cause harm. Causes of PKU PKU is
passed on to children when both parents have only one mutated
gene. This means that neit