Newborn Metabolic Screening Program
Amino Acid Disorder:
What is it?
Phenylketonuria (PKU) is a hereditary disease that is caused by
the lack of a liver enzyme required to digest phenylalanine. Phenylalanine
is an amino acid that is most commonly found in protein containing
foods such as meat, cow's milk, over the counter infant formulas
(both regular and soy) and breast milk.
The gene defect for phenylketonuria is an autosomal recessive
genetic trait and is unknowingly passed down from generation
to generation. This faulty gene only emerges when two carriers
have children together and pass it to their offspring. For each
pregnancy of two such carriers, there is a 25% chance that the
child will be born with the disease and a 50% chance that the
child will be a carrier for the gene defect. Studies show that
1 of every 11,000 live births will have phenylketonuria.
Newborns affected by PKU usually do not show any signs of the
disease at birth. But within the first few weeks of life they
begin to show neurologic disturbances such as epilepsy. Children
suffering from undiagnosed PKU also may have an unpleasant,
musty smell. It has been shown that almost 90% of affected people
have blond hair and blue eyes. Signs also include skeletal changes
such as a small head, short stature, and flat feet. PKU sufferers
may also have a skin disorder called eczema.
PKU affected children who are not diagnosed and do not eliminate
phenylalanine from the diet, will suffer from irreversible brain
damage and mental retardation. Properly treated individuals
should live a normal, healthy life.
Treatment of PKU is the elimination of phenylalanine from the
diet. Phenylalanine is commonly found in protein containing
foods such as meat. Babies who are diagnosed with PKU must immediately
be put on a special milk/formula substitute. Later in life,
the diet is mainly vegetarian.
PKU affected individuals were allowed to go off diet after approximately
12 years of age. However, physicians now recommend that this
special diet should be followed throughout life. Females affected
by PKU, who become pregnant and have stopped following the appropriate
diet, must return to maintaining the diet through the duration
of all pregnancies. Babies of females with PKU who are not on
diet during pregnancy can be severely malformed and mentally
retarded. However, females who are on diet have normal, healthy