Phenylketonuria (fen-ul-KEE-tuh-NUR-ee-uh) is a metabolic
disorder caused by a defect in the enzyme that breaks down the amino acid phenylalanine
More to Know
Phenylalanine is one of the eight amino acids that you can only get from food sources.
Usually, after someone eats, the body breaks down phenylalanine with an enzyme called
phenylalanine hydroxylase (PAH) and uses the resulting products to make proteins.
When people have phenylketonuria (PKU), it means they were born with an inherited
defect in the gene
that controls the production of PAH. This means their bodies can’t break down
Phenylalanine is necessary for normal growth in infants and children and for normal
protein production. However, if too much of it builds up in the body, brain tissue
is affected and mental retardation occurs. Phenylalanine also affects melanin, the
pigment responsible for hair and skin color, so kids with PKU often have fair skin
and hair, and blue eyes.
a musty odor to the breath, skin, or urine due to too much phenylalanine in the
All newborn babies in the United States are required to have their blood tested
for signs of PKU. Treatment for PKU involves following a strict diet that should include
the right balance of vegetables, fruits, grains, and fats. The child’s diet
should be low in phenylalanine; this means no high-protein foods like milk, dairy,
meats, eggs, nuts, soy, and beans. A person with PKU should also avoid the artificial
sweetener aspartame. Special protein supplements may be taken to make up any deficiencies.
The special diet should start as soon as PKU is diagnosed and continue for the rest
of the person’s life.
Keep in Mind
With early diagnosis, close medical monitoring, and strict, lifelong adherence
to the right diet, PKU is treatable. Kids and adults with properly treated PKU can
usually expect a good outcome. With delayed treatment or no treatment, brain damage
and some amount of mental retardation will occur.
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