Download PKU (Phenylketonuria) in your baby

What is phenylketonuria?
Phenylketonuria (commonly known as PKU) is an inherited disorder that increases the levels of a substance
called phenylalanine in the blood. Phenylalanine is a building block of proteins (an amino acid) that is obtained
through the diet. It is found in all proteins and in some artificial sweeteners. If PKU is not treated, phenylalanine
can build up to harmful levels in the body, causing intellectual disability and other serious health problems.
The signs and symptoms of PKU vary from mild to severe. The most severe form of this disorder is known as
classic PKU. Infants with classic PKU appear normal until they are a few months old. Without treatment, these
children develop permanent intellectual disability. Seizures, delayed development, behavioral problems, and
psychiatric disorders are also common. Untreated individuals may have a musty or mouse-like odor as a side
effect of excess phenylalanine in the body. Children with classic PKU tend to have lighter skin and hair than
unaffected family members and are also likely to have skin disorders such as eczema.
Less severe forms of this condition, sometimes called variant PKU and non-PKU hyperphenylalaninemia, have
a smaller risk of brain damage. People with very mild cases may not require treatment with a low-phenylalanine
diet.
Babies born to mothers with PKU and uncontrolled phenylalanine levels (women who no longer follow a lowphenylalanine diet) have a significant risk of intellectual disability because they are exposed to very high levels
of phenylalanine before birth. These infants may also have a low birth weight and grow more slowly than other
children. Other characteristic medical problems include heart defects or other heart problems, an abnormally
small head size (microcephaly), and behavioral problems. Women with PKU and uncontrolled phenylalanine
levels also have an increased risk of pregnancy loss.
How common is phenylketonuria?
The occurrence of PKU varies among ethnic groups and geographic regions worldwide. In the United States,
PKU occurs in 1 in 10,000 to 15,000 newborns. Most cases of PKU are detected shortly after birth by newborn
screening, and treatment is started promptly. As a result, the severe signs and symptoms of classic PKU are
rarely seen.
What genes are related to phenylketonuria?
Mutations in the PAH gene cause phenylketonuria. The PAH gene provides instructions for making an enzyme
called phenylalanine hydroxylase. This enzyme converts the amino acid phenylalanine to other important
compounds in the body. If gene mutations reduce the activity of phenylalanine hydroxylase, phenylalanine from
the diet is not processed effectively. As a result, this amino acid can build up to toxic levels in the blood and
other tissues. Because nerve cells in the brain are particularly sensitive to phenylalanine levels, excessive
amounts of this substance can cause brain damage.
Classic PKU, the most severe form of the disorder, occurs when phenylalanine hydroxylase activity is severely
reduced or absent. People with untreated classic PKU have levels of phenylalanine high enough to cause severe
brain damage and other serious medical problems. Mutations in the PAH gene that allow the enzyme to retain
some activity result in milder versions of this condition, such as variant PKU or non-PKU
hyperphenylalaninemia. Changes in other genes may influence the severity of PKU, but little is known about
these additional genetic factors.
How do people inherit phenylketonuria?
This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell
have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the
mutated gene, but they typically do not show signs and symptoms of the condition.
PKU (Phenylketonuria) in your baby
Phenylketonuria (also called PKU) is a condition in which your body can’t break down an amino acid called phenylalanine. Amino
acids help build protein in your body. Without treatment, phenylalanine builds up in the blood and causes health problems.
In the United States, about 1 in 10,000 to 15,000 babies is born with PKU each year. The illness happens in all ethnic groups. But it’s
more common in people who are Native American and Northern European than those who are African-American, Ashkenazi Jewish or
Japanese.
What causes PKU?
PKU is inherited. This means it’s passed from parent to child through genes. A gene is a part of your body’s cells that stores
instructions for the way your body grows and works. Genes come in pairs—you get one of each pair from each parent.
Sometimes the instructions in genes change. This is called a gene change or a mutation. Parents can pass gene changes to their
children. Sometimes a gene change can cause a gene to not work correctly. Sometimes it can cause birth defects or other health
conditions. A birth defect is a health condition that is present in a baby at birth.
Your baby has to inherit a gene change for PKU from both parents to have PKU. If she inherits the gene from just one parent, she
has the gene change for PKU, but she doesn’t have PKU. When this happens, your baby is called a PKU carrier. A PKU carrier has the
gene change but doesn’t have PKU.
How do you know if your baby has PKU?
All babies have a newborn screening test for PKU. Newborn screening checks for serious but rare conditions at birth. It includes
blood, hearing and heart screening. With newborn screening, PKU can be found and treated early so babies can grow up healthy.
Before your baby leaves the hospital, his health care provider takes a few drops of blood from his heel. The blood is collected on a
special paper and sent to a lab for testing. The lab then sends the results back to your baby’s provider.
If newborn screening results aren’t normal, it simply means your baby needs more testing. Your baby’s provider can recommend
another kind of test, called a diagnostic test. This test can check to see if your baby has PKU or if there is some other cause for
abnormal test results.
If your baby is tested before he’s a full day old, it’s possible for the test to miss PKU. Some experts recommend that if your baby was
tested within the first 24 hours of life, he should be tested again at 1 to 2 weeks of age.
What problems can PKU cause?
Babies born with PKU seem normal for the first few months of life. But without treatment, they begin to have signs and symptoms of
the illness at about 6 months of age. These include:
 Jerky movements in arms and legs
 Lighter skin and eyes (Babies with PKU can’t properly make melanin, the pigment in the body that’s responsible for
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skin and hair color.)
Musty body smell
Seizures
Skin rashes
Small head size
Taking longer than expected to sit, crawl or walk
Losing interest in surroundings
Delays in mental and social skills
Intellectual disabilities
Behavior problems, like being hyperactive
If your baby has PKU, what kind of treatment does he need?
If your baby has PKU, he may need testing as often as once a week or more often for the first year of life to check his phenylalanine
levels. After that, he may have testing once or twice a month throughout childhood.
Your baby needs to follow a special meal plan that is low in phenylalanine. It’s best to start this meal plan as soon as possible, ideally
within the first 7 to 10 days of life.
At first, your baby gets a special protein formula that has reduced phenylalanine. Protein is important to help your baby grow and
develop. The amount of phylalanine in the formula is controlled to meet you baby’s individual needs. Your baby also can have some
breast milk. Your breast milk has phenylalanine in it, so talk to your baby’s provider to find out how much breast milk your baby can
have.
When your baby is ready to eat solid foods, she can eat vegetables, fruits, some grains (like low-protein cereals, breads and pasta)
and other low-phenylalanine foods. If your baby has PKU, she should not eat:
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Milk, cheese, ice cream and other dairy products
Eggs
Meat and poultry
Fish
Nuts
Beans
 Food or drinks that contain aspartame. This is an artificial sweetener that has lots of phenylalanine in it. It’s sold as
NutraSweet® and Equal®.
PKU meal plans are different for each baby and can vary over time depending on how much phenylalanine your baby can take.
Health care providers at a medical center or clinic that has a special program to treat PKU can help you create a PKU meal plan for
your baby. Ask your baby’s health care provider for information on a medical center or clinic that treats PKU.
Your child follows the PKU meal plan through her whole life. If she eventually gets pregnant, she follows her meal plan throughout
pregnancy. Most pregnant women who have PKU can have healthy pregnancies and healthy babies.
The medicine Kuvan® (sapropterin dihydrochloride) can help some people with PKU. The medicine is more likely to work in people
with mild or special forms of PKU. Children who take Kuvan® must follow a special meal plan, but it may not be as strict as one for
those not taking the drug. They still need regular blood tests to check phenylalanine levels.