What treatment could be given to babies with PKU to avoid the harmful effects?

Phenylketonuria (fen-ul-kee-tuh-NUR-ee-uh), or PKU, is a metabolic disorder that some babies are born with. It's caused by a defect in the enzyme that breaks down the amino acid phenylalanine.

Newborn babies in the United States have their blood tested for PKU as part of newborn screening. This lets doctors start treatment, usually a special diet, right away to help prevent problems.

What Are the Signs & Symptoms of PKU?

The body uses amino acids to build proteins. Phenylalanine (fen-ul-AL-uh-neen) is needed for normal growth in infants and children and for normal protein production. But if too much builds up in the body, the brain is affected. Phenylketonuria that's not treated can lead to developmental delays and permanent intellectual disability.

Phenylalanine also affects melanin, the pigment responsible for hair color and skin color. So kids with PKU often have fair skin, light hair, and blue eyes.

A child with PKU may also have:

• seizures
• growth problems
• behavioral problems
• skin rashes
• a musty odor to the breath, skin, or urine (pee) from too much phenylalanine in the body

What Causes PKU?

Phenylalanine is one of the eight amino acids that we get only from food sources. Usually, the body breaks down phenylalanine with an enzyme called phenylalanine hydroxylase (PAH) to make proteins.

People with PKU are born with an inherited defect in the gene that controls the production of PAH. So their bodies can't break down phenylalanine properly.

How Is PKU Diagnosed?

All newborn babies in the United States have their blood tested for signs of PKU as part of newborn screening.

How Is Phenylketonuria Treated?

Treatment for PKU involves following a strict diet that is low in phenylalanine. Babies with PKU need to be on a special formula as soon as possible.

Children and adults with PKU should eat a low-protein diet. They should avoid high-protein foods, like milk, dairy, meats, eggs, nuts, soy, and beans. A person with PKU also should avoid the artificial sweetener aspartame, which contains phenylalanine. Special formulas may be needed at any age for the person to get the right amount of calories and essential nutrients.

The special diet should start as soon as PKU is diagnosed and continue for the rest of the person's life. New medicines are being developed to lower PKU in the blood, but medical nutrition therapy is the main treatment for PKU.

What Else Should I Know?

PKU is treatable when found early. Doctors will closely watch kids who have it. People with PKU must strictly follow the right diet for the rest of their lives. This can prevent the problems caused by too much phenylalanine.

If your child has phenylketonuria, work with the health care team to help keep phenylalanine levels in an acceptable range. Your doctor will check the level of phenylalanine in your child's blood regularly.

Because PKU is a genetic condition, you may want to speak to a genetic counselor about testing other family members and how PKU runs in families. You also can find more information and support online at:

Phenylketonuria (PKU) is a rare metabolic disorder. Children with PKU can’t process an amino acid called phenylalanine. Phenylalanine is in many common foods. It helps the body make protein. It's also important for brain growth. It's normally changed to tyrosine, which helps create all of the body's proteins. But with PKU, the amino acid can build up in the bloodstream and cause harm. PKU is found with a simple blood test. All newborn babies in the U.S. are screened for PKU.

What causes PKU in a child?

PKU is caused by a defect in a gene known as the PAH gene. This defect changes the way that phenylalanine is broken down by the body during digestion. PKU is passed on to children when each parent has 1 mutated gene. This means that neither parent has any symptoms of PKU, but both are carriers of the faulty gene. PKU is an autosomal recessive disease. This means that a child needs to inherit 1 faulty gene from each parent to show signs of the disorder.

Which children are at risk for PKU?

A child is at risk for PKU if their parents each have 1 faulty PAH gene. PKU affects 1 out of every 10,000 to 15,000 newborns born in the U.S.

What are the symptoms of PKU in a child?

If a baby is not tested and has undiagnosed PKU, they may show signs or symptoms at several months old. Some babies with PKU may seem more drowsy and listless than normal. They may have feeding problems. As they continue to take in protein and phenylalanine through their diets, they may have growth, mood, behavior, and thinking problems, seizures as well as other problems. Symptoms can range from mild to severe based on how much phenylalanine is in the blood.

The symptoms of PKU can be like other health conditions. Make sure your child sees their healthcare provider for a diagnosis.

How is PKU diagnosed in a child?

All newborn babies in the U.S. are screened for PKU with a blood test. If you adopt a child from another country, they may need to be screened for PKU and other genetic diseases.

How is PKU treated in a child?

PKU is treated with a special diet. Newborn babies who test positive for PKU are placed on phenylalanine-free formula right away.

As babies start to eat solid food, their diet will need to be restricted. This is because phenylalanine is found in many foods with protein. A child with PKU should not eat milk, fish, cheese, nuts, beans, or meat. A child with PKU can eat many foods low in protein, such as vegetables, fruits, and some cereals. Your child may also need to take mineral and vitamin supplements to make up for nutrients missing from the diet.

Children with PKU can’t tolerate the sugar substitute called aspartame. Aspartame contains phenylalanine. You will need to read all food labels to make sure your child avoids foods and drinks that contain this sweetener.

Babies born with a mild degree of PKU have partial enzyme activity. They'll only develop a mild increase in blood phenylalanine levels. These babies may not need any specialized diet or treatment.

What are possible complications of PKU in a child?

A baby born to a woman who has PKU that is not controlled with a special diet is at high risk for serious problems. The developing baby in the uterus can be exposed to very high levels of phenylalanine. This can cause low birth weight, slow growth, small head, behavior problems, and heart disorders. These mothers are also at risk for pregnancy loss.

If PKU in a child is not diagnosed and treated, phenylalanine will build up in the bloodstream until it reaches levels that can cause brain damage. It can also cause permanent damage to organs and tissues around the body. PKU can lead to:

• Developmental delays
• Heart defects, especially in infants born to mothers with PKU and uncontrolled phenylalanine in pregnancy
• Autism
• Intellectual disability
• Very small head size (microcephaly)
• Behavioral problems
• Seizures
• Eczema (a skin condition marked by an itchy red rash or blisters)
• Pale hair and skin compared with other family members
• Delayed physical growth
• Musty body odor

How can I help prevent PKU in my child?

Women with PKU who are of childbearing age should be careful to follow a strict low-protein diet. Your healthcare provider may advise genetic counseling. You can discuss with a counselor the risk for PKU in a future pregnancy.

How can I help my child live with PKU?

Children born with PKU will need to follow a lifelong low-protein diet and stay away from aspartame. If they don't, they may have mood disorders, poor memory and problem-solving skills, depression, and uncontrollable shaking (tremors).

What is the most effective treatment for PKU?

Are there any treatments or cures for PKU?

How can brain damage be prevented in babies diagnosed with PKU?

What is the first line treatment for PKU?