What is Phenylketonuria (PKU)?
Phenylketonuria (PKU) is a genetic disorder in which large amounts of a substance called phenylalanine accumulate in the body. Phenylalanine is found in the body as part of normal biochemical pathways, but problems arise when levels are consistently above normal.
Phenylalanine is an amino acid. Amino acids are the molecules that make up proteins. Most of the foods you eat contain protein and aspartame, an artificial sweetener, contains phenylalanine. If this condition is not treated, the accumulation of phenylalanine in the body causes symptoms, including problems with cognitive development (mental retardation).
What are the types of phenylketonuria?
There are different types of PKU depending on the severity of the diagnosis. Symptoms worsen in severe cases in those who are not treated. Types of PKU include:
- Classic phenylketonuria (most severe).
- Moderate or mild phenylketonuria.
- Mild hyperphenylalaninemia (less severe).
Who gets phenylketonuria?
PKU can occur in anyone with mutations in both copies of the FAH gene.
If a woman with uncontrolled PKU has high levels of phenylalanine during pregnancy, it can lead to mental retardation, birth defects, and other problems in the baby, even if the baby does not have PKU.
What are the symptoms of phenylketonuria?
Because diagnosis and treatment of PKU most often occur shortly after birth due to abnormalities in newborn screening, noticeable symptoms are very rare. Symptoms affect those who are not diagnosed or not treated.
Symptoms of untreated PKU include:
- Eczema.
- Change in skin and/or hair color (lighter than other members of their family).
- Small head size (microcephaly).
- Musty smell from the mouth, skin or urine.
Serious symptoms of untreated PKU include:
- Behavioral problems.
- Delays in development.
- Limited intellectual abilities.
- Seizures (rare).
Children and adults with mild hyperphenylalaninemia have a much lower risk of mental retardation if left untreated.
What causes phenylketonuria?
Mutations in both copies of the FAH gene cause PKU. The PAH gene instructs your body to make an enzyme (phenylalanine hydroxylase) that is responsible for converting amino acids into compounds (proteins) that your body can use. When your body can't process the amino acids you eat, they accumulate in your blood and tissues. Your body is sensitive to phenylalanine. Too much phenylalanine in your body damages your brain.
Is phenylketonuria dominant or recessive?
PKU is a genetic disease transmitted to children from parents in an autosomal recessive manner. This means that children receive one copy of the mutated gene that causes PKU from each parent at the time of conception. In most cases, parents are carriers of the gene but do not show symptoms of the disease.
How is phenylketonuria diagnosed?
Doctors confirm the diagnosis of PKU shortly after birth as part of routine newborn screening with a blood test. If the level of phenylalanine in your child's blood sample is high, the doctor will order additional tests to confirm the diagnosis and type of PKU, usually with additional blood or urine tests. Because PKU is a genetic disorder, a genetic test can identify the mutation responsible for the symptoms.
Although most cases of PKU are diagnosed shortly after the baby is born, doctors can diagnose PKU at any age if newborns have not been screened.
Are there screening tests to diagnose phenylketonuria?
The phenylalanine screening test measures the level of phenylalanine in the blood. Newborns have this test between 24 and 72 hours after birth as part of newborn screening. Your doctor will take a blood sample from your child's heel by piercing it with a small needle. This test only requires a few drops of blood.
How is phenylketonuria treated?
Treatment for PKU is lifelong. This may include a special diet or medication.
Treatment may include:
- Eat a special diet low in phenylalanine but rich in nutrients.
- Take vitamins, minerals and supplements.
What foods contain phenylalanine?
A person diagnosed with PKU must follow a special diet that limits the amount of foods containing phenylalanine. You can find phenylalanine in protein-rich foods, including:
- Milk.
- Eggs.
- Cheese.
- Nuts.
- Fish.
- Chicken.
- Beef.
- Beans.
- Artificial sweetener (aspartame).
Is there a diet for phenylketonuria?
A low-protein diet is best for people with PKU unless they are treated with pegvaliasis. You should avoid high protein foods such as meat, eggs, and dairy products. If you or your child has PKU, talk to your doctor or dietitian about creating a well-balanced diet rich in essential nutrients.
How can I prevent phenylketonuria?
There is no way to prevent PKU. If you are planning to become pregnant and want to understand the risk of having a baby with a genetic disorder, talk to your doctor about genetic testing.
What should I expect if I have phenylketonuria?
PKU is a lifelong disease, and most patients lead a healthy lifestyle. Once diagnosed, regular blood tests are needed to monitor blood levels of phenylalanine.
For those on a restrictive diet, many people benefit from working closely with a nutritionist who can advise you on the best foods to avoid and how to get all the nutrients you need to stay healthy.
If you have PKU and are pregnant, your doctor and/or dietitian will recommend a diet that will provide you with adequate nutrition and reduce the risk of complications for your baby.
How can I take care of myself?
Your diagnosis of PKU is irreversible, so stay tuned with your doctor and get regular blood tests to monitor your body's phenylalanine levels.
If you are on a strict diet, you still need to eat foods and take vitamins to make up for the lack of protein in your diet. Be sure to follow the diet for life to prevent symptoms that could be dangerous to your health.
If you are planning to become pregnant, talk to your doctor about genetic testing to understand the risk of having a child with a genetic disorder.