Phenylketonuria (Pku)

1 What is Phenylketonuria (PKU)?

A rare inherited disorder that can cause amino acid phenylalanine that will build up in your body is called Phenylketonuria (fen-ul-ke-toe-NU-re-uh) or PKU.

The cause of this is a defect in the gene that helps in creating the enzyme needed to break down phenylalanine. A dangerous buildup may develop if a person with PKU eats foods that are high in protein will happen if there is no enzyme necessary to process phenylalanine.

With regards to eating, people who have PKU will have to limit their phenylalanine that is most common in foods that has protein.

After birth babies in the United States as well as in other countries are screened for PKU to prevent major health conditions.

2 Symptoms

Newborns do not have any symptoms of phenylketonuria (PKU) at first but it will be developed after a few months without treatment.

Signs and symptoms of PKU may be mild or severe and they include:

  • delayed development;
  • psychiatric disorders;
  • intellectual disability or mental retardation;
  • emotional, social and behavioral problems;
  • hyperactivity;
  • skin rashes or eczema;
  • poor bone strength;
  • neurological problems that may be associated with seizures;
  • abnormally small head (microcephaly);
  • musty odor in breath, urine or skin because of too much phenylalanine;
  • blue eyes and fair skin.

The classic PKU is the severe type of this disorder and can lead to a risk of having brain damage. But even if your PKU is not severe, you may need to follow strict PKU diet to prevent complications and intellectual disability.

If you have a PKU and at the same time became pregnant, you will have maternal PKU. To avoid harming the developing fetus or miscarriage, you must follow the PKU diet so that your blood phenylalanine will not become high.

Babies often will not inherit the PKU but will have complications if their mother’s phenylalanine is high.

These complications are:

  • low birth weight;
  • abnormally small head;
  • intellectual disability;
  • delayed development;
  • behavioral problems;
  • heart defects.

Consult your doctor if

  • for newborns – the baby is positive for PKU screening, he will have dietary treatment to prevent long term problems;
  • for women of childbearing years – consult your doctor if you have a history of PKU before becoming pregnant to reduce high blood phenylalanine;
  • for adults – continuous treatment to slow damage to the central nervous system and to improve mental function. 

3 Causes

The cause of phenylketonuria is a genetic mutation that lacks or deficiency of the enzyme that needed to process amino acid called phenylalanine.

A buildup of this amino acid may develop if a person with PKU eats foods that are high in protein like cheese, milk, meat or nuts.

The father and mother must have a PKU and pass on the defective gene that will be inherited by their child and this is called autosomal recessive in which it is possible for a parent to have the defective gene but not the disease (carrier).

There is no risk if only one parent has the defective gene, but it will be possible for the child to be the carrier.

4 Making a Diagnosis

Newborn screening is the way to diagnose phenylketonuria (PKU).

Your will be referred to a specialized hospital or clinic with a doctor who specializes in treating PKU and a dietician once your child is diagnosed with phenylketonuria.

Ask a family member or a close friend to accompany you to the clinic.

Write down questions that you might want to ask your doctor.

Some of the questions are:

  • What is PKU?
  • How did my child get PKU?
  • Do I have it too?
  • How can we manage this disease?
  • What treatments are you going to recommend?
  • Will my child be on a strict diet?
  • If so, will it be for life?
  • What formula will my child need?
  • Are there supplements needed?
  • What will happen to my child if he accidentally eats a food he is not supposed to eat?
  • Is this temporary or long term?
  • If I’ll have another child, what are the chances he/she will get it?

Your doctor will also ask you questions such as:

  • Are you bothered by your child’s symptoms?
  • Do you have any concern about your child’s diet?
  • Have your child’s growth and development normal?

All 50 states in the United States require PKU screening for newborns as well as other countries because this identifies almost all cases of phenylketonuria.

Your doctor might suggest screening tests before and after pregnancy if you have a family history of PKU and this is usually done a day or two after the baby was born not before the baby is 24 hours or if he ingested some protein to make the results accurate. A nurse will draw blood from your baby’s heel and will be sent to the laboratory for testing.

You will need to schedule a newborn screening if you did not give birth in the hospital.

If the result is positive for PKU:

  • both of you will have to undergo a genetic testing to identify gene mutations;
  • your baby will have to undergo additional tests such as urine test and more blood tests to confirm if he really has PKU.

5 Treatment

Treatments for phenylketonuria (PKU) include:

  • a lifetime diet with limited intake of foods with protein;
  • a PKU formula, a nutritional supplement to ensure that you will have enough protein without the phenylalanine for a lifetime.

Your doctor will determine the amount of phenylalanine that you consumed by:

  • frequent blood tests that will monitor your PKU levels;
  • regular review of growth charts, diet records and blood levels of phenylalanine;
  • and other tests that can see development, health and growth of the person.

Your doctor will most likely refer you to a registered dietician regarding your PKU diet. The foods that you need to avoid because of their high protein content include:

  • cheese,
  • milk,
  • nuts,
  • eggs,
  • beans,
  • soybeans,
  • beef,
  • pork,
  • chicken
  • and fish.

You will need to limit your food intake of

  • grains,
  • potatoes and other vegetables that have protein,
  • and diet sodas or other drinks that contain aspartame (Equal, NutraSweet) because this releases phenylalanine.

Even some supplements and vitamins have aspartame or may have skim milk or amino acids. Consult your doctor first about these medications.

There are formulas available for PKU people to get essential nutrition. Breast milk and formulated milk have phenylalanine so your dietician will make milk that is phenylalanine-free infant formula.

When your child starts to eat solid foods, you can give him foods that have low levels of phenylalanine. These foods replace the phenylalanine a baby has been receiving from breast milk or formula milk.

For adults and older children, they will still need to follow their diet. Your formula will be divided in between your meals and snacks and can be an essential nutritional substance.

Neutral amino acid therapy in tablet or powder is another PKU diet that can block some of the phenylalanine.

Consult your doctor first before taking this. This is a lifestyle change that can be challenging for both the mother and the child.

The drug sapropterin (Kuvan) has been approved for the treatment of PKU by the Food and Drug Administration (FDA).

Your tolerance with phenylalanine will be increased and cab used along with the PKU diet, but this does not work for anyone with PKU.

There is still an ongoing study about the efficacy and safety of sapropterin.

6 Prevention

Since Phenylketonuria (PKU) is inherited genetically, it is not easy to prevent.

If you are a woman with phenylketonuria who wants to be pregnant:

  • follow a low phenylalanine diet to prevent birth defects;
  • consider genetic counseling or preconception genetic counseling if you have a family history of PKU so that you can fully understand how this is passed from generations to generations.

A doctor who specializes in medical genetics can help you with this as well as assist you with family planning.

7 Alternative and Homeopathic Remedies

Consult with your physician before starting any alternative remedies for phenylketonuria (PKU).

People who have PKU are unable to metabolize the amino acid phenylalanine.

Tyrosine is a non-essential amino acid (protein building block) supplement that may be beneficial in some people with PKU, though evidences are still preliminary.

8 Lifestyle and Coping

Lifestyle modifications are necessary in order to cope with phenylketonuria (PKU).

You need to keep records of the food that you are eating every day that is recommended by your dietician.

If you want to be accurate, use standard cups and spoons or a kitchen scale that reads in grams to measure the portions of your food.

The food intakes will be used to calculate the amount of phenylalanine eaten every day.

Computer programs or food diaries are available that list the amounts of phenylalanine in solid foods, baby foods and cooking ingredients.

Buying low-protein products that may add variety to your diet and available at food retailers.

Consult your dietician on how to be creative in foods like creating a whole different menu that has low-protein ingredients at the same time you can add low-phenylalanine seasonings to add flavor, but do not forget to measure every ingredient.

Ask your dietician on how to manage your other condition if you have a one.

9 Risks and Complications

There are several risks and complications associated with phenylketonuria (PKU).

The risk factors for phenylketonuria:

  • having two parents with the defective PKU gene, most likely your child will have the disease;
  • certain ethnic decent, less common in Africa than in any other ethnic group;
  • a child whose mother did not follow the PKU diet during pregnancy will be at risk of birth defects because of the phenylalanine in his mother’s blood.

Phenylketonuria, if left untreated can lead to:

  • abnormally small head (microcephaly);
  • irreversible brain damage;
  • intellectual disability;
  • significant mental and health problems;
  • neurological problems such as tremors and seizures;
  • social, behavioral and emotional problem.