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Phenylketonuria (PKU)

Phenylketonuria (PKU)

What is Phenylketonuria (PKU)?

Phenylketonuria (PKU) is a rare, genetic disorder caused by a defect in the gene that helps produce the enzyme needed to break down an amino acid called phenylalanine. This leads to a dangerous build-up of phenylalanine in the body whenever the child/adult eats foods with proteins, aspartame or artificial sweeteners. Left untreated, the build-up of phenylalanine can lead to intellectual disability and other health issues like epilepsy, eczema and vomiting.

Children and adults with PKU will have to be on a lifelong diet which restricts the intake of phenylalanine. Special foods are available for PKU patients.

PKU is inherited in an autosomal recessive pattern which means each parent carries a defective copy of the gene. The risk for two carrier parents to have a child with PKU is 25% with each pregnancy. Both males and females are at a risk for PKU.

There are more than 300 variants of the PKU gene. Different mutations result in varying levels of enzyme production to break down phenylalanine. It is important to identify the mutation and the level of phenylalanine in the blood to adjust the individual’s diet and treatment plan.

Newborn babies with PKU do not display any symptoms until a few months later. Within a few months, the following symptoms may occur:

  • A musty odor in the skin, breath or urine caused by too much phenylalanine
  • Seizures
  • Skin rashes like red boils
  • Vomiting
  • Small head (microcephaly)
  • Hyperactivity
  • Intellectual impairment
  • Delayed developmental milestones
  • Behavioural problems
  • Psychiatric symptoms

To avoid severe intellectual impairment, it is important to immediately start the baby on a diet and control the levels of phenylalanine in the blood.

If the pediatrician/physician/neurologists suspects PKU, he/she will usually take a family history and history of the child’s/adult’s symptoms along with a detailed clinical examination. Some of the tests that are used to diagnose PKU include:

  • Levels of phenylalanine in the blood
  • Genetic testing

Currently, newborn screening can check for PKU. Babies around 5 days old are offered newborn heel stick blood testing to check for PKU and other inherited metabolic disorders. Most private hospitals in India offer a newborn screening panel for such disorders.

Currently, no cure is available for PKU except diet and special foods. The objective of PKU treatment is to maintain serum phenylalanine at levels within 2-6 mg/dL. This can be done through a strict diet restricting proteins. Babies which have been put on a diet as young as 3 months do not show any intellectual impairment and have a normal IQ. It is important to stick to a diet with low protein. Ideal foods include fruits, vegetables, juices and special low-protein foods. Currently Pristine Metanutrition foods ( has an amino acid based, phenylalanine-free powdered formula which can be used for infants and children up to 3 years of age.

A low-protein diet can be maintained even in adulthood to avoid complications.

Foods to avoid:

  • Milk
  • Cheese
  • Nuts
  • Eggs
  • Soybeans
  • Beans
  • Chicken
  • Fish
  • Pork
  • Beef
  • Potatoes
  • Any artificial sweeteners

New drugs targeting PKU:

In 2007, the US FDA approved sapropterin hydrochloride (Kuvan) to treat PKU. Kuvan is an oral formulation of BH4. Kuvan has to be used along with a diet low in protein.

In 2008, the US FDA approved an injectable enzyme therapy called pegvaliase-pqpz (Palynziq) for patients with uncontrolled phenylalanine levels.

Both Kuvan and Palynziq are manufactured by BioMarin Pharmaceutical Inc.

Children and adults with PKU can lead fairly normal lives with exercise and other activities provided they stick to the special low-protein diet. Children must be encouraged to comply with restrictions by providing them packaged meals for schools, playtime and outings. They must be strictly told not to accept food from anyone or eat anything outside without checking with their parents/guardians. Restaurant outings must be strictly supervised by adults who should check the ingredients before allowing children to consume food items.

MERD India Foundation – Metabolic Errors and Rare Diseases Organization of India

Contact the foundation for membership and support for PKU

If there is a known case of PKU in the family, it is absolutely essential for closest female relatives like siblings, uncles, aunts and cousins to test for carrier status.

If a woman with a carrier status is pregnant, prenatal test is essential to determine if the fetus has the disease mutation.