Metabolic Health
Medically Reviewed iconMedically Reviewedcevron icon

What Is Phenylketonuria?

Phenylketonuria, also known as PKU, is a rare disorder that can cause the buildup of phenylalanine (an amino acid) in the body. This condition happens due to a defect in the genes whose work is to create the enzymes that are needed to break down phenylalanine. 

Depending on the severity of the condition, there are two types of PKU. These include: 

  • Classic PKU: This is the most common type of PKU. This results in severe brain damage and high levels of phenylalanine as the essential enzymes are either missing or severely reduced. 
  • Less severe forms of PKU: As the name suggests, in this type of PKU, the effects are mild and the enzymes do retain some function and the phenylalanine level is not so high.

Phenylketonuria Symptoms

PKU symptoms can range from being mild to severe. In some cases, infants with PKU do not show any signs, and symptoms during the initial phases. If proper treatment is not given to the baby, the following symptoms may appear:

  • Seizures like neurological issues
  • A musty odor from breath, skin, or urine
  • Trembling and shaking
  • Skin issues such as eczema
  • Social and behavioral issues
  • Stunted growth
  • Delay in development
  • Irreversible brain damage
  • Intellectual disabilities

Immediate treatment is crucial in the cases of PKU as it may lead to several lifelong complications in the child. 

Who Is At Risk?

While PKU can occur to anyone, there are a few risk factors that are associated with its development. These risk factors include the following: 

  • Genetics: A child whose parents have a defective gene has fairly high chances of getting PKU. 
  • Ethnic Descent: PKU is less common in African Americans and the defect may vary by ethnic groups.

Phenylketonuria Causes

Since it is a genetic disorder, one of the main phenylketonuria causes is the defect in the genes. The person inherits the defect in the PAH gene that helps in creating phenylalanine hydroxylase, the enzyme responsible for breaking down phenylalanine. 

When a person eats high-protein foods like meat or eggs, it can lead to a dangerous build-up of phenylalanine. This further can affect the nerve cells in the brain. 

Notably, this condition is passed on to the child only when both the parents have the defective gene. In case when only one parent has the defective gene, the child then just becomes a carrier and does not have the disease. Read more to know about what level of blood sugar is dangerous?

Book a Free Session

How does PKU affect the body?

Phenylketonuria is a rare genetic condition that causes a severe build-up of phenylalanine in the body. It is an amino acid that can easily be found in various artificial sweeteners and proteins. To convert this amino acid to tyrosine, the body requires an enzyme called Phenylalanine hydroxylase. This enzyme helps to create multiple neurotransmitters like dopamine, norepinephrine, etc. Phenylketonuria is caused by a defect in the gene that generally helps in creating Phenylalanine hydroxylase. 

If this enzyme goes missing from your body, the body won’t be able to break down phenylalanine, which causes a significant build-up in the body. This build-up can give rise to various health problems that can alter healthy living experiences.

How Is Phenylketonuria Diagnosed?

Phenylketonuria diagnosis is usually done at birth or when the baby is just a day or two old. The basic phenylketonuria test is done by taking the blood samples. Some other tests such as urine tests or genetic tests may be performed to confirm the presence of defects. 

In case a child or adult shows symptoms of PKU, the doctors conduct a blood test to analyze the presence of the enzyme needed to break down phenylalanine. Also know about sugar in urine test.

How Is Phenylketonuria Treated?

PKU treatment focuses on the alleviation of the symptoms and managing a good lifestyle with Healthy Indian Food. So, if you or any of your loved one is looking for a treatment, here is what you can expect: 

  • Medication: The doctors may prescribe specific medicines to help lower phenylalanine levels. 
  • Diet: This is the most effective and used method to treat PKU. The doctors will carefully plan a diet plan that avoids food with high phenylalanine levels. Some supplements may also be recommended. 

How Can Phenylketonuria Be Prevented?

Phenylketonuria prevention cannot be done since it is a genetic disorder. However, if you and your partner have PKU and planning to get pregnant, there are some things you can try to lower the risk of PKU in your baby: 

  • Follow a low-phenylalanine diet after getting a consultation from your doctor. 
  • You can also benefit from genetic counselling. They can help you understand the condition better and assist in family planning. 

Pregnancy and Phenylketonuria

Now that you’re aware of what Phenylketonuria is, it’s essential to learn about its connection with pregnancy. If a woman with Phenylketonuria (PKU) gets pregnant, she remains at a higher risk of complications if she fails to follow a PKU meal during her childbearing years. The complications can be as serious as a miscarriage. 

There also remains a high chance that the unborn baby may get exposed to high phenylalanine levels. If it happens, the baby can be subjected to various problems, including intellectual disabilities, an abnormally small head, heart defects, low birth weight, delayed growth, etc. Although you won’t notice these signs right after birth, the doctor can conduct relevant tests to detect phenylketonuria symptoms.


What is Phenylketonuria Hydroxylase Deficiency?

In simple terms, this deficiency gives rise to an autosomal recessive disorder, making it difficult for the body to process phenylalanine, an essential amino acid. This autosomal recessive disorder is known by the name Phenylketonuria.

Which Enzyme is Deficient in Phenylketonuria?

Phenylalanine hydroxylase is the enzyme that is often found in lower numbers in people diagnosed with Phenylketonuria. Most PKU forms are results of PAH gene mutations on chromosome 12q23. Phenylketonuria enzyme deficiency renders the body unable to process phenylalanine.




This website's content is provided only for educational reasons and is not meant to be a replacement for professional medical advice. Due to individual differences, the reader should contact their physician to decide whether the material is applicable to their case.