What is Phenylketonuria?

Phenylketonuria, which is also referred to as PKU, is a rare condition that affects infants. These babies are born unable to break down phenylalanine, which is an essential amino acid.

This disorder is inherited, and it causes a baby to be born without an enzyme referred to as phenylalanine hydroxylase. This enzyme is required to break down phenylalanine, which is found in food that has protein.

Because this enzyme is missing, the level of phenylalanine will increase within the body, and that could result in damage to the central nervous system, as well as brain damage.

What are the Symptoms of Phenylketonuria?

Symptoms of PKU could be mild, moderate, or severe.

Because phenylalanine affects the production of melanin, infants who have PKU will typically exhibit lighter hair, eyes, and skin.

The most severe form of phenylketonuria is referred to as classic PKU. In this case, the infant would appear normal over the course of the first few months of life, but symptoms will begin to develop. These include shaking, trembling, tremors, seizures, stunted growth, skin conditions, hyperactivity, and a musty odor of the urine, skin, earwax, or breath.

Phenylketonuria Causes

Phenylketonuria (PKU) happens when the gene that makes the enzyme phenylalanine hydroxylase (PAH) mutates. This enzyme converts the amino acid phenylalanine into components your body needs. When the PAH gene is defective, the body can’t break down phenylalanine. Amino acids build protein, but phenylalanine is harmful if allowed to build up. In particular, nerve cells in the brain are sensitive to phenylalanine.

PKU is an inherited trait that parents pass down as a recessive gene. In order for a child to get PKU, both parents have to have a mutated PAH gene. When each parent passes on PKU, the child will have it too. However, sometimes, a parent doesn’t have phenylketonuria but is a carrier, meaning they carry the mutated PAH gene without developing symptoms. If just one of the parents has the mutation, the child doesn’t develop PKU.

When both parents carry the mutation, their child isn’t guaranteed to develop the condition. In some cases, because each parent carries a different versions of the PAH mutation, it’s possible that only one of them will be passed on during conception.

How is Phenylketonuria Treated?

Phenylketonuria needs to be caught and treated early to prevent severe damage and complications. This condition is treatable, however, by following a strict diet that’s extremely low in phenylalanine.

Foods that are high in protein should be avoided. These include fish, pork, beef, chicken, beans, nuts, milk, cheese, and eggs.

Patients can also take sapropterin, which is a medication approved by the FDA to treat PKU. This medicine will be effective in children that have mild cases of the disorder, and it will help to lower phenylalanine levels in the body, but it has to be used with a custom meal plan.

Phenylketonuria Prevention

For women with phenylketonuria, if you’re considering pregnancy, you should take precautions prior to trying to conceive. To help prevent PKU, follow a low-phenylalanine diet prior to becoming pregnant. (Since this gene is passed on during conception, you can’t prevent this birth defect by changing your habits during pregnancy.) As a precaution, talk to your doctor before trying to conceive and follow their recommendations.

Genetic counseling may provide a way to prevent passing PKU on to your child. Choose a specialist in medical genetics to help you understand how PKU is passed down through your family. They can help you determine the risks so that you can make an informed decision prior to planning a family.