Phenylketonuria: Causes, Treatments, and Long-Term Outlook

Phenylketonuria (PKU) is a rare genetic disorder that causes an amino acid to build up to dangerous levels. There is no cure, but with early diagnosis and treatment, you can prevent the negative risks associated with this condition. Learn more here.

7 minute read

Last Updated July 15, 2020

Phenylketonuria: Causes, Treatments, and Long-Term Outlook

Phenylketonuria (PKU) is a rare genetic disorder that causes an amino acid known as phenylalanine to build up. Phenylalanine hydroxylase is an enzyme that converts this amino acid into tyrosine, which you need for the creation of neurotransmitters. 

With PKU, there is a defect in the PAH gene that creates this enzyme, and without it, your body cannot break down phenylalanine, so it builds up to dangerous levels. 

What Causes Phenylketonuria?

Phenylketonuria is an inherited disorder that is caused by a defective PAH gene. This gene creates the enzyme that is required for the breakdown of the amino acid phenylalanine. Without this enzyme, the amino acid can accumulate to dangerous levels as a result of eating high-protein foods.

For a child to develop the condition and symptoms, they must inherit the gene from both parents. If only one parent passes along the gene, the child will be a carrier but will not show symptoms of the condition.

There is no cure, so special diets are required along with other treatment options.

Phenylketonuria Symptoms

The symptoms of PKU can range from mild to severe, with the most severe form of the disease being known as classic PKU. 

PKU is diagnosed during infancy, and many babies may appear normal for months at first. If they are not treated, the following symptoms will start to show:

♦ Seizures
♦ Tremors
♦ Hyperactivity
♦ Stunted growth
♦ Skin conditions like eczema

Women with PKU could be at risk for complications, including miscarriage. It is essential to follow a PKU diet during pregnancy to prevent the chances of the unborn baby being exposed to excessive levels of phenylalanine. Should this happen, the child could be at risk for health problems, including:

♦ Delayed growth
♦ Low birth weight
♦ Abnormally small head size
♦ Intellectual disabilities
♦ Heart defects

Without treatment, the disorder can cause behavioral problems as the child gets older and permanent and irreversible brain damage and intellectual disabilities. Early detection and diagnosis are necessary for treatment to be effective. 

Phenylketonuria Diagnosis

Since the 1960s, hospitals run routine screenings for phenylketonuria on all newborns by taking blood samples. For babies not delivered in hospitals, screenings need to be scheduled within the first few days after birth. 

The key to preventing worsening symptoms and illness is to diagnose phenylketonuria early and begin treatment right away. If tests are not done early, but developmental delays start to show later in childhood, doctors will run enzyme tests to evaluate if the condition has developed.

Phenylketonuria Treatment

There are medications you can take to help treat phenylketonuria. The FDA has approved the use of sapropterin so long as it is used in conjunction with a special PKU diet. This medication acts in the same way as BH4, which is a natural substance in your body that helps the PAH enzyme to break down phenylalanine. 

This medication does not work for everyone; however, so a PKU diet is typically the best way to treat PKY and prevent symptoms.

Phenylketonuria Diet

Following a PKU diet is essential as soon as the condition is diagnosed. This is the only way to prevent symptoms from developing and preventing behavioral and developmental delays. If a child is not diagnosed early on, and symptoms appear later, switching to this diet is the only way to prevent further complications and symptoms. Once diagnosed with PKU, you must follow a special diet for the rest of your life.

The diet must limit foods that contain phenylalanine. Babies can drink breast milk or special formulas that do not contain this amino acid. Once solid foods can be consumed, the following foods need to be avoided:

♦ Cheese
♦ Eggs
♦ Milk
♦ Bans
♦ Chicken
♦ Beef
♦ Pork
♦ Nuts
♦ Fish

Since cutting these foods from the diet will result in a lack of nutritional protein, it is important to give babies a PKU formula that contains all of the amino acids their body will need. 

There are also low-protein, PKU-friendly foods available in specialty health stores. The PKU meal plans will vary for each person, so you need to work with your doctor and nutritionist closely to manage phenylalanine intake and symptoms. 

In some states, there is legislation in place that enables insurance companies to cover foods and formulas required for PKU patients. You should check with your insurance company, as well as the state health department, to find out if your needs can be covered. Even without insurance coverage, there are many state health programs that work to help provide dietary assistance for individuals with PKU.

Natural Treatments for Phenylketonuria

Along with medications and dietary changes, there are also natural supplements you can take to help treat PKU and its symptoms. 

Fish oil: By cutting most high-protein foods, you miss out on essential omega-3 fatty acids, which help to prevent oxidative damage and disease, and they also promote brain health. A daily supplement can help ensure you get the nutrients you are missing from the PKU diet.

♦ Tyrosine: Phenylalanine is supposed to be broken down into this amino acid, but with PKU this cannot happen. Tyrosine is important in the function of neurotransmitters and memory, so a supplement will make sure you get what you need.

Phenylketonuria Statistics

♦ Phenylketonuria occurs in 1 out of every 10,000 to 15,000 newborns.

♦ There is a 1 in 4 chance of an infant developing PKU if both parents are genetic carriers of the mutated gene.

♦ PKU does not shorten a person’s life expectancy.

♦ PKU is more common among individuals of Irish, North American, and Northern European descent.

Phenylketonuria and Children

Phenylketonuria is primarily diagnosed in infancy and impacts children throughout their lives. The condition can be diagnosed within the first few days of birth so that treatment can begin right away. Without prompt treatment, the child will be at risk for developmental delays that can last through adulthood. 

With hospitals running routine screenings these days, severe cases of phenylketonuria are not as common as they used to be.

What Is the Long-Term Outlook?

So long as you follow a PKU diet plan immediately after diagnosis and as close to birth as possible, the long-term outlook is good. If diagnosis and treatment are delayed, the risk of brain damage increases, and intellect and behavior can be negatively impacted within the first year of life. 

Because PKU is genetic, it is possible to determine if you carry the gene, which allows you to start a PKU diet plan earlier. This will help to prevent risks in children and will help protect your own health as well.

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