Phenylketonuria

This is a rare inherited condition that produces an amino acid (phenylalanine) build-up in the body. This disease is called phenylketonuria or PKU. The cause of this disorder is a mutation (change) in the phenylalanine hydroxylase (PAH) gene. However, this gene is responsible for making enzymes that break down the phenylalanine.

When the body does not have enough enzymes that are used to break down the phenylalanine, it may lead to dangerous build-up. These buildups in the body usually happen when a person with PKU consumes foods that contain protein or aspartame (an artificial sweetener). Not treating this condition may lead to serious health issues.

Furthermore, those who suffer from this condition (including babies, children, and adults) need to follow a diet that limits phenylalanine. This amino acid is usually found in foods that contain protein. However, there are some new medicines that can allow people with PKU to eat foods high in phenylalanine.

Commonly, in the U.S. babies are tested for this condition soon after birth. Despite there is no way to cure this condition, early diagnosis and treatment can help to prevent future complications (including intellectual disability) and other health problems.

Symptoms

Usually, babies do not have any symptoms but without treatment, PKU symptoms can appear within several months after birth. The symptoms caused by this health condition fluctuate from mild to severe. For example:

• Skin rashes (including eczema)
• Neurological problems (such as seizures)
• A musty odor in the skin, urine, or breath due to an increased amount of phenylalanine in the body
• Microcephaly (abnormal small size of the head)
• Intellectual disability
• Hyperactivity
• Social, behavioral, and emotional issues
• Mental disease
• Delayed development
• Such people can also have hair, skin, and eye color lighter than family members. It occurs because the phenylalanine cannot transform into melanin (this is a specific pigment responsible for skin and hair tone).

PKU Types

The severity of the symptoms depends on the PKU type you experience. For example:

• Classic PKU – This is the most severe PKU type because the enzyme that breaks down the phenylalanine is significantly reduced or missing. Thus, the body accumulates increased amounts of this amino acid which can provoke serious brain damage.
• Mild and Moderate PKU – In such cases, the levels of the enzymes are not so low and have some functions. Hence, the phenylalanine is not so high which results in a reduced risk of brain damage.

In any case, a special diet that helps to prevent intellectual disability and other PKU complications is required for babies.

Pregnancy and PKU

If a woman becomes pregnant and suffers from PKU, the risk of maternal PKU increases significantly. In such cases, a special PKU diet is recommended before and during pregnancy. Otherwise, phenylalanine levels can elevate drastically, which can harm the developing baby. However, even mild and moderate PKU forms can increase the baby’s risk of health problems if the PKU diet is not followed by the biological mother. Check below some complications that could happen if the mother’s phenylalanine levels are high:

• Low birth weight
• Abnormal small head
• Heart problems

Furthermore, maternal PKU can cause delayed development, intellectual issues, and behavioral problems.

Causes

The primary PKU cause is a gene mutation. This gene change can cause mild, moderate, or severe PKU. This genetic mutation provokes a decrease or lack of a specific enzyme involved in the phenylalanine breakdown. Life-threatening phenylalanine build-up can occur in people with PKU who eat foods rich in protein including cheese, milk, nuts, or meat, and grains such as bread, pasta, or aspartame.

A child can inherit this health condition if both biological mother and father have and pass on the mutated gene. Such patterns of inheritance are known as autosomal recessive. However, if one parent has this gene and it passes to the child this condition does not happen usually but the child may carry this gene. Most inherited PKU cases occur when both biological parents have this mutated gene but do not know about it.

Risk Factors

• One risk factor that provokes PKU is when both biological parents have this mutated gene and it passes to their children.
• Commonly, PKU impacts people from most ethnic backgrounds in the whole world. For instance, in the U.S. European ancestry is more affected by PKU compared to African ancestry.

Complications

All people who do not receive PKU treatment can experience complications. Furthermore, pregnant women with high phenylalanine levels in the body can lead to serious problems for their unborn babies. Check below some complications that happen if this condition is not treated:

• Permanent brain damage and intellectual disability that occurs in the first several months after birth
• Neurological issues (such as tremors, seizures, and others)
• Serious developmental and health problems
• Emotional, social, and behavioral issues

Is it Possible to Prevent PKU?

Check below some tips for pregnant women with PKU:

• Special PKU Diet – Healthcare providers usually recommend a diet low in phenylalanine for pregnant women. Ideally, this diet should be considered before and during pregnancy. Along with the PKU diet, doctors may recommend special supplements designed for pregnant women to maintain healthy protein levels.
• Genetic Counseling – It is advised to see a specialist in medical genetics before becoming pregnant. This doctor can help to determine the PKU risk of future children and support pregnancy.

Diagnosis

Commonly, all cases of phenylketonuria are identified in newborns. Furthermore, all states in the U.S. require babies to be screened for PKU. However, if you have PKU or a family history of this condition, doctors may recommend screenings before pregnancy or birth. Additionally, a blood test can identify a PKU carrier.

Commonly, to get accurate results, it is advised to perform the test after the baby is 24 hours old and after he/she has some protein in the diet. Thereafter, the doctors will collect a blood sample from the baby’s heel. Blood test helps to determine if your child does not have metabolic disorders (including PKU). However, if the tests indicate your child possibly has PKU, doctors can perform additional blood and urine tests to confirm the condition.

Treatment

Early diagnosis and treatment can help to prevent serious health problems (such as intellectual disability). The primary PKU treatments include a life-long diet that is very limited in foods that contain phenylalanine, special nutritional supplements (that ensure enough nutrients and protein vital for growth and overall health), and medicines.

Generally, it is allowed to consume products that contain phenylalanine but in amounts needed for healthy growth and body processes. Thus, your doctor can determine the safe amount of this amino acid you can add to your diet.

What Foods Should Be Avoided by People with PKU?

The diet for people with PKU involves foods low in protein. Check below some foods to avoid:

• Eggs
• Milk
• Soy products (including tofu, tempeh, soybeans, and milk)
• Nuts
• Cheese
• Beans and peas
• Poultry, pork, beef, and any other meat type
• Fish

However, potatoes, grains, and other vegetables are limited too. Furthermore, certain foods and beverages including diet sodas and other drinks that contain aspartame also should be avoided. Aspartame is an artificial sweetener made with phenylalanine.

Frequently Asked Questions

What happens if someone ignores this condition and does not receive treatment?

Those who do not get treatment for this condition may experience permanent damage to the brain and nervous system, which usually provokes learning disabilities, and behavioral, emotional, and social problems.

What is the primary cause of phenylketonuria (PKU)?

This condition occurs due to a decreased or lack of specific enzymes that break down the phenylalanine. It happens due to a gene mutation. Talk with your healthcare professional for more details.

What are the most common phenylketonuria symptoms?

These include a musty odor in the skin, breath, or urine, seizures, and skin rashes (such as eczema). Immediately contact a healthcare professional if you or your loved one experiences any of the previous symptoms. Ask your doctor if you have additional questions.