PHENYLKETONURIA (PKU)

Phenylketonuria (PKU) is a rare genetic disorder characterized by the body’s inability to metabolize phenylalanine, an essential amino acid found in many protein-containing foods. This condition, if left untreated, can lead to severe intellectual disability and other health complications. While there’s no cure, timely treatment can enable your baby to lead a healthy life.

Causes of Phenylketonuria (PKU)

PKU is caused by a defect in the gene responsible for producing an enzyme called phenylalanine hydroxylase (PAH). This enzyme is essential for breaking down phenylalanine in the body. When PAH is deficient or absent, phenylalanine builds up to toxic levels in the blood, leading to damage in the brain and nervous system.

Prevalence of Phenylketonuria (PKU)

PKU is considered a rare disorder, with an estimated prevalence of approximately 1 in 10,000 to 15,000 newborns worldwide. However, prevalence rates may vary among different populations and ethnic groups.

Symptoms of Phenylketonuria (PKU)

Symptoms of PKU may vary depending on the severity of the condition and the individual’s ability to metabolize phenylalanine. Common symptoms include:

Developmental delays
Intellectual disability
Behavioral problems
Seizures
Hyperactivity
Eczema
Musty odor in the breath, skin, and urine (due to the buildup of phenylalanine)

Risk Factors for Phenylketonuria (PKU)

The primary risk factor for PKU is inheriting a mutated gene from both parents. Individuals with a family history of PKU are at an increased risk of having a child with the condition.

Diagnosis of Phenylketonuria (PKU)

Your newborn may appear healthy with all the expected features, but unseen problems can exist. A routine blood test is conducted to detect rare conditions like phenylketonuria (PKU), which poses risks to your baby’s developing brain.

PKU is a rare genetic disorder affecting metabolism, the body’s process of converting food into energy. Babies with PKU lack an enzyme necessary to break down phenylalanine (Phe), an amino acid present in protein. The accumulation of Phe in the bloodstream can lead to harmful effects.

In the United States, every newborn undergoes screening for PKU along with other conditions shortly after birth.

Timing and Procedure of the Test:

Healthcare providers typically collect a blood sample from your baby no earlier than 24 hours after birth. If you delivered outside a hospital, ensure your baby receives the screening at a doctor’s office within a couple of days.

Usually, a small blood sample is obtained from your baby’s heel using a gentle prick. This blood is then transferred onto special paper and sent to a laboratory for analysis. Your baby’s doctor will communicate the results to you.

Interpreting the Results:

The test assesses the level of Phe in your baby’s blood.

A Phe level below 2 milligrams per deciliter (mg/dL) is considered normal, while over 4 mg/dL is deemed high. However, elevated levels do not definitively indicate PKU; further testing is required for confirmation.
Premature babies may exhibit “false positive” results due to the incomplete development of the enzyme required to metabolize Phe.
Conversely, “false negative” results may occur if the baby hasn’t consumed food, is vomiting, or if the test is conducted too soon after birth.

Importance of the PKU Test

Prompt diagnosis and treatment of phenylketonuria (PKU) are crucial to prevent lasting complications, including:

Developmental delays
Reduced IQ
Mood disorders
Hyperactivity
Severe intellectual disability

Treatment of Phenylketonuria (PKU)

For children diagnosed with PKU, adherence to a specialized, lifelong diet low in phenylalanine (Phe) is essential. Initiation of this diet should ideally occur within the first week or ten days after birth.

Dietary Management: Children with PKU typically rely on Phe-free infant formula, with some potentially able to consume breast milk as well. A registered dietitian specialized in PKU can create an individualized eating plan to support optimal growth and development.
Dietary Restrictions: Specific foods high in Phe, such as dairy, eggs, meat, nuts, beans, and products containing the artificial sweetener aspartame, are typically avoided. Instead, carefully measured portions of fruits, vegetables, and low-protein cereals, bread, and pasta are recommended.
Supplementation: Since the diet is restrictive, children often require a special formula containing protein without Phe and other necessary nutrients.
Monitoring: Regular blood tests and medical check-ups are essential to assess the effectiveness of the dietary regimen.
Medication: Some individuals with PKU, particularly those with milder forms of the condition, may benefit from medications like sapropterin (Kuvan) to aid in Phe metabolism. This medication can provide additional dietary flexibility while maintaining the special meal plan.
Long-term Management: Controlling Phe levels is a lifelong process. Adults with uncontrolled PKU may benefit from medications like pegvaliase-pqpz (Palynziq) to reduce Phe levels.

Home Care Tips for Phenylketonuria (PKU)

Follow a strict low-phenylalanine diet as prescribed by your healthcare provider.
Monitor phenylalanine levels regularly through blood tests.
Take prescribed medications as directed.
Attend regular follow-up appointments with your healthcare team.

Prevention of Phenylketonuria (PKU)

Since PKU is a genetic disorder, it cannot be prevented. However, genetic counseling may be beneficial for individuals with a family history of PKU who are planning to have children. Prenatal testing can also help identify fetuses at risk of inheriting the condition.

When to See a Doctor

If you suspect that you or your child may have PKU or if you have a family history of the condition, it is essential to consult a healthcare professional promptly. Early diagnosis and intervention can help prevent or minimize the long-term complications associated with PKU.

Outlook/Prognosis for Phenylketonuria (PKU)

With early diagnosis and adherence to a low-phenylalanine diet, individuals with PKU can lead relatively normal lives. However, untreated or poorly managed PKU can result in severe intellectual disability, developmental delays, and other health problems. Regular monitoring and ongoing management are essential for maintaining optimal health and well-being.

Sources

National Institutes of Health. (2022). Phenylketonuria. Genetics Home Reference.
National PKU Alliance. (n.d.). About PKU.
CDC: “Newborn Screening.”
The Nemours Foundation: “Newborn Screening Tests.”
March of Dimes: “PKU (Phenylketonuria) In Your Baby.”
Academy of Nutrition and Dietetics: “How to Create a PKU-Friendly Diet.”
Eunice Kennedy Shriver National Institute of Child Health and Human Development: “What are common treatments for phenylketonuria (PKU)?”
American College of Medical Genetics and Genomics. (2014). Phenylalanine hydroxylase deficiency: diagnosis and management guideline. Genetics in Medicine, 16(2), 188–200.

Phenylketonuria PKU