Phenylalanine Hydroxylase Deficiency (PKU) | Condition

Phenylalanine Hydroxylase Deficiency (PKU)

UNITY Fetal Risk™ Screen provides an accurate fetal risk estimate for phenylalanine hydroxylase deficiency without requiring a partner sample, as early as 9 weeks of pregnancy. Phenylalanine hydroxylase deficiency, including PKU, is a metabolic disorder that prevents the body from breaking down phenylalanine, an amino acid that can build up to harmful levels and cause intellectual disability if untreated. A strict low-phenylalanine diet and enzyme replacement therapy can help manage symptoms and prevent complications.

Carrier Rate/ Incidence

1 in 79 people are carriers of phenylalanine hydroxylase deficiency (PKU).

Common symptoms

If untreated, PKU can cause severe to profound intellectual disability, learning disabilities, psychiatric conditions and other neurological problems, such as tremors and epilepsy.

Emerging Treatments

Along with diet changes, there are FDA-approved enzyme replacement therapies that are successful in treating those with PKU. Additional treatments, including gene therapies, are under investigation.

What is UNITY Fetal Risk™ Screen for phenylalanine hydroxylase deficiency (PKU)?

UNITY Fetal Risk Screen is a carrier screening and fetal risk assessment for your pregnancy all in one convenient test. The first step is identifying if you are a carrier for PKU. If you are not a carrier for PKU, your baby’s risk of having PKU is extremely low. If you are a carrier and currently pregnant, UNITY Fetal Risk Screen will automatically perform a fetal risk assessment using cfDNA to tell you if your baby’s risk of having PKU is high or low.

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Phenylalanine hydroxylase deficiency (PKU) carrier screening is recommended for anyone planning to start a family or those who are already pregnant that have a family history of PKU or intellectual disability suggestive of PKU.

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What is phenylalanine hydroxylase deficiency?

Phenylalanine Hydroxylase Deficiency, also known as phenylketonuria (PKU), is an inherited condition where the body can't break down a substance called phenylalanine. Since phenylalanine is found in many foods with protein and in some artificial sweeteners, people with PKU have to eat a special diet. If they don't, it can cause problems like learning difficulties, behavior issues, and seizures because too much phenylalanine can damage the brain as it grows. With early and continuous treatment, which mainly includes eating a low-phenylalanine diet and using special formulas to help with growth and nutrition, people with PKU can live normally. It's important for those with PKU to work closely with doctors and nutritionists to manage it well throughout their life.

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How is phenylalanine hydroxylase deficiency inherited?

PKU is an autosomal recessive condition, meaning a person must inherit a specific genetic change in the PAH gene from both parents to be affected. If both parents are carriers, they can pass on either a working or non-working copy of the PAH gene. If a child inherits non-working copies from both parents, they will have PKU.

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Who should consider phenylalanine hydroxylase deficiency screening?

Carrier screening for phenylalanine hydroxylase deficiency is recommended for pregnant individuals or those considering pregnancy who have a family history of PKU or intellectual disabilities suggestive of PKU.

With UNITY Fetal Risk Screen one test can tell you if you are a carrier for PKU and if your baby has a high risk or low risk of having PKU through our unique fetal risk assessment. Depending on your results, your provider may discuss additional confirmatory testing that can be done either before or after delivery.

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UNITY Fetal Risk Screen Carrier Screening & Fetal Risk Assessment (cfDNA for recessive conditions) workflow

Test as early as 9 weeks

Your blood sample can be collected in the doctor’s office, at a local lab, or through our mobile services. Your blood sample is shipped to our CAP/CLIA certified laboratory in northern California.

UNITY Aneuploidy™ Screen + UNITY Fetal RhD™ and Fetal Antigen™ results as early as 10 weeks
Within about one week from lab receipt, your doctor will receive the baby’s risk score for aneuploidies (chromosome conditions) and fetal RhD and fetal antigens (if added). You will receive a text or email indicating your results are available on our portal, or your healthcare provider may call you with the results.

Carrier status + fetal risk assessment results as early as week 11
Within about two weeks from lab receipt, your doctor will receive the results of your maternal carrier status testing and fetal risk assessment. If you were found to be a carrier for any of the recessive conditions, fetal risk assessment is automatically run to determine your baby’s risk of being affected. You will receive a text or email indicating your results are available on our portal, or your healthcare provider may call you with the results.

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What do phenylalanine hydroxylase deficiency screening results mean?

Your UNITY Fetal Risk Screen results will tell you if you are a carrier for PKU, or other recessive conditions. Then, if you are currently pregnant and a carrier for one or more of the conditions screened, a fetal risk assessment using cfDNA will automatically be performed on your sample. Your UNITY Fetal Risk Screen will show your baby’s risk of being affected by PKU.

If your results show a high-risk, your healthcare provider will discuss the recommended confirmatory testing that can be performed before or after delivery.

UNITY Fetal Risk Screen results are not diagnostic, so there is always the option for additional confirmatory testing to be performed. You can discuss your options and recommendations with your provider or one of our genetic counselors:

Before Birth:
Testing during pregnancy can be performed by obtaining a sample of placenta (chorionic villus sampling or CVS) or fluid around your baby (amniocentesis) which both contain DNA that is representative of your baby. A CVS is ideally performed between 10 to 13 weeks in pregnancy while an amniocentesis is typically performed between 15 to 24 weeks in pregnancy. Both procedures are generally safe, but have a small risk for pregnancy complications, including miscarriage.

After Birth:
Testing for your baby can be performed after birth through a blood test. In addition, all babies born in a hospital in the United States are automatically screened for PKU. The majority of babies with PKU will be diagnosed through this screening process. However, in rare cases, a diagnosis may be missed or incorrectly diagnosed.

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Frequently Asked Questions

Is there a cure for PKU?

Currently, there is no cure for PKU, however, significant advancements have been made in treatments. Most individuals who receive early, proper treatment for PKU have good outcomes and typical life expectancy. Ongoing research includes gene therapy, new medications, and clinical trials.

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How is PKU treated?

Currently, the primary treatment for PKU involves following a lifelong, low phenylalanine (low protein) diet to maintain low levels of phenylalanine in the blood. Diet changes should begin as soon as possible after birth to achieve the best outcomes. Medications and enzyme replacement therapy are also used in children and adults with PKU, with improved outcomes. With adherence to treatment plans, the outlook for those with PKU is favorable.

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How can PKU affect pregnancy and childbirth?

‍PKU can complicate pregnancy, especially if the pregnant person has elevated levels of blood phenylalanine. Pregnant people with PKU that have elevated blood phenylalanine concentrations are at increased risk to have pregnancies with intrauterine growth restriction, congenital heart defects or other birth defects, microcephaly, and intellectual disabilities. Close monitoring by healthcare providers, specialized prenatal care, and managing the condition during pregnancy are crucial to ensure the health of both mother and the baby.

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