Phenylketonuria (PKU) is an inherited metabolic disorder that affects infants and young children.

It is caused by a deficiency in the enzyme phenylalanine hydroxylase (PAH), which is responsible for breaking down the amino acid phenylalanine (Phe) in the body. Without this enzyme, Phe builds up in the blood and can cause serious health problems.

What are the Symptoms of PKU?

The symptoms of PKU can vary in severity, but typically include intellectual disability, seizures, developmental delays, behavioral problems, and skin rashes.

Infants with PKU may also have a musty or mousy odor to their skin, hair, and urine due to the buildup of Phe in the body.

How is PKU Detected?

Pregnant women are routinely screened for PKU during prenatal care, as the disorder can cause birth defects and other health problems in unborn babies.

After birth, all infants in the United States are screened for PKU as part of their newborn screening panel, which typically includes several other genetic and metabolic disorders.

The screening test involves taking a small sample of blood from the baby’s heel and sending it to a laboratory for analysis. If the test comes back positive for PKU, further testing is usually done to confirm the diagnosis.

How is PKU Diagnosed?

If a baby’s screening test comes back positive for PKU, they will need to undergo additional testing to confirm the diagnosis.

This may involve measuring the levels of Phe and other amino acids in the baby’s blood, as well as genetic testing to look for mutations in the PAH gene.

If PKU is diagnosed, treatment usually involves following a strict low-Phe diet for life. This means avoiding high-protein foods like meat, dairy, and eggs, as well as most grains and some vegetables and fruits.

Infants with PKU may need to be fed a special formula that is low in Phe, and may also require supplements of certain nutrients.

What Causes PKU?

PKU is caused by mutations in the PAH gene, which provides instructions for making the enzyme that breaks down Phe. When this enzyme is deficient or absent, Phe builds up in the blood and can cause damage to the brain and nervous system.

PKU is an autosomal recessive disorder, which means that a child must inherit two copies of the defective PAH gene (one from each parent) to develop the disorder. If only one parent carries the gene, the child will not have PKU but may be a carrier.

How is PKU Treated?

The main treatment for PKU is a strict low-Phe diet, which must be followed for life. This means avoiding most high-protein foods and consuming special Phe-free formulas and low-protein foods instead.

Infants with PKU may require specially formulated infant formula that is low in Phe.

In addition to diet, people with PKU may also require supplements of certain vitamins and minerals, such as calcium and iron, as well as regular monitoring of their blood Phe levels.

If blood Phe levels are too high, adjustments may need to be made to the diet or medication.

What is the Prognosis for PKU?

With early and consistent treatment, the prognosis for PKU is generally good.

Children with PKU who receive early and appropriate treatment can often achieve normal cognitive and developmental milestones, although there may still be some mild cognitive impairments or behavioral problems. However, if PKU is left untreated or poorly managed, it can lead to severe intellectual disability, seizures, and other serious health problems.

Conclusion

Phenylketonuria is a serious metabolic disorder that can cause significant health problems if not detected and treated early.

With routine screening and prompt diagnosis, infants with PKU can receive the care and treatment they need to live healthy, productive lives. If you have questions or concerns about PKU or other genetic disorders, talk to your healthcare provider for more information.