5 Things You Should Know About Phenylketonuria

Phenylketonuria (PKU) is a rare genetic disorder in which the enzyme phenylalanine hydroxylase, which is needed to break down the amino acid phenylalanine, is not produced by the body. The National PKU Alliance estimates there are about 16,500 people living with PKU in the United States.

Phenylalanine is found in protein contained in food and in the sweetener aspartame. Without the phenylalanine hydroxylase enzyme, phenylalanine can build up to dangerous levels in the body, leading to irreversible brain damage, neurological problems like seizures and tremors, behavioral problems and other health issues. In the United States babies are screened for PKU at birth.

PKU can range from mild to severe with the most severe form called classic phenylketonuria. Left untreated, children with classic PKU can have delayed development, behavioral issues, seizures and possibly psychiatric diagnoses. A musty odor may be present due to high levels of phenylalanine. Children with PKU generally have light colored hair, skin and eyes as high phenylalanine levels disrupt the production of melanin, needed to provide pigment.

Women who are pregnant with untreated PKU are at risk for problems with fetal growth. The baby may have microcephaly, heart disease, facial or developmental abnormalities.

1. PKU is caused by a genetic mutation.

A defect in the PAH gene causes PKU. This gene creates the instructions that allow the body to produce the enzyme phenylalanine hydroxylase, which is necessary to break down the amino acid phenylalanine. Lacking this enzyme, the body will build up dangerous amounts of phenylalanine leading to severe health issues. The brain is especially responsive to phenylalanine levels, so high amounts can lead to brain damage, depression and other psychiatric disorders.

A baby needs to receive an abnormal PAH gene from both parents for PKU to develop. If they only receive one mutated gene they will be a carrier for PKU but will not develop symptoms.

2. Symptoms often develop several months after birth.

Babies in the U.S. are screened for PKU at birth because they may not show any symptoms of the disorder until several months later. Symptoms may rage from mild to severe and include:

A musty odor on the skin or breath or in urine
Rashes
Seizures or other neurological issues like jerking movements
Fair skin, hair and eyes
Microcephaly (abnormally small head)
Delayed development
Behavioral issues
Psychiatric issues
Intellectual delays

3. PKU is easily diagnosed.

A PKU diagnosis is achieved through a simple blood test. If the test is positive, follow-up urine and blood screening may be ordered to confirm the diagnosis. Additional genetic testing may also be ordered to confirm the mutation of the PAH gene.

4. Treatment for PKU is all about diet.

PKU is treated through a special diet that eliminates foods containing phenylalanine. Because most protein sources have this amino acid, the diet restricts foods like eggs, milk, meat, fish, beans, cheese, nuts and more. It is a lifelong diet that must be strictly adhered to, particularly during childhood development. For infants, breast milk is still allowed but must be supplemented with a formula specially made for children with PKU.

Some people may be helped by the drug sapropterin dihydrochloride, known as Kuvan. This medication provides BH4, a substance in the body that helps metabolize phenylalanine. The medication still needs to be taken in conjunction with the regimented diet.

5. If your child receives a PKU diagnosis, you’re not alone.

A diagnosis of PKU can feel overwhelming but treatment through diet has been proven effective. A specialist or your local doctor can provide you with the best frontline resources. For further information you can turn to national websites like these:

Phenylketonuria