What is phenylketonuria (PKU)?
Phenylketonuria is a hereditary metabolic disorder Overview of Hereditary Metabolic Disorders Your body breaks down food you eat into simple chemical building blocks. Then your body uses those building blocks to make other substances your body needs to grow and repair itself. This whole... read more . Children with PKU are born without the enzyme needed to break down phenylalanine. Phenylalanine is an amino acid (the building blocks of proteins) in many foods and drinks. Normally, your body breaks down and gets rid of extra phenylalanine. Children with PKU can't make the enzyme that is needed to break down phenylalanine to get rid of it.
If PKU isn't treated, phenylalanine builds up in the blood and causes brain problems (intellectual disability Intellectual Disability Intellectual disability is a brain problem that results in lower than normal intelligence. It can happen as your baby's brain develops in your womb. The disability can be mild or more severe... read more )
Children with PKU must stay on a lifelong special diet that has very little phenylalanine in it
What causes PKU?
Having 2 defective PKU genes causes PKU. If you have 2 defective PKU genes, you can't make an enzyme that breaks down phenylalanine.
PKU happens when both parents pass the defective gene that causes PKU to a child
If only one parent has the defective PKU gene and the other parent doesn't, the child can't have PKU
If both parents have don't have PKU but have one copy of the defective PKU gene (are carriers), the child has a 1 in 4 chance of having PKU
What are the symptoms of PKU?
Babies don't usually have symptoms of PKU right away, although sometimes they are sleepy or don't eat well. Symptoms in untreated children usually develop over a few months after birth and include:
Sometimes, a musty body smell
As untreated children get older, their brain doesn't develop as it should (they have intellectual disability Intellectual Disability Intellectual disability is a brain problem that results in lower than normal intelligence. It can happen as your baby's brain develops in your womb. The disability can be mild or more severe... read more ). They may become aggressive or hyperactive.
Children who are treated in the first few days of life do not develop the severe symptoms of PKU. A phenylalanine-restricted diet, if started early and maintained well, allows for mostly normal development.
How can doctors tell if my child has PKU?
Doctors test all newborn babies for PKU as part of normal newborn screening Newborn Screening Tests Screening tests are done to detect health conditions that are not yet causing symptoms. Many serious disorders that are not apparent at birth can be detected by various screening tests. Early... read more . This includes a blood test using a few drops of blood from the baby's heel.
If PKU runs in your family, doctors can do testing before the baby is born (prenatal testing Prenatal Diagnostic Testing Prenatal diagnostic testing involves testing the fetus before birth (prenatally) to determine whether the fetus has certain abnormalities, including certain hereditary or spontaneous genetic... read more , such as amniocentesis Amniocentesis Prenatal diagnostic testing involves testing the fetus before birth (prenatally) to determine whether the fetus has certain abnormalities, including certain hereditary or spontaneous genetic... read more ) to see if the baby has PKU.
You can get a blood test to find out if you're a carrier of the PKU gene.
How do doctors treat PKU?
Starting in the first few weeks of a baby's life, the baby must go on a diet nearly free of phenylalanine. Doctors treat PKU with:
A strict diet that limits phenylalanine
Sometimes, medicine to increase tolerance of phenylalanine
People with PKU can't eat any milk, meat, or other foods with protein. They can have some fruits, vegetables, and grain cereals. They also eat special food, such as phenylalanine-free formula and nutritional products. Your child's doctor will tell you what your child can eat.