Symptoms

Newborns with PKU initially don't have any symptoms. However, without treatment, babies usually develop signs of PKU within a few months.

PKU signs and symptoms can be mild or severe and may include:

• A musty odor in the breath, skin or urine, caused by too much phenylalanine in the body
• Neurological problems that may include seizures
• Skin rashes (eczema)
• Fair skin and blue eyes, because phenylalanine can't transform into melanin — the pigment responsible for hair and skin tone
• Abnormally small head (microcephaly)
• Hyperactivity
• Intellectual disability
• Delayed development
• Behavioral, emotional and social problems
• Psychiatric disorders

Severity varies

The severity of PKU depends on the type.

• Classic PKU. The most severe form of the disorder is called classic PKU. The enzyme needed to convert phenylalanine is missing or severely reduced, resulting in high levels of phenylalanine and severe brain damage.
• Less severe forms of PKU. In mild or moderate forms, the enzyme retains some function, so phenylalanine levels are not as high, resulting in a smaller risk of significant brain damage.

But most children with the disorder still require a special PKU diet to prevent intellectual disability and other complications.

Pregnancy and PKU

Women who have PKU and become pregnant are at risk of another form of the condition called maternal PKU. If women don't follow the special PKU diet before and during pregnancy, blood phenylalanine levels can become high and harm the developing fetus or cause a miscarriage.

Even women with less severe forms of PKU may place their unborn children at risk by not following the PKU diet.

Babies born to mothers with high phenylalanine levels don't often inherit PKU. But they can have serious consequences if the level of phenylalanine is high in the mother's blood during pregnancy. Complications at birth may include:

• Low birth weight
• Delayed development
• Facial abnormalities
• Abnormally small head
• Heart defects and other heart problems
• Intellectual disability
• Behavioral problems

When to see a doctor

Seek medical advice in these situations:

• Newborns. If routine newborn screening tests show that your baby may have PKU, your child's doctor will want to start dietary treatment right away to prevent long-term problems.
• Women of childbearing years. It's especially important for women with a history of PKU to see a doctor and maintain the PKU diet before becoming pregnant and during pregnancy to reduce the risk of high blood phenylalanine levels harming their unborn babies.
• Adults. People with PKU continue to receive care across the life span. Adults with PKU who have stopped the PKU diet in their teens may benefit from a visit with their doctors. Returning to the diet may improve mental functioning and behavior and slow damage to the central nervous system that can result from high phenylalanine levels.