This pattern of inheritance is called autosomal recessive. Inheritanceįor a child to inherit PKU, both the mother and father must have and pass on the changed gene. In a person with PKU, a change in the phenylalanine hydroxylase (PAH) gene causes a lack of or reduced amount of the enzyme that's needed to process phenylalanine, an amino acid.Ī dangerous buildup of phenylalanine can develop when a person with PKU eats protein-rich foods, such as milk, cheese, nuts or meat, or grains such as bread and pasta, or aspartame, an artificial sweetener. They have a 25% chance of having an affected child with two changed genes.Ī gene change (genetic mutation) causes PKU, which can be mild, moderate or severe. They have a 50% chance of having an unaffected child who also is a carrier. Two carriers have a 25% chance of having an unaffected child with two unaffected genes. The parents' health is rarely affected because they have only one changed gene. In an autosomal recessive disorder, two changed genes are inherited, one from each parent. Returning to the diet may improve mental functioning and behavior and prevent further damage to the central nervous system that can result from high phenylalanine levels. Adults with PKU who have stopped the PKU diet in their teens may benefit from a visit with their health care providers. People with PKU need to receive lifelong care. This reduces the risk of high blood phenylalanine levels harming their unborn babies. It's especially important for women with a history of PKU to see a health care provider and maintain the PKU diet before becoming pregnant and during pregnancy. If routine newborn screening tests show that your baby may have PKU, your child's health care provider will want to start dietary treatment right away to prevent long-term problems. Talk to your health care provider in these situations: In addition, maternal PKU can cause the child to have delayed development, intellectual disability and problems with behavior. But a child can have serious problems if the level of phenylalanine is high in the mother's blood during pregnancy. If women don't follow the special PKU diet before and during pregnancy, blood phenylalanine levels can become high and harm the developing baby.Įven women with less severe forms of PKU may place their unborn children at risk by not following the PKU diet.īabies born to women with high phenylalanine levels don't often inherit PKU. Women who have PKU and become pregnant are at risk of another form of the condition called maternal PKU. Regardless of the form, most infants, children and adults with the disorder still require a special PKU diet to prevent intellectual disability and other complications. In mild or moderate forms, the enzyme still has some function, so phenylalanine levels are not as high, resulting in a smaller risk of significant brain damage. This results in high levels of phenylalanine that can cause severe brain damage.
The enzyme needed to break down phenylalanine is missing or severely reduced. The most severe form of the disorder is called classic PKU.
A musty odor in the breath, skin or urine, caused by too much phenylalanine in the body.Signs and symptoms of untreated PKU can be mild or severe and may include: However, without treatment, babies usually develop signs of PKU within a few months. Newborns with PKU initially don't have any symptoms.