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To have an autosomal recessive disorder, you inherit two mutated genes, one from each parent. These disorders are usually passed on by two carriers. Their health is rarely affected, but they have one mutated gene recessive gene and one normal gene dominant gene for the condition. A defective gene genetic mutation causes PKU, which can be mild, moderate or severe.
In a person with PKU, this defective gene causes a lack of or deficiency of the enzyme that's needed to process phenylalanine, an amino acid. A dangerous buildup of phenylalanine can develop when a person with PKU eats protein-rich foods, such as milk, cheese, nuts or meat, and even grains such as bread and pasta, or eats aspartame, an artificial sweetener.
This buildup of phenylalanine results in damage to nerve cells in the brain. For a child to inherit PKU, both the mother and father must have and pass on the defective gene. This pattern of inheritance is called autosomal recessive. It's possible for a parent to be a carrier — to have the defective gene that causes PKU, but not have the disease.
If only one parent has the defective gene, there's no risk of passing PKU to a child, but it's possible for the child to be a carrier. Most often, PKU is passed to children by two parents who are carriers of the disorder, but don't know it. Untreated PKU can lead to complications in infants, children and adults with the disorder.
When mothers with PKU have high blood phenylalanine levels during pregnancy, fetal birth defects or miscarriage can occur. Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission. This content does not have an English version. This content does not have an Arabic version. Overview Phenylketonuria fen-ul-key-toe-NU-ree-uh , also called PKU, is a rare inherited disorder that causes an amino acid called phenylalanine to build up in the body.
Email address. This means a baby needs to receive 2 copies of the mutated gene to develop the condition — 1 from their mother and 1 from their father. If you're a carrier of the altered gene and you have a baby with a partner who's also a carrier, your baby has:. Many adults with PKU find they function best while on a low-protein diet. The current advice is for people with PKU to remain on a low-protein diet for life.
Unlike in young children, there is not yet any evidence that high phenylalanine levels cause any permanent brain damage in adults with PKU. Some adults with PKU may have higher phenylalanine levels because they find it difficult to follow the low-protein diet or have returned to a normal diet. As a result, they may find they do not function as well.
For example, they may lose concentration or have a slower reaction time. These adverse effects can usually be reversed by going back on to a strict diet to bring the phenylalanine levels down again. Anyone who returned to a normal diet should still be supported by their clinicians and have a regular follow-up to monitor their condition for any complications that might arise. For women with PKU, it's essential that they return to a strict diet if they're considering becoming pregnant, as high phenylalanine levels can harm an unborn child.
Women with PKU must take particular care during pregnancy, as high levels of phenylalanine can damage their unborn baby. Provided that phenylalanine levels are strictly controlled during pregnancy, problems can be avoided and there's no reason why a woman with PKU should not be able to have a normal, healthy baby.
It's recommended that all women with PKU plan their pregnancies carefully. You should aim to follow a strict low-protein diet and monitor your blood twice a week before becoming pregnant. It's best to try to conceive once phenylalanine levels are within the target range for pregnancy. During pregnancy, you'll be asked to provide blood samples 3 times a week and will be in frequent contact with a dietitian. As soon as your baby is born, phenylalanine control can be relaxed and there's no reason why you cannot breastfeed your baby.
Contact your PKU doctor and dietitian as soon as possible if you become pregnant when your phenylalanine levels are not adequately controlled. If your phenylalanine levels can be brought under control within the first few weeks of your pregnancy, the risk of damage to your baby should be small.
But your pregnancy will need to be monitored very carefully. People affected by PKU have difficulty breaking down phenylalanine Phe , an amino acid found in all natural protein. PAH breaks down Phe into another amino acid called tyrosine. Since Phe is found in many foods, such as chicken, meat, eggs, dairy, nuts, grains, and legumes, people with PKU typically eat a special diet.
The signaling molecules that brain cells use to communicate with each other are called neurotransmitters. When neurotransmitters are not made in the right amounts, the brain cannot function properly. High blood Phe levels can cause disruptions in neurotransmitters like serotonin and dopamine, which are important for mood, learning, memory, and motivation. In addition to disrupting neurotransmitter balance, Phe itself can be directly toxic to the brain.
Scientists think that these changes are behind how high blood Phe affects the way a person thinks, feels, and acts. When Phe levels are high or uncontrolled, people with PKU can experience symptoms that have lasting impacts on the brain.
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