Phenylketonuria (PKU) happens when a chemical called phenylalanine cannot be processed by the body. Phenylalanine is an amino acid that occurs naturally in the body. Amino acids are the chemicals that make up proteins within the body. Phenylalanine requires a protein called phenylalanine hydroxylase to break it down.
PKU occurs in people who have a genetic mutation that causes abnormal production of phenylalanine hydroxylase. In people with PKU, phenylalanine can build up to dangerous levels. Foods with high levels of protein or artificial sweeteners usually have phenylalanine in them.
PKU can be considered mild, moderate, or severe based on the individual case.
Common symptoms of PKU include:
PKU can be diagnosed at birth. As soon as PKU is diagnosed, treatment should begin, preventing these symptoms. If you have a newborn or infant, it’s important to get them screened for PKU.
PKU is caused by a mutation in the phenylalanine hydroxylase (PAH) gene. The PAH gene is used to process the amino acid phenylalanine. When the PAH gene is mutated, phenylalanine cannot be correctly processed in the body and builds up.
Eventually, the buildup of phenylalanine will start to affect the brain, causing symptoms like delayed development. When both copies of the PAH gene are mutated- the copy from the mother and the copy from the father- a child will be born with PKU. An individual can live with one mutated copy of the PAH gene without developing PKU.
Risk factors for PKU include having parents with PKU or parents with one mutated copy of the PAH gene. An additional risk factor, although minimal, is being of European descent. People of European descent develop PKU at a greater prevalence than anyone else in the world.
PKU is typically diagnosed during a newborn screening. However, this service may not always be offered where you deliver. PKU can easily be diagnosed shortly after birth at a routine health checkup. A doctor will perform a blood test or a urine test to check for abnormally high levels of phenylalanine. If they’re detected, a genetic test can be done to confirm the diagnosis.
Complications of PKU occur if it goes undiagnosed or untreated. They include permanent brain damage, seizures or tremors, lifelong social, emotional, and behavioural issues, and complex health issues. Another complication to consider if you live with PKU is pregnancy. Individuals with PKU can carry a baby safely to term, but it’s important to see an obstetrician who is familiar with treating mothers who have PKU and other genetic conditions.
Staying on a diet low in phenylalanine during pregnancy will not only protect you, it will prevent harm to the foetus. High levels of phenylalanine in a pregnant mother can be harmful to a developing foetus.
There is no cure for PKU, and it does need to be managed throughout one’s life. However, it can be safely and effectively managed through dietary changes or medications. Medication options can give your body a synthetic form of the phenylalanine hydroxylase enzyme that breaks down phenylalanine, allowing you to live without dietary restrictions.
There is also a medication option that can be taken in conjunction with dietary restrictions. It helps break down phenylalanine as well, but it does not replace the phenylalanine hydroxylase enzyme and must be used with dietary restrictions.
You can discuss these two options with your doctor.
Additionally, eating a diet low in phenylalanine can be an efficient way to manage PKU. This usually looks like a low-protein diet complemented with vitamins and supplements. Consider consulting a dietician to make sure you’re getting the nutrients your body needs.