What is phenylketonuria?
A rare but potentially dangerous hereditary condition is phenylketonuria (PKU). Protein from foods like meat and fish is broken down by our bodies into amino acids, which are the "building blocks" of protein. Our own proteins are then produced from these amino acids. Any amino acids that are surplus to requirements are further broken down and eliminated from the body. Phenylalanine accumulates in blood and the brain in PKU patients because they are unable to break it down. The result could be brain damage.
History
An inherited mistake in phenylalanine metabolism is phenylketonuria (PKU). In Norway in 1934, Asbjörn Fölling gave the first account of it. The example of inherited metabolic diseases has been PKU. Additionally, it made possible the first biological theory to explain mental impairment. This led to widespread use of newborn screening to look for this disease in infants. Contrary to industrialized nations, PKU is still a factor in mental retardation in Mexico; for this reason, it's critical to understand the problem's history, the impact of PKU in Mexico, and potential solutions.
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Epidemiology of PKU
PKU is most commonly diagnosed in neonates because of newborn screening programs. Consider PKU at any age in an individual with developmental delay or intellectual disability because infants are missed by newborn screening programs on rare occasions.
No s*x predilection is known. Women with PKU must restrict their phenylalanine levels during pregnancy to avoid birth defects and intellectual disability in their infants. Untreated PKU during pregnancy can result in maternal PKU syndrome, which can variably cause congenital heart defects, brain malformations, microcephaly, and intellectual impairment. In the United States, PKU is most common in whites. Worldwide, PKU is most common in whites and Asians.
Risk factors of phenylketonuria
Risk factors for inheriting phenylketonuria include:
Having two parents with a defective PKU gene: Both parents must pass along a copy of the mutated PKU gene for their child to develop the condition.
Being of certain ethnic decent: The gene defect varies by ethnic groups and is less common in African-Americans than in other ethnic groups.
Children of mothers with PKU who didn’t follow the PKU diet during pregnancy are at risk of birth defects due to the high levels of phenylalanine in their mothers’ blood.
Causes of phenylketonuria
PKU is an inherited condition caused by a defect in the PAH gene. The PAH gene helps create phenylalanine hydroxylase, the enzyme responsible for breaking down phenylalanine. A dangerous buildup of phenylalanine can occur when someone eats high-protein foods, such as eggs and meat. Both parents must pass on a defective version of the PAH gene for their child to inherit the disorder. If just one parent passes on an altered gene, the child won’t have any symptoms, but they’ll be a carrier of the gene.
Symptoms
PKU doesn’t usually cause any symptoms if treatment is started early. Without treatment, PKU can damage the brain and nervous system, which can lead to learning disabilities.
Other symptoms of untreated PKU include:
Behavioural difficulties – such as frequent temper tantrums and episodes of self-harm
Fairer skin, hair and eyes than siblings without the condition (phenylalanine is involved in the body’s production of melanin, the pigment responsible for skin and hair color)
Eczema
Recurrent vomiting
Jerking movements in arms and legs
Tremors
Epilepsy
Musty smell on the breath, skin and urine
Diagnosis and test
PKU can be easily detected with a simple blood test. All states in the United States require a PKU screening test for all newborns as part of the newborn screening panel. The test is generally done by taking a few drops of blood from the baby before the baby leaves the hospital.
If the screening test is positive, further blood and urine tests are required to confirm the diagnosis. Genetic testing is also done.
Treatment and medications
The main treatment for phenylketonuria includes:
A lifetime diet with very limited intake of protein, because foods with protein contain phenylalanine
Taking a PKU formula — a special nutritional supplement — for life to make sure you get enough essential protein (without phenylalanine) and nutrients that are crucial for growth and general health.
A safe amount of phenylalanine differs for each person with PKU and can vary over time. In general, the idea is to consume only the amount of phenylalanine that’s necessary for normal growth and body processes, but no more. Your doctor can determine a safe amount through:
Regular review of diet records, growth charts and blood levels of phenylalanine
Frequent blood tests that monitor PKU levels as they change over time, especially during childhood growth spurts and pregnancy
Other tests that may be done to assess growth, development and health.
Phenylketonuria prevention
If you're a phenylketonuric woman thinking about having a child:
Maintain a low-phenylalanine diet: Before getting pregnant, women with PKU can reduce the risk of birth abnormalities by maintaining (or resuming) a low-phenylalanine diet. Before beginning your in vitro fertilization journey, PKU-positive women should speak with their doctor.
Preconception genetic counseling may be helpful if you have a family history of PKU, a close relative who has the condition, or a kid who has it. You can learn more about how PKU is passed down through your family tree from a specialist who specializes in medical genetics. Additionally, he or she can support family planning and assist in determining your risk of passing on PKU to future generations.
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