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What is PKU (Phenylketonuria)?

PKU stands for phenylketonuria. It is an inherited metabolic condition that affects how babies, teens and adults break down protein. Many foods contain protein, which the body needs for growth and repair. Proteins are broken down into amino acids, the building blocks of protein, by enzymes that function like chemical scissors. These enzymes then break the amino acids into smaller parts as part of metabolism, encompassing the chemical processes occurring inside the body's cells. With PKU, the body lacks an enzyme called phenylalanine hydroxylase, resulting in the inability to break down an amino acid called phenylalanine. Consequently, toxic levels of phenylalanine build up in the blood and brain. Therefore, individuals diagnosed with PKU must adhere to a lifelong PKU diet to manage their condition effectively. 

Incidence, Genetics and how to test for PKU:

PKU, occurring in just 1 in 10,000-15,000 newborns, is diagnosed through newborn screening by identifying high levels of phenylalanine in the blood. This inherited condition involves both parents contributing a non-working PKU gene to their child. Carriers possessing one functional gene don't have PKU themselves. In pregnancies where both parents are carriers, risks include a 25% chance of PKU, a 50% chance of the baby being a carrier, and a 25% chance of the baby having two functional genes, neither having PKU nor being a carrier. Unfortunately, there is no preventive measure for PKU, given the non-functionality of both genes responsible for the phenylalanine hydroxylase enzyme. The cornerstone of managing PKU symptoms involves adhering to a strict low-protein diet, commonly known as the PKU diet, which limits the intake of phenylalanine. Managing phenylalanine during pregnancy and using a supplementary formula for phenylketonuria is crucial to managing PKU.

Symptoms of PKU

PKU patients must adhere to a low-protein diet meticulously to manage PKU symptoms and maintain good overall health. Delayed diagnosis may heighten the risk of permanent intellectual and physical disability because of the metabolic dysfunction caused by PKU. In instances where a diagnosed PKU patient undergoes treatment without dietary adherence or inconsistent dietary adherence, there is a high likelihood that the patient will experience ongoing PKU symptoms, which severely impact the overall quality of life, health, and life expectancy.

Management for PKU

PKU management involves a special diet that limits the consumption of high-protein foods. The diet needs measured amounts of phenylalanine-containing foods and incorporates protein substitutes essential for metabolic control. Foods high in phenylalanine, such as meat, fish, eggs, cheese, bread, pasta, nuts, seeds, soya, tofu, and aspartame, must be avoided. Please consult your care team for a PKU-friendly list of foods. Babies receive a restricted amount of phenylalanine from breast milk or measured PKU infant formula, monitored regularly by a metabolic dietitian. Low-protein foods, including most fruits and vegetables, are the cornerstones of a healthy PKU diet. Complementary foods such as low-protein bread, low-protein pasta and scripted supplements like low-protein formulas and amino acids are excellent energy sources and enable dietary variety. Adults with PKU must continue adhering to the PKU diet throughout their lives. 

During any childhood illness, catabolism (a protein breakdown) occurs, increasing blood phenylalanine levels. Maintaining a low-protein diet during these periods is crucial to prevent the escalation of phenylalanine levels. Each patient's protein tolerance levels are different and can fluctuate over time. Therefore, PKU monitoring includes frequent blood tests for phenylalanine, height and weight assessments, developmental checks, and ongoing personalised dietary adjustments based on age, weight, and phenylalanine levels. For pregnant individuals with PKU, managing phenylalanine intake is crucial to ensure a healthy pregnancy. Adherence to the prescribed PKU diet contributes to better health outcomes. It supports the overall well-being of individuals with PKU, influencing factors such as phenylketonuria life expectancy.

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