Phenylketonuria (PKU) overview
Types of Phenylketonuria (PKU)
Causes & genetic inheritance of Phenylketonuria (PKU)
Symptoms of Phenylketonuria (PKU)
PKU dietary management and treatment
Living with Phenylketonuria (PKU)
Phenylketonuria (PKU) overview
What is Phenylketonuria (PKU)?
Phenylketonuria, abbreviated as PKU, is a rare hereditary metabolic disorder diagnosed via neonatal screening. People with PKU cannot metabolise the amino acid phenylalanine (Phe). This is due to the enzyme phenylalanine hydroxylase (PAH) being very limited or completely absent. When the liver does not correctly process phenylalanine (Phe), the by-products of the malfunctioning protein breakdown process accumulate to toxic levels in the body. Left untreated, the toxic build-up of the unprocessed phenylalanine will lead to severe health complications such as developmental delays, neurological challenges, and potentially permanent brain damage. There is no cure for PKU. However, the disorder can be managed with a tailored low-protein diet, and phenylalanine blood levels can be controlled, preventing serious health complications and enabling a better quality of life.
Types of Phenylketonuria (PKU)
PKU manifests in different forms, with varying levels of severity. The most common form is classical PKU.
A milder variant is Hyperphenylalaninemia (HPA). In HPA, the enzyme phenylalanine hydroxylase functions somewhat, but is insufficient to break down Phe fully. Consequently, people with HPA have higher Phe tolerance levels than normal, but lower than those with classic PKU. A less strict low-protein diet is necessary, but regular monitoring and adjustment of the low-protein diet remain essential to prevent health problems.
Causes & genetic inheritance of Phenylketonuria (PKU)
PKU is an inherited disorder and is present from birth. Every cell contains DNA, half of which comes from the mother and half from the father. DNA contains genes that give instructions to the body. Sometimes, genes contain an error. If both parents are carriers of this gene change, that affects the enzyme phenylalanine hydroxylase, which degrades phenylalanine, there is a 1 in 4 (25%) chance with each pregnancy that their child will have PKU. However, because the gene change is uncommon, the overall chance of a child being born with PKU is low. PKU is diagnosed via neonatal screening.
Symptoms of Phenylketonuria (PKU)
Without dietary treatment, symptoms of PKU can be severe and varied. Common symptoms include:
- Intellectual disabilities
- Growth delays
- Behavioural problems
- Epileptic seizures
- Skin rash
- A musty smell of breath, skin, or urine
The importance of early detection through newborn screening, usually through a heel prick test is crucial.
PKU dietary management and treatment
Living with PKU requires constant vigilance and commitment to a low-protein diet supported by regular medical check-ups.
The role of Food for Special Medical Purposes and protein substitutes
A low-protein diet is crucial for people with PKU and other metabolic disorders. The PKU diet is specially designed to limit the intake of phenylalanine, which helps keep their blood Phe levels low and prevents the harmful effects of their accumulation. The PKU diet consists mainly of protein-restricted foods, supplemented with specialised amino acid preparations to ensure the body receives enough of the other essential amino acids. Precisely following this diet is critical for proper development.
Beyond adhering to a low-protein diet, PKU is managed with a variety of supplementary amino acids and protein substitutes that supply essential nutrients according to phenylalanine tolerance levels and nutritional needs. These products should be used under medical supervision and prescribed by a doctor or dietitian
Medical intervention
While dietary management is the cornerstone of PKU treatment, ongoing research explores other avenues. Advances in gene therapy and enzyme replacement are being investigated as potential future PKU treatments.
PKU diet and foods to avoid
The PKU diet focuses on limiting phenylalanine intake. This means consuming a diet mainly of low-phenylalanine foods such as fruits, vegetables, and specially formulated low-protein products. It is crucial to track phenylalanine intake diligently.
Foods high in phenylalanine to avoid include:
- Meat
- Fish
- Dairy
- Nuts
Living with Phenylketonuria (PKU)
Living with PKU requires constant vigilance and commitment to a low-protein diet, supported by regular medical check-ups. It's essential to have ongoing support from a dietician specialising in metabolic disorders to help manage a low-protein diet and ensure the correct amount of protein substitute is prescribed to ensure protein requirements are still met.
PKU presents different challenges throughout life. As a baby, child, teenager and adult, the needs and experiences of a person diagnosed with PKU will vary. For example, babies need a special infant feed, in addition to breast milk and/or standard infant formula, children must learn to cope with dietary restrictions, teenagers may face social pressure, and adults must manage their diet while living an independent, busy lifestyle.
Regular check-ups with a doctor and/or dietitian are crucial to ensure ongoing effective management of the disorder as the body's needs change over time. By following a low-protein diet and appending medical protocols, people with PKU can live healthy and full lives. For inspiration, visit the low-protein recipes page (link to page) for a list of delicious sweet and savoury recipes.
