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Phenylketonuria

Phenylketonuria (commonly known as PKU) is an inherited disorder that increases the levels of a substance called phenylalanine in the bloodstream (an amino acid that is obtained through diet). It is found in all proteins and in some artificial sweeteners. If PKU is not treated, phenylalanine can build up to harmful levels in the body, causing intellectual disability and other serious health problems.

Diagnosis: screening and testing for PKU

Most cases of PKU are now detected soon after birth through the newborn blood spot test. This involves collecting a drop of blood from the baby's heel and testing it for abnormalities that could indicate PKU. More tests will be needed to confirm the diagnosis.

PKU occurrence varies among ethnic groups and geographic regions worldwide. Most cases of PKU are now detected shortly after birth by newborn screening, and treatment is started promptly. As a result, the severe signs and symptoms of classic PKU are rarely seen.

Symptoms:

PKU signs and symptoms may range be from mild to severe:

  • Classic PKU: the most severe form of this disorder is known as classic PKU, where infants appear normal until they are a few months old. Without treatment, these children develop permanent intellectual disability seizures, delayed development and behavioural problems while psychiatric disorders are also common. Untreated children may have a musty or mouse-like odour as a side effect of excess phenylalanine in the body. Children with classic PKU tend to have lighter skin and hair than unaffected family members and are also likely to have skin disorders such as eczema.
  • Less severe forms of this condition, variant PKU and non-PKU hyperphenylalaninemia, have lower risk of brain damage.  People with very mild cases may not need treatment if they follow a low-phenylalanine diet.
  • Babies born to mothers with PKU and uncontrolled phenylalanine levels (women who no longer follow a low-phenylalanine diet) have a significant risk of intellectual disability because they are exposed to very high levels of phenylalanine before birth. These infants may also have a low birth weight and grow slower than other children. Other characteristic medical problems include heart defects or other heart problems, an abnormally small head size (microcephaly), and behavioral problems. Women with PKU and uncontrolled phenylalanine levels also have an increased risk of pregnancy loss.

Treatments:

There is no cure for PKU, but treatment can prevent intellectual disabilities and other health problems.  A person with PKU should receive treatment at a medical center, that specialised in the disorder.

The PKU diet: people with PKU need to follow a diet that limits foods with phenylalanine. The diet should be followed carefully and started as soon after birth as possible. Experts used to believe it was safe for people to stop following the diet as they got older. However, they now recommend that people with PKU stay on the diet throughout their lives for better physical and mental health.

It is especially important for a pregnant woman with PKU to strictly follow the low-phenylalanine diet throughout her pregnancy to ensure the healthy development of her infant.

People with PKU need to control various high-protein foods, i.e milk and cheese, eggs, nuts, legumes, meat and fish. Often, people with PKU also have to limit their intake of lower-protein foods, such as certain fruits and vegetables. However, a PKU diet can include low-protein special product, e.g. bread, flour etc.

People with PKU also need to avoid aspartame, an artificial sweetener, which is contained in some foods, drinks, medications, and vitamins. Aspartame releases phenylalanine when it is digested, thereby raising the level of phenylalanine in the blood.

The safe phenylalanine rate to consume differs for each person. Thus, a person with PKU needs to work with a health care professional to develop an individualised diet. The goal is to eat only the right amount of phenylalanine needed for healthy growth and body processes but not any extra. Frequent blood tests and doctor visits are necessary to help determine how well the diet is working. 

However, the PKU diet can be very challenging. Getting support from friends and family or a support group can help. Sticking with the diet ensures better functioning and improved overall health.

A PKU Formula: people who follow the PKU diet will not get enough essential nutrients from food. Therefore, they must add a special formula.

Newborns diagnosed with PKU should receive special infant formula. The formula may be mixed with a small amount of breast milk or regular infant formula to make sure the child gets enough phenylalanine for normal development but not enough to cause harm.

Older children and adults should consume a different formula adapted to meet their nutritional needs, every day throughout their life.

In addition to the formula, health care professionals may recommend other supplements. For example, omega 3 fatty acids may be recommended to help with fine motor coordination and other aspects of development.