Most babies with phenylketonuria (PKU) will appear healthy at birth.
Treated PKU
If dietary treatment is started within the first three weeks of life, people with PKU should not experience the severe learning difficulties that are associated with the condition.
Some children and adults with PKU do experience mild to moderate problems with certain high-level mental abilities and activities such as:
- attention
- planning
- problem solving
However, these problems are usually related to the increased blood phenylalanine level and will improve with stricter treatment.
There is also evidence that adults with PKU may be more likely to develop certain mental health problems at some point in their life compared with the population at large. The most widely reported conditions in people with PKU are:
- depression - feelings of extreme sadness that last for weeks or months
- anxiety disorders - feelings of unease, such as worry or fear, that can be mild or severe
- phobias, particularly agoraphobia - which is an intense fear of certain situations, such as being in crowded places or leaving home
- low self-esteem
It is uncertain whether the increased risk of developing these types of conditions is related to metabolic abnormalities, such as a reduction in the neurotransmitters (brain chemicals), which affect mood.
Alternatively, the increased risk of developing mental health conditions could be the result of the stress and anxiety that is caused by constantly having to worry about your diet. It may be that the increased risk is due to a combination of both of these factors.
Untreated PKU
A wide range of symptoms can occur if treatment for PKU is not started or delayed. The most common symptom of PKU is a learning disability. Usually, the longer treatment is delayed, the more severe the learning disability becomes.
Intelligence is measured using a type of test known as the intelligence quotient or IQ test. A person with average intelligence will score 100 in an IQ test (have an IQ of 100).
If a person with severe PKU is never treated, they will usually have an IQ score of less than 50 and require a lot of help with everyday activities. Even if PKU is not diagnosed on newborn screening, it is worth starting dietary treatment as it is sometimes possible to reverse some of the decline in intelligence. For example, in one case where a child’s treatment was delayed until they were two years of age, they went from having a moderate learning disability to having average intelligence.
Other symptoms of untreated PKU include:
- behavioural difficulties, such as frequent temper tantrums and episodes of self-harm
- very fair skin and hair
- eczema
- epilepsy - a condition that affects the brain and causes a person to have repeated fits (seizures)
