Comprehensive nationwide screening for PKU began in 1969.  This means that many individuals with PKU born prior to nationwide screening were not diagnosed until damage to the brain was evident. Consequently, many individuals with PKU have spent their lives in social care environments or at home needing constant supervision.

In addition to learning difficulties, high blood phenylalanine levels may cause other problems. Some individuals exhibit behavioural problems, for example – aggressiveness, hyperactivity, self-injurious behaviour, sleep problems and they may also suffer from skin conditions such as eczema.

Guidance on the treatment of people with untreated/late treated PKU is contained in the consensus European Guidelines.