Commonly referred to as PKU, this is a metabolic cause of learning disability. The incidence in Europeans is around 1 in 15,000 births. It is due to the inability of the baby to metabolise the amino acid, phenylalanine (see AMINO ACIDS). In many countries, every newborn baby is screened for PKU by testing a spot of their blood. A positive diagnosis leads to lifelong treatment with a diet low in phenylalanine, with a good chance that the infant will grow up without learning disability. (See also METABOLIC DISORDERS; GENETIC DISORDERS – Recessive genes.)