Mild Hyperphenylalaninaemia

This is a benign form of phenylalanine hydroxylase deficiency that does not require therapy as Phe concentrations do not exceed certain thresholds (Phe <600 µmol/l in Germany/Austria/Switzerland, <400 µmol/l in the UK, <360 µmol/l in the USA). It is associated with at least one high residual activity "MHP variant" on one allele of the PAH gene.