Phenylketonuria, one of the most common inherited diseases of amino acid metabolism, is caused by a defect in the phenylalanine hydroxylase (PAH) gene, and approximately 13% of the mutations affect conserved 3’ and 5’ splice sites, and are thus recognized as causing splicing defects (HGMD Professional Release 2017.1). This evidence concerns the gene PAH and phenylketonuria.