GCH1 and phenylketonuria: For the 209 true PKU negatives, newborn sample S-119 was identified as a heterozygote carrier of the pathogenic PAH variant c.1064C > A and the remaining 208 newborns did not carry any PAH variants or other variants in the PTS, GCH1, PCBD1 and QDPR genes associated with BH4 deficiency.