The c.1054G>T variant in PAH is a missense variant predicted to cause substitution of glycine by cysteine at amino acid 352 (p.Gly352Cys). At least one patient with this variant displayed plasma phenylalanine concentration persistently above 120umol/L (2mg/dL) AND normal urine pterins and normal DHPR activity excluded a defect of BH4 cofactor metabolism, which is highly specific for PAH deficiency (PP4_Moderate, PMID 16601866). Of those individuals, one was compound heterozygous for the variant and a pathogenic variant confirmed in trans by parental testing (PM3). The highest population minor allele frequency in gnomAD v4.1.0 is 0.00001602 in the remaining population, which is lower than the ClinGen PAH Variant Curation Expert Panel threshold (<0.0002) for PM2_Supporting, meeting this criterion (PM2_Supporting). The computational predictor REVEL gives a score of 0.994, which meets the threshold of 0.932, evidence that correlates with strong impact to PAH function (PP3_Strong). Another missense variant c.1054G>C (p.Gly352Arg) [ClinVar Variation ID: 102496] in the same codon has been classified as likely pathogenic for PAH deficiency by the ClinGen PAH Variant Curation Expert Panel (PM5_Supporting). In summary, this variant meets criteria to be classified as pathogenic for autosomal recessive PAH deficiency based on the ACMG/AMP criteria applied, as specified by the ClinGen PAH Variant Curation Expert Panel: PP4_Moderate, PM2_supporting, PM3, PP3_strong, PM5_supporting (PAH VCEP specifications version 2.0.0; approved July 16, 2024).