The NM_000277.3:c.125AAG[2] variant in PAH is predicted to cause a change in the length of the protein due to an in-frame deletion of 1 amino acid in a non-repeat region (p.Glu44del) (PM4). This variant has been detected in at least 3 unrelated individuals with PAH deficiency (PMID: 28982351, PMID: 26600521, PMID: 9012412). Of these individuals, one was a compound heterozygote for the variant and a pathogenic variant, p.Arg408Trp, in trans (phase confirmed by parental testing) (PMID: 26600521), and one was a compound heterozygote for the variant and a likely pathogenic variant, p.Met276Arg, in trans (phase confirmed by parental testing) (PMID: 28982351) (2pts total, PM3_Strong). These two individuals had plasma phenylalanine >120 μmol/L and exclusion of a defect of BH4 cofactor metabolism (PMID: 28982351, PMID: 26600521). These two individuals had plasma phenylalanine >120 μmol/L and exclusion of a defect of BH4 cofactor metabolism (PMID: 28982351, PMID: 26600521). The highest population minor allele frequency in gnomAD v2.1.1 is 0.000096 (1/10368 alleles) in the Ashkenazi Jewish population, which is lower than the ClinGen PAH VCEP’s threshold for PM2_Supporting (<0.0002), meeting this criterion (PM2_Supporting). There is a ClinVar entry for this variant (Variation ID: 102594, 1 star review status) with one submitter classifying the variant as likely pathogenic and 3 submitters classifying the variant as a variant of uncertain significance. In summary, this variant meets the criteria to be classified as likely pathogenic for PAH deficiency based on the ACMG/AMP criteria applied, as specified by the ClinGen PAH Variant Curation Expert Panel (Specifications Version 2.0): PM2_Supporting, PM3_Strong, PM4, PP4_Moderate.