The NM_000156.6:c.670G>A variant in GAMT is a missense variant that is predicted to result in the substitution of alanine by threonine at amino acid 224 (p.Ala224Thr). The highest population minor allele frequency in gnomAD v2.1.1 is 0.00034 (12/35338 alleles) in the Latino population, which is lower than the ClinGen CCDS VCEP’s threshold for PM2_Supporting (<0.0004), meeting this criterion (PM2_Supporting). The computational predictor REVEL gives a score of 0.147 which is below the threshold of 0.5, evidence that does not predict a damaging effect on GAMT function (BP4). Expression of the variant in GAMT-deficient fibroblasts showed that it resulted in similar GAMT enzymatic activity to wild-type (BS3_Supporting). There is a ClinVar entry for this variant (Variant ID: 205593). In summary, this variant meets the criteria to be classified as likely benign for GAMT deficiency. Although there are both pathogenic and benign types of evidence for this variant, the pathogenic evidence is not considered inconsistent with the final classification. GAMT-specific ACMG/AMP criteria applied, as specified by the ClinGen CCDS VCEP (Specifications Version 1.1.0): PM2_Supporting, BS3_Supporting, BP4. (Classification approved by the ClinGen CCDS VCEP on February 23, 2023).