The NM_001482.3:c.1037C>T variant in GATM is a missense variant predicted to cause substitution of proline by leucine at amino acid 346 (p.Pro346Leu). To our knowledge, this variant has not been reported in the literature in any individuals with AGAT deficiency. The highest population minor allele frequency in gnomAD v2.1.1 is 0.000009 (1/113704 alleles) in the non-Finnish European population, which is lower than the ClinGen LSD VCEP’s threshold for PM2_Supporting (<0.000055), meeting this criterion (PM2_Supporting). Expression of the variant in HeLa cells resulted in <10% wild type AGAT activity indicating that this variant may impact protein function (PMID 27233232)(PS3_Supporting). The computational predictor REVEL gives a score of 0.237 which is neither above nor below the thresholds predicting a damaging (>0.75) or benign (<0.15) impact on AGAT function. In summary, this variant meets the criteria to be classified as uncertain significance for AGAT deficiency based on the ACMG/AMP criteria applied, as specified by the ClinGen Cerebral Creatine Deficiency Syndromes Variant Curation Expert Panel (Specifications Version 1.1.0): PM2_Supporting, PS3_Supporting. (Classification approved by the ClinGen CCDS VCEP on January 24, 2023).