The NM_001482.3(GATM):c.505C>T (p.Arg169Ter) variant in GATM is a nonsense variant predicted to cause a premature stop codon in biologically-relevant-exon 4/9 leading to nonsense mediated decay in a gene in which loss-of-function is an established disease mechanism (PVS1). This variant is reported to be homozygous in a proband and sibling, both of whom have undetectable GAA in plasma and urine, and reduced creatine peak (about 2/3 normal) on brain MRS with elevated NAA/creatine ratio (PMID 20625172, 23660394, 26490222)(PP4_Strong, PM3_Supporting). The highest population minor allele frequency in gnomAD v2.1.1 is 0.00005 in the East Asian population. This is lower than the ClinGen CCDS VCEP's threshold for PM2_Supporting (<0.000055) meeting this criterion (PM2_Supporting). There is a ClinVar entry for this variant (Variation ID: 55919). In summary, this variant meets the criteria to be classified as pathogenic for AGAT deficiency. GATM-specific ACMG/AMP codes met, as specified by the ClinGen Cerebral Creatine Deficiency Syndromes VCEP (Specifications Version 1.1.0): PVS1, PP4_Strong, PM3_Supporting, PM2_Supporting. (Classification approved by the ClinGen CCDS VCEP on June 6, 2022).