The NM_000152.5:c.1913G>T variant in GAA is predicted to result in the substitution of glycine by valine at amino acid 638 (p.Gly638Val). At least 4 patients diagnosed with Pompe disease have been reported with this variant. This includes three patients with symptoms consistent with infantile onset Pompe disease (including cardiac hypertrophy and hypotonia), and treated with enzyme replacement therapy, two of whom also had documented values showing very low GAA activity (PMID: 15121988, 19588081, 24715333, 29573408, 30049495, 32888769, 38524130), (PP4_Moderate). Four patients have been reported to be compound heterozygous for the variant and another variant in GAA that has been classified as pathogenic or likely pathogenic by the ClinGen LD VCEP including c.307T>G (p.Cys103Gly) (ClinVar Variation ID: 92483, SCV002817442.1) (PMID: 38524130, phase unknown, 0.5 points), c.-32-13T>G (ClinVar Variation ID: 4027) (PMID: 19588081, phase unknown, 0.5 points)), c.1548G>A (p.Trp516Ter) (ClinVar Variation ID: 189025, SCV001371740.1 (PMIDs: 15121988, 24715333, 29573408, 30049495, 32888769, phase unknown, 0.5 points), and c.1912G>T (p.Gly638Trp) (PMID: 19588081, confirmed in trans, 1 point). Total 2.5 points (PM3_Strong). When expressed in HEK293 cells, the variant result in no GAA activity, and was incorrectly processed remaining as the precursor 100kD band on Western blot of cellular protein (PMID: 24715333) (PS3_Moderate). The computational predictor REVEL gives a score of 0.986 which is above the threshold of 0.7, evidence that correlates with impact to GAA function (PP3). Another missense change at the same amino acid position, c.1912G>T (p.Gly638Trp) has been classified as pathogenic by the ClinGen LD VCEP (PM5). This variant is absent in gnomAD v2.1.1 (PM2_Supporting). In gnomAD v4.1, the highest population minor allele frequency is 0.000003394 (4/1178708 alleles) in the European non-Finnish population population, which is lower than the ClinGen Lysosomal Diseases VCEP’s threshold for PM2_Supporting (<0.001), also meeting this criterion. Another missense change at the same amino acid position, c.1912G>T (p.Gly638Trp) has been classified as pathogenic by the ClinGen LD VCEP (PM5). There is a ClinVar entry for this variant (Variation ID: 928930). In summary, this variant meets the criteria to be classified as a pathogenic variant for Pompe disease. GAA-specific ACMG/AMP criteria applied, as specified by the ClinGen Lysosomal Diseases VCEP (Specifications Version 2.0): PM3_Strong, PM5, PS3_Moderate, PP3, PM2_Supporting, PP3. (Classification approved by the ClinGen Lysosomal Diseases Variant Curation Expert Panel on June 6, 2024)