The NM_000152.5:c.1912G>T variant in GAA is predicted to result in the substitution of glycine by tryptophan at amino acid 638, (p.Gly638Trp). At least 14 individuals diagnosed with Pompe disease have been reported with this variant. Of those individuals, two have symptoms reported to be consistent with infantile onset Pompe disease (including cardiac symptoms and hypotonia) and are on enzyme replacement therapy (PMIDs:19588081, 28763149, 31086307), and two patients with late onset Pompe disease are reported with laboratory values showing reduced GAA activity (PMIDs: 36299500) and two of them are also treated with ERT (PMIDs: 24923245, 17573812, 17643989, 21484825, 25455803, 27189384) (PP4_Moderate). Ten individuals are compound heterozygous for the variant and another variant in GAA that has been classified as pathogenic or likely pathogenic by the ClinGen LD VCEP. The second variant includes c.-32-13T>G (ClinVar Variation ID: 4027) (7 individuals, all phase unknown; max 1 point counted) (PMIDs: 10737124, 24923245, 28763149, 29181627, 30564623, 36299500); c.2481+102_2646+31del, phase unknown, 0.5 points (PMID: 29122469), and c.2608C>T (p.Arg870Ter) (ClinVar Variation ID: 189009, SCV001371741.1) (confirmed in trans, 1 point) (PMID: 28763149, 31086307) (ClinVar Variation ID: 189009, SCV001371741.1), and c.1913G>T (p.Gly638Val) (confirmed in trans, 1 point) (PMID: 19588081). At least one individual is homozygous for the variant (PMIDs: 18429042, 31086307). Total 4 points (PM3_VeryStrong). In addition, three individuals are compound heterozygous for the variant and either c.1829C>T (p.Ala610Val) (PMID: 17573812, 17643989, 21484825, 25455803, 27189384), c.2294G>A (p.Gly765Asp) (PMID: 24627108), c.2294G>A (p.Gly765Asp) (PMID: 31086307). The allelic data for these individuals will be used in the assessment of the second variant and was not included here to avoid circular logic. The highest population minor allele frequency (MAF) in gnomAD v2.1.1. is 0.00006752 (1/14810 alleles) in the African/African-American population, which is lower than the ClinGen Lysosomal Diseases VCEP’s threshold for PM2_Supporting (<0.001), meeting this criterion (PM2_Supporting). In gnomAD v4.1. the highest MAF is 0.00001335 (1/74902 alleles) in the African/African-American population, also meeting PM2_Supporting. When expressed in COS-7 cells, the variant resulted in <2% control activity (PMID: 19862843). The computational predictor REVEL gives a score of 0.988 which is above the threshold of 0.7, evidence that correlates with impact to GAA function (PP3). Another amino acid change at the same position, c.1913G>T (p.Gly638Val), has been reported in patients with Pompe disease. This data was used in the assessment of p.Gly638Val and is not included here to avoid circular logic.. There is a ClinVar entry for this variant (ClinVar Variation ID: 280954) In summary, this variant meets the criteria to be classified as pathogenic for Pompe disease. GAA-specific ACMG/AMP criteria applied, as specified by the ClinGen Lysosomal Diseases VCEP (Specifications Version 2.0): PM3_VeryStrong, PP4_Moderate, PP3, PS3_Supporting, PM2_Supporting. (Classification approved by the ClinGen Lysosomal Diseases Variant Curation Expert Panel on June 6, 2024)