The NM_000152.5: c.2815_2816del (p.Val939LeufsTer78) variant in GAA is a frameshift variant predicted to cause a premature stop codon in the last exon of the gene and therefore to escape nonsense mediated decay. The frameshift begins at amino acid 939; the normal GAA gene product is 952 amino acids in length. Hence <10% of the normal product is missing. The impact of adding an abnormal sequence of 78 amino acids to the C terminus of GAA, due to the frameshift, is unknown (PVS1_Moderate). At least 10 probands with this variant who have been diagnosed with Pompe disease have been described including 4 probands for whom residual GAA activity was provided and was either <1% normal in cultured skin fibroblasts (PMID 22538254) or below the normal range in dried blood spots (PMID: 37542277, https://doi.org/10.3390/metabo11070446). Two of these probands and at least 2 additional patients were on enzyme replacement therapy (PMID 22538254, 25316892, 32373469, https://www.neurology-asia.org/articles/neuroasia-2021-26(2)-413.pdf) (PP4_Moderate). Patients reported with this variant include compound heterozygotes for the variant and another pathogenic/likely pathogenic variant in GAA, phase unknown, including for c.118C>T (p.Arg40Ter) (ClinVar SCV001371737.1) (PMID 24269976, 0.5 points), c.1935C>A (p.Asp645Glu) (ClinVar SCV002032138.1) (PMIDs 22538254, 28394184, 32373469, at least two patients, 2 x 0.5 points), c.2238G>C (p.Trp746Cys) (ClinVar SCV002032122.1) (PMIDs: 25316892, 34647686, 0.5 points), c.1082C>T (p.Pro361Leu) (ClinVar SCV002540670.1) (PMID: 37542277, 0.5 points), and c.1843G>A (p.Gly615Arg) (ClinVar SCV002583372.1) (PMID: 37542277, 0.25 points) and c.2585delG (PMID 28394184, 0.25 points); and confirmed in trans with c.2238G>C (p.Trp746Cys) https://www.neurology-asia.org/articles/neuroasia-2021-26(2)-413.pdf, 1 point). Total 4 points for PM3 (PM3_VeryStrong). Another patient has been reported as compound heterozygous for the variant and c.266G>T (p.Arg89Leu) (https://doi.org/10.3390/metabo11070446). The in trans data from this patient will be used for the assessment of p.Arg89Leu and is not included here in order to avoid circular logic. For another patient described with Pompe disease and the variant, a second variant was not identified (PMID 10338092). The highest population minor allele frequency in gnomAD v2.1.1 is 0.0001631 (3/18388; no homozygotes), and in gnomAD v4.1.0. it is 0.00006684 (3/44884; no homozygotes) in the East Asian population, which is lower than the ClinGen LD VCEP's threshold (<0.001) for PM2_Supporting, meeting this criterion (PM2_Supporting). There is a ClinVar entry for this variant (Variation ID: 371481). In summary, this variant meets the criteria to be classified as pathogenic for Pompe disease. GAA-specific ACMG/AMP criteria met, as specified by the ClinGen Lysosomal Diseases Variant Curation Expert Panel (ACMG/AMP specifications version 2.0): PM3_VeryStrong, PVS1_Moderate, PP4_Moderate, PM2_Supporting (Classification approved by the ClinGen Lysosomal Diseases Variant Curation Expert Panel on November 22, 2024)