The NM_000152.5:c.1211A>G variant in GAA is a missense variant predicted to cause substitution of aspartic acid by glycine at amino acid 404 (p.Asp404Gly). It has been reported in two individuals from the same family with Pompe disease: an adult with documentation of deficient GAA and clinical features consistent with LOPD, and a child with documentation of deficient GAA and clinical features of IOPD; both individuals treated enzyme replacement therapy (PMID: 24384324) (PP4_moderate). Both individuals are compound heterozygous for the variant, the adult individual had the variant in trans with c.695+5G>T (phase confirmed) and the child had the variant in trans (phase confirmed) with a variant that has been classified as pathogenic by the ClinGen Lysosomal Diseases VCEP, c.1798C>T (PM3). The highest population minor allele frequency in gnomAD v4.1.0 is 0.000001695 (2/1179940 alleles) in the European (non-Finnish)] population, which is lower than the ClinGen Lysosomal Diseases VCEP’s threshold for PM2_Supporting (<0.001), meeting this criterion (PM2_Supporting). This variant alters amino acid Asp404, a residue that crystallography studies have shown to be important in the active site of GAA, and therefore has been defined as a critical residue by the ClinGen Lysosomal Diseases VCEP (https://www.biorxiv.org/content/10.1101/212837v1.full.pdf, PMID: 29061980) (PM1). When expressed in HEK293T cells, this variant resulted in normal intracellular amounts of 110 kDa precursor, 95 kDa intermediate, and 76 kDa mature forms of GAA but 12.6% wild type GAA activity in cells and 4.6% in culture media. This suggests that this variant results in a catalytic deficiency but does not impact GAA synthesis and processing. The computational predictor REVEL gives a score of 0.968 which is above the threshold of 0.7, evidence that correlates with impact to GAA function (PP3). There is a ClinVar entry for this variant (Variation ID: 959950 , 2-star review status) with 2 submitters classifying the variant as pathogenic. In summary, this variant meets the criteria to be classified as likely pathogenic for Pompe disease based on the ACMG/AMP criteria applied, as specified by the ClinGen Lysosomal Diseases Variant Curation Expert panel (specifications Version 2.0): PP4_moderate, PM3, PM2_supporting, PM1, PS3_supporting (Classification approved by the ClinGen Lysosomal Diseases Variant Curation Expert Panel on April 15, 2025)