The NM_000152.5: c.1655T>C variant in GAA is a missense variant predicted to cause substitution of leucine by proline at amino acid 552 (p.Leu552Pro). More than 10 individuals diagnosed with Pompe disease have been reported with this variant including at least 7 probands for whom laboratory data is published showing GAA activity in the deficient range (PMID 12923862, 18285536, 25681614, 27666774)(PP4_Moderate). Eight of these individuals were compound heterozygous for the variant and a pathogenic variant, phase unknown in all cases (PMID 12923862, 18285536, 18607768, 20033296, 25681614, 29122469 29422078, and two individuals were homozygotes (PMID 27666774)(PM3_Very strong). The highest population minor allele frequency in gnomAD v2.1.1 is 0.00007 (European non-Finnish) which is lower than the ClinGen LSD VCEP threshold (<0.001) for PM2_Supporting. In two functional studies, this variant has been shown to result in significantly decreased GAA activity (<5%) and abnormal processing when expressed in COS cells (PMIDs 14695532, 19862843)(PS3_Moderate). The computational predictor REVEL gives a score of 0.94, 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: 279811, 2 star review status) with nine submitters all classifying the variant as pathogenic. In summary, the variant meets the criteria to be classified as pathogenic for Pompe disease. ACMG/AMP criteria met, as specified by the ClinGen LSD VCEP (Specifications Version 2.0): PM3_Very Strong, PS3_Moderate, PP4_Moderate, PM2_Supporting, PP3. (Classification approved August 17, 2021)