The NM_000203.5:c.1728-1G>C variant in IDUA occurs within the canonical splice acceptor site of intron 12. It is predicted to cause skipping of biologically-relevant exon 13 out of 14, resulting in a frameshift leading to nonsense mediated decay in a gene in which loss-of-function is an established disease mechanism (PVS1). At least 3 patients with this variant had documented IDUA deficiency within the affected range and urinary GAG elevation above normal range (PP4; PMID: 31194252). This variant has been detected in at least 2 individuals with MPS I. Of those individuals, both were compound heterozygous for the variant and a pathogenic variant (Q70X; W402X) and neither of those were confirmed in trans (PM3; PMID: 31194252). The highest population minor allele frequency in gnomAD v4.0. is 0.00001612 (19/1178792 alleles) in the European (non-Finnish) population, which is lower than the ClinGen Lysosomal Diseases VCEP’s threshold for PM2_Supporting (<0.00025), meeting this criterion (PM2_Supporting). In summary, this variant meets the criteria to be classified as pathogenic for MPS I based on the IDUA-specific ACMG/AMP criteria applied, as specified by the ClinGen Lysosomal Diseases Variant Curation Expert panel (Specifications Version 1.0): PVS1, PP4, PM3, PM2_Supporting. (Classification approved by the ClinGen Lysosomal Diseases Variant Curation Expert Panel on December 5, 2024)