The c.1311_1312+1del variant in APC occurs within the canonical splice donor site of intron 10. It is predicted to cause skipping of exon 10, resulting in a frameshift in a gene in which loss-of-function is an established disease mechanism (PVS1). This variant has been reported in a family with FAP and CHRPE (father [index] and two affected children), resulting in a total phenotype score of 1 (PS4_supporting). The variant occurred de novo in the index patient (paternity/ maternity confirmed; PS2). The variant is not reported in gnomAD (PM2_supporting). In summary, this variant meets the criteria to be classified as Pathogenic for FAP based on the ACMG/AMP criteria applied, as specified by the ClinGen InSiGHT Hereditary Colorectal Cancer/Polyposis Variant Curation Expert Panel: PVS1, PS2, PS4_supporting and PM2_supporting (VCEP specifications version 1; date of approval: 10/12/22).