APC p.Arg99Trp

The c.295C>T variant in APC is a missense variant predicted to cause substitution of Arginine by Tryptophan at amino acid position 99 (p.Arg99Trp). APC is defined by the ClinGen InSiGHT Hereditary Colorectal Cancer/Polyposis Variant Curation Expert Panel (HCCP VCEP) as a gene for which primarily truncating variants are known to cause disease (BP1). The highest population minor allele frequency of the variant c.295C>T in gnomAD v2.1.1 (non-cancer) is 0.0007355 (95/129170 alleles) in the European (non-Finnish) population, which is higher than the HCCP VCEP threshold (≥ 0.001%) for BS1 (BS1). This variant has been observed in heterozygous state in more than 1000 healthy unrelated adult individuals worth ≥ 10 healthy individual points in total (BS2; Invitae and Ambry Genetics internal data). It has also been observed once in a homozygous state (Ambry Genetics internal data). This variant has been observed 4 times with other APC variants deemed (likely) pathogenic by the HCCP VCEP in individuals with FAP (BP2; PMIDs 23159591, 25604157, Bonn internal data). Finally, this variant has been observed in 6 patients with an alternate molecular basis for disease (BP5; Leiden University Medical Center internal data). In summary, this variant meets the criteria to be classified as Benign for FAP based on the ACMG/AMP criteria applied, as specified by the HCCP VCEP: BS1, BS2, BP1, BP2 (VCEP specifications version 1; date of approval 12/12/2022).