Submissions for variant NM_000038.6(APC):c.220G>T (p.Glu74Ter)

dbSNP: rs876658941

Total submissions: 5

Submitter	RCV	SCV	Clinical significance	Condition	Last evaluated	Review status	Method	Comment
Ambry Genetics	RCV000215333	SCV000274815	pathogenic	Hereditary cancer-predisposing syndrome	2021-05-30	criteria provided, single submitter	clinical testing	The c.220G>T pathogenic mutation (also known as p.E74*), located in coding exon 2 of the APC gene, results from a G to T substitution at nucleotide position 220. This changes the amino acid from a glutamic acid to a stop codon within coding exon 2. This mutation has been reported in one or more individuals with attenuated FAP (Ambry internal data; Stekrova Jet al. BMC Med Genet. 2007 Apr 5;8:16). This change occurs in the last base pair of coding exon 2, which makes it likely to have some effect on normal mRNA splicing and RNA studies have shown that this alteration results in a transcript with out-of-frame skipping of coding exon 2 (Ambry internal data; Schwarzová L et al. Fam. Cancer 2013 Mar; 12(1):35-42). This variant is considered to be rare based on population cohorts in the Genome Aggregation Database (gnomAD). This nucleotide position is highly conserved in available vertebrate species. In silico splice site analysis predicts that this alteration will weaken the native splice donor site and will result in the creation or strengthening of a novel splice donor site. Based on the supporting evidence, this alteration is interpreted as a disease-causing mutation. However, alterations that result in premature termination in coding exon 2 are associated with an attenuated phenotype and may have reduced penetrance compared to classic familial adenomatous polyposis syndrome. Clinical correlation is advised.
GeneDx	RCV000254875	SCV000322197	likely pathogenic	not provided	2016-11-08	criteria provided, single submitter	clinical testing	This variant is denoted APC c.220G>T at the cDNA level. Located in the last nucleotide of exon 3, it destroys a natural splice donor site and causes abnormal splicing. RNA analyses by Schwarzova et al. (2013) demonstrated that this variant results in skipping of exon 3, referred to as exon 2 using alternate nomenclature, as well as a second alternate transcript with skipping of exons 3 and 4 (also known as exons 2 and 3). These alternate transcripts may result in the production of some functional protein by using an alternate downstream AUG start codon at position 184. APC proteins produced from this alternate start codon have been shown to have normal cellular localization and ability to regulate B-catenin levels, which may explain the attenuated phenotype seen in some patients with 5' truncating APC variants (Heppner Goss 2002). APC c.220G>T has been seen in at least one individual with colorectal cancer who was reported to have attenuated familial adenomatous polyposis (AFAP), though the number of polyps was not described (Stekrova 2007). Although the nucleotide substitution is predicted to result in the change of a Glutamic Acid to a premature stop codon, and is called Glu74Ter in the literature, we are only using the nucleotide nomenclature to refer to the variant since it is not clear if any truncated protein from the premature stop codon is translated or if the observed abnormal splicing mitigates the effect of the premature stop codon. APC c.220G>T was not observed in approximately 6,500 individuals of European and African American ancestry in the NHLBI Exome Sequencing Project, suggesting it is not a common benign variant in these populations. Based on currently available evidence, we consider APC c.220G>T to be a likely pathogenic variant.
Invitae	RCV002228955	SCV000552521	pathogenic	Familial adenomatous polyposis 1	2023-09-25	criteria provided, single submitter	clinical testing	ClinVar contains an entry for this variant (Variation ID: 231074). Studies have shown that this premature translational stop signal results in skipping of exon 3 and introduces a premature termination codon (Invitae). The resulting mRNA is expected to undergo nonsense-mediated decay. For these reasons, this variant has been classified as Pathogenic. This premature translational stop signal has been observed in individual(s) with attenuated adenomatous polyposis (PMID: 17411426). This variant is not present in population databases (gnomAD no frequency). This sequence change creates a premature translational stop signal (p.Glu74*) in the APC gene. RNA analysis indicates that this premature translational stop signal induces altered splicing and may result in an absent or disrupted protein product.
Myriad Genetics, Inc.	RCV002228955	SCV004044525	pathogenic	Familial adenomatous polyposis 1	2023-04-25	criteria provided, single submitter	clinical testing	This variant is considered pathogenic. This variant creates a termination codon and is predicted to result in premature protein truncation.
Department of Pathology and Laboratory Medicine, Sinai Health System	RCV000501460	SCV000591020	pathogenic	Carcinoma of colon		no assertion criteria provided	clinical testing	The APC p.Glu74X variant was identified in a family with an attenuated form of familial adenomatous polyposis (Schwarzova 2012). The p.Glu74X variant was also identified in HGMD, “InSiGHT Colon Cancer Database” and LOVD. This alteration would typically be predicted to result in a truncated or absent protein and loss of function; however, one study has demonstrated that for APC mutations closer to the 5’ terminus, an internal ribosome entry site is utilized to initiate translation at codon 184, resulting in a partially functional N-terminally truncated protein, which results in an attenuated phenotype (Heppner Goss 2002). The p.Glu74X variant occurs in the last base of the exon. This position has been shown to be part of the splicing consensus sequence and variants involving this position sometimes affect splicing. In a functional study by Schwarzova (2012), mRNA analysis showed that this variant created an aberrant splicing product which skipped exon 2 and could lead to expression of a truncated protein 48 amino acids long, or that would partly be subject to nonsense mediated decay. However, the authors of this study found another alternatively spliced APC transcript in all mRNA samples from control colon mucosa; this transcript was also found in the proband’s mRNA isolated from blood, but not in control blood samples. The authors suggest that the presence of this transcript in the patient’s blood may lead to the attenuated phenotype shown in the positive proband’s family. In summary, based on the above information, this variant meets our laboratory’s criteria to be classified as pathogenic.