Familial Adenomatous Polyposis (APC) Sequencing

Background Information for Familial Adenomatous Polyposis (APC) Sequencing:
Characteristics of APC-associated Polyposis:
Familial Adenomatous Polyposis (FAP): Development of hundreds to thousands of adenomatous colonic polyps beginning in early adolescence; lifetime risk for cancer is 100 percent. Additional findings may include dental anomalies, polyps of the gastric fundus and duodenum, and congenital hypertrophy of the retinal pigment epithelium (CHRPE).
Attenuated FAP: Fewer colonic adenomatous polyps (average of 30), which are more proximally located and cancer generally occurs at a later age; lifetime risk for cancer is 70 percent.
Gardner syndrome: Multiple colonic adenomatous polyps along with osteomas, desmoid tumors, and soft tissue tumors.
Incidence:  Less than 1 percent of colorectal cancer cases.
Inheritance:  Autosomal dominant.
Penetrance:  Greater than 99 percent in untreated individuals.
Causes:  Pathogenic APC allelic variations
Clinical Sensitivity: Approximately 90 percent for classic FAP and less than 30 percent for attenuated FAP.
Methodology: Bidirectional sequencing of the APC coding region and intron-exon boundaries. 
Analytical Sensitivity and Specificity: 99 percent.
Limitations: Diagnostic errors can occur due to rare sequence variations. Regulatory region mutations, deep intronic mutations, and large deletion/duplications will not be detected. This assay is not designed to detect somatic variants associated with malignancy. Interpretation of this test result may be impacted if the patient has had an allogeneic stem cell transplantation.