Second-tier diagnostic or predictive test for familial adenomatous polyposis. Order if no variants were detected by APC sequencing, or concurrently with Familial Adenomatous Polyposis (APC) Sequencing (2004863), or if there is a known familial APC deletion.
- Patient Preparation
- Lavender (EDTA), pink (K2EDTA), or yellow (ACD Solution A or B).
- Specimen Preparation
- Transport 3 mL whole blood. (Min: 1 mL)
- Storage/Transport Temperature
- Unacceptable Conditions
- Ambient: 72 hours; Refrigerated: 1 week; Frozen: Unacceptable
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 with classic FAP.
Cause: Pathogenic APC mutations.
Clinical Sensitivity: Approximately 8-12 percent for classic FAP.
Methodology: Multiplex ligation-dependent probe amplification (MLPA) to detect large APC coding region deletions and duplications.
Analytical Sensitivity and Specificity of MLPA: 99percent.
Limitations: Diagnostic errors can occur due to rare sequence variations. Single base pair substitutions, small deletions/duplications, regulatory region mutations, and deep intronic mutations will not be detected. Deletion/duplication breakpoints will not be determined. Mutations in genes other than APC will not be detected.
Counseling and informed consent are recommended for genetic testing. Consent forms are available online.
|Component Test Code*||Component Chart Name||LOINC|
|2004921||FAP (APC) Del/Dup Specimen||31208-2|
|2004922||FAP (APC) Del/Dup Interpretation||20990-8|
- APC-Associated Polyposis
- Attenuated FAP
- Gardner Syndrome
- Turcot Syndrome