Definition

Germline pathogenic variants in the APC gene lead to uncontrolled activation of the Wnt signaling pathway, causing hundreds to thousands of adenomatous polyps to form in the colorectal mucosa (classic FAP) or a smaller number of polyps (attenuated FAP); if left untreated, progression to colorectal cancer is almost inevitable (usually before age 40). Extracolonic findings (osteomas, epidermoid cysts, CHRPE, desmoid tumors) are part of the FAP spectrum.

Gene/region examined

APC - Exon 2, APC - Exon 3, APC - Exon 4, APC - Exon 5, APC - Exon 6, APC - Exon 7, APC - Exon 8, APC - Exon 9, APC - Exon 10, APC - Exon 11, APC - Exon 12, APC - Exon 13, APC - Exon 14, APC - Exon 15, APC - Exon 16

Method

Sequence analysis

Accepted sample types

EDTA blood, AF, CVS

Inheritance

Hereditary, autosomal dominant (AD); a somatic second-hit mutation is additionally required for colon tumors to form (two-hit hypothesis).

Related Tests

Inheritance Patterns

Describes how a genetic condition is passed on within a family. There are five main patterns

Go to term →

Carrier (Heterozygous / Homozygous)

Why it matters: In autosomal recessive inheritance, when each parent is a carrier (while both appear healthy), the chance of their child being born with the disease is 25% in each

Go to term →

VUS (Variant of Uncertain Significance)

This is the situation where the test has detected a change in the DNA, but the role of this change in the development of disease is unconfirmed.

Go to term →

How to Read a Genetic Test Result (Positive / Negative / VUS)

A genetic test result falls into three main categories

Go to term →

Types of Genetic Tests

A genetic test is a type of medical test that detects changes in genes, chromosomes or proteins. Today there are more than 77,000 genetic tests available.

Go to term →