Familial adenomatous polyposis (FAP) is a rare genetic condition associated with the growth of dozens to hundreds of polyps (abnormal growths or tumors) in the gastrointestinal (GI) tract. In FAP, the polyps are called adenomas, which typically begin to form in late childhood or early adolescence. If the entire colon is not removed, almost everyone who is diagnosed with FAP inevitably develops colorectal cancer by the age of 40-50 years.
These adenomas are generally found in the large intestine. However, many patients also develop polyps in other areas of the GI tract, such as the stomach and small intestine. The risk of developing cancer in these areas is much less than in the large intestine.
FAP occurs in approximately 1 in 10,000 people and affects both males and females equally. The condition is responsible for less than 1 percent of cases of colorectal cancer.
What causes FAP
FAP is caused by a defective gene called adenomatous polyposis coli (APC) that can cause of group of polyposis conditions with similar features:
- Gardner syndrome: A form of familial adenomatous polyposis (FAP) that causes multiple colorectal polyps and different types of tumors — both cancerous and non-cancerous.
- Turcot syndrome: A condition often associated with FAP. Children with this syndrome have multiple adenomatous polyps, an increased risk of colorectal cancer and an increased risk of brain cancer.
- Attenuated FAP (AFAP): A milder kind of FAP characterized by fewer polyps and the development of colorectal cancer at a later age. Less than 10 percent of families with FAP have an attenuated form.
- MYH Gene: An autosomal recessive condition in which both parents have to be carriers. Each individual offspring has a 25 percent risk of inheriting the condition.
FAP is an autosomal dominant condition, meaning that it can be passed down through families. If a child inherits the gene from one parent, there is a 50 percent they will have FAP. In some instances, FAP is not inherited but rather the result of a gene change, known as a mutation.
What are the symptoms of FAP?
There may be no symptoms in the early development of FAP, so often times it goes undetected. Abnormal signs and symptoms that may develop in the course of the disease include:
If your child has FAP, they may have other abnormal growths or lesions in other areas of the body, such as the thyroid, eyes, bone, teeth, brain, liver and skin. These can be either benign (non-cancerous) or malignant (cancerous) lesions.
Types of these lesions are listed below in order from most common to least common.
Benign (non-cancerous) lesions
- small black dots in the back of the eye (congenital hypertrophy of the retinal pigmented epithelium or CHRPE)
- fluid sac on the surface of the skin (epidermoid cysts)
- abnormal bone growth (osteoma)
- extra teeth (supernumerary teeth)
- tumor in the abdominal wall (desmoid tumor)
- tumor in the adrenal gland (adrenal gland adenomas)
Malignant (cancerous) lesions
How we care for FAP
The Boston Children's Hospital Polyposis Program was created to provide the highest quality comprehensive care to children with FAP. Our program is unique among polyposis programs in the U.S for its pediatric-focus and deep resources — from gastroenterology to radiology to genetics to surgery. We have the full spectrum of care and the benefit of working in close collaboration with one of the top cancer centers in the country that treats adults with FAP — Dana-Farber Cancer Institute.
