Understanding the gut
The gut starts at the mouth and ends at the anus. When we eat or drink, the food and liquid travel down the gullet (oesophagus) into the stomach. The stomach churns up the food and then passes it into the small intestine.
The small intestine (sometimes called the small bowel) is several metres long and is where food is digested and absorbed. Undigested food, water and waste products are then passed into the large intestine (sometimes called the large bowel).
The colon and back passage (rectum) are parts of the gut (gastrointestinal tract).
The main part of the large intestine is called the colon, which is about 150 cm long. This is split into four sections, the ascending, transverse, descending and sigmoid colon. Some water and salts are absorbed into the body from the colon. The colon leads into the rectum, which is about 15 cm long. The rectum stores stools (faeces) before they are passed out from the anus.
Familial adenomatous polyposis (FAP), familial polyposis coli
Familial polyposis of the colon causes widespread development of adenomas in the colon and rectum. The number of polyps can range from no detectable polyps at colonoscopy to more than 7,000 seen on resected specimens of bowel. The polyposis predominantly affects the distal colon
Attenuated familial adenomatous polyposis
Attenuated familial adenomatous polyposis (AFAP) is characterised by fewer colonic polyps (100 or less) and a delayed onset of symptoms and complications. The colonic polyps tend to involve the proximal colon and spare the rectum.
There is a delay in onset of adenomatosis and bowel symptoms of 20-25 years, a delay in onset of colorectal cancer of 10-20 years and a delay in death from colorectal cancer of 15-20 years. Because of the tendency to affect the proximal colon, colonoscopy is preferred to sigmoidoscopy for surveillance, which should begin at the age of 20-25 years.
There are often associated gastric and duodenal adenomas, and so regular upper gastrointestinal endoscopy is also recommended.
Gardner’s syndrome is characterised by colonic polyposis with osteomas and soft tissue tumours.
Turcot’s syndrome is the association of colonic polyposis and tumours of the central nervous system.
The incidence of familial polyposis of the colon is about 1 in 10,000 live births. Colonic polyps begin developing at a mean age of 15 years.
Familial polyposis syndromes have autosomal dominant inheritance with almost complete penetrance but marked variation in expression. Mutations of the APC gene on chromosome 5 are thought to be responsible. The location of the mutation on the gene is thought to influence the nature of the extra-colonic manifestations.
Other commonly associated features
Congenital hypertrophy of the retinal pigment epithelium (CHRPE)
– evaluated by slit-lamp examination and indirect ophthalmoscopy – which can be a useful early clue as to whether the patient is a carrier of the APC gene.
Dental problems – supernumerary teeth, odontomas, non-erupted teeth
Desmoid tumours or osteomas (skull, endosteal and exosteal osteomas)
Carcinoembryonic antigen testing: raised levels may indicate colorectal carcinoma.
LFTs to evaluate possible metastasis.
Faecal occult blood.
CT or MRI scan of the abdomen and pelvis.
Dental X-rays, CXR and skull X-ray (for jaw lesions, osteomas, supernumerary teeth).
Colonoscopy with biopsies: investigation of choice for diagnosis.
Upper gastrointestinal endoscopy: for evaluation of gastric and duodenal polyps.
Genetic testing: for the APC gene and its mutation. Prenatal testing is possible if a disease-causing mutation is identified in an affected family member.
Other hereditary polyposis syndromes include:
Adenomatous polyposis syndromes – eg, Turcot’s syndrome
Hamartomatous polyposis syndromes – eg, Peutz-Jeghers’ syndrome, juvenile polyposis and Cowden’s disease
Peutz-Jeghers syndrome is an autosomal dominant disorder (with high penetrance) characterised by mucosal pigmentation of the lips and gums with multiple intestinal hamartomatous polyps
There is an associated marked increased risk of certain malignancies, especially gastro-oesophageal, small bowel, colorectal and pancreatic.
There is also risk of ductal breast cancer, thyroid, lung, uterine, Sertoli cell testicular tumours or ovarian sex cord tumours.
The estimate of the prevalence of Peutz-Jeghers syndrome is about 1 in 50,000
In up to two thirds of cases, mutations can be identified in the serine/threonine kinase gene STK11(LKB1) on chromosome 19 (19p13.3).
Family history: asymptomatic but requesting investigation/counseling.
Deeply pigmented lesions on the lips (cross the vermillion border) and buccal mucosa. These may also be present on the hands and feet (particularly the palms and the soles) and around the anus and genitalia.
These lesions may be most prominent in infancy and fade after puberty.
Repeated bouts of abdominal pain in a young patient (due to obstruction or intussusception).
Unexplained intestinal bleeding in a young patient or iron-deficiency anemia.
May also present with rectal prolapse, precocious puberty, or with nasal, bronchial, biliary tract, uterine or bladder polyps.
If Peutz-Jeghers syndrome is suspected the patient should be referred to a genetics centre for mutation analysis of the relevant gene. Surgical excision of lesions may be required:
Endoscopic polypectomy for diagnosis and control of symptoms.
Polypectomy using double balloon enteroscopy may prevent the need for repeated urgent operations and small bowel resection that leads to short bowel syndrome
Colorectal surveillance: large bowel surveillance is recommended two-yearly from the age of 25 years. The intervention should visualise the whole colon and so colonoscopy is the preferred mode of surveillance.
Members of the family of an affected family where a causative gene has been identified should be referred for gene counselling and predictive gene testing. Where they test negative, there is no indication for their continued surveillance.
Diseases associated with familial polyposis coli
The majority of patients have one or more extra-colonic features Extra-colonic features include:
Screening by flexible sigmoidoscopy with biopsy of polyps for histological diagnosis confirms the condition and allows surgery before the age of 20.
Aspirin and celecoxib may reduce recurrence of adenomas and the incidence of advanced adenomas in individuals with an increased risk of colorectal cancer
Sulindac, tamoxifen, or a combination of both, have been used for people with familial polyposis and desmoid tumours
The types of surgery are:
Proctocolectomy with ileostomy.
Total colectomy with ileo-rectal anastomosis.
Restorative proctocolectomy with ileo pouch anal anastomosis – the main surgical treatment for patients with FAP
Complications secondary to polyps lining the colon include:
Malignant change (if prophylactic colectomy is not performed). The risk of colorectal cancer increases with the number of polyps:
The mean age of colon cancer diagnosis in untreated individuals is 35-40 years).
Patients with more than 1,000 polyps have been proven to have 2.3 times the cancer risk compared to patients with fewer than 1,000 polyps.
Colon cancer will develop in all affected individuals unless prophylactic colectomy is performed. After total colectomy with ileo-rectal anastomosis, the recurrence rate is 30% after 20 years and 45% after 30 years.
Screening family members by flexible sigmoidoscopy confirms or eliminates the diagnosis.